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This study investigates the vertical distribution characteristics of ozone (O 3) in the Pearl River Delta (PRD) region during spring, utilising observational data from two tall towers in urban and suburban areas of the PRD, i.e. , the 600 m high Canton Tower and the 356 m high Shenzhen Meteorology Gradient Tower (SZMGT), between 2018 and 2020. The observations indicate that the peak times of O 3 concentrations differ under polluted and clean conditions, with polluted conditions showing 1–3 h later peaks compared with clean conditions. The diurnal variation in the O 3 concentration is more pronounced at the SZMGT than at the Canton Tower. The O 3 vertical gradients differ between the two towers, with the Canton Tower showing larger daytime gradients and the SZMGT showing larger nighttime gradients under polluted conditions. The vertical O 3 distribution patterns are categorised into three types: Polluted, Moderate, and Good levels. The O 3 concentration initially rises with altitude and then decreases under polluted conditions. Elevated O 3 is observed in the lower planetary boundary layer (PBL), approximately between 110 and 210 m in height, where the concentration is 1.1–1.4 times higher than the surface level. Both the Moderate and Good levels occur under clean conditions, in which the O 3 of the Canton Tower increases with altitude, whereas the O 3 of the SZMGT first increases and then decreases with altitude. The correlation between O 3 and the meteorological conditions (temperature, relative humidity, wind direction, and wind speed) decreases with increasing altitude. The cluster analysis of backward trajectories identifies three main transport paths affecting the O 3 levels: northeasterly continental, southerly oceanic, and easterly coastal paths. Combining the observations from O 3 lidar in Guangzhou and Shenzhen and two additional cities within the PRD region, Foshan and Zhongshan, the analysis of a typical pollution case indicates that different cities have different local chemical generation and regional transport contributions to O 3 pollution. A conceptual model reflecting the horizontal transport paths and vertical structures of O 3 pollution in the spring over the PRD is proposed, which enhances our understanding of the O 3 vertical distribution in different cities and contributes to the analysis of the O 3 pollution mechanism in the PRD agglomeration. [Display omitted] • Data from two tall towers over 350 m in the PRD are used to study the vertical ozone characteristics and influencing factors. • Ozone in the PRD can be divided into three types of vertical distribution patterns and three horizontal transport paths. • A conceptual model of the vertical structure and horizontal transport paths of spring ozone in the PRD was established. [ABSTRACT FROM AUTHOR]

Biogenic volatile organic compounds (BVOC) play a crucial role in ground-level ozone formation, yet emission quantification faces considerable uncertainties stemming from input data. Land cover data, which determines the distribution of growth forms, is an essential driving input of BVOC emissions. This study explores the uncertainty in BVOC emission estimates arising from using two land cover datasets, specifically the MODIS and ESA land cover data, and the implications for ozone mitigation strategies in the Yangtze River Delta (YRD) region. By employing the MEGAN model for the year 2021, we estimated that ESA land cover data, with a finer 10 m resolution, yields a total BVOC emission estimate of 2299 Gg, which is over 52.9% higher than the MODIS dataset with a resolution of 500 m, attributed to the higher tree coverage (33.9% in ESA vs. 17.6% in MODIS) identified in the ESA dataset. We then simulated the ozone concentrations by both emission estimates with the WRF-CMAQ model. The elevated BVOC emissions based on the ESA data improved the underestimation of simulated isoprene concentrations and consequently resulted in more than 30% higher domain-averaged MDA8 ozone concentration compared to the MODIS-derived BVOC emission. Regarding ozone mitigation strategy, simulation with the ESA-based BVOC emissions results in 0.3–1.2 μg/m3 less ozone reductions compared to that with the MODIS-based emissions when reducing anthropogenic VOC emissions, but 0.7–2.9 μg/m3 higher ozone reductions when controlling anthropogenic NO x emissions. These disparities are more pronounced at the city level, highlighting the importance of accurate BVOC emission estimates for effective ozone control strategies. [Display omitted] • BVOC emissions were estimated based on two land cover datasets with varying spatial resolutions for YRD. • BVOC emissions were 52.9% higher when using ESA data compared to MODIS data for 2021. • The impact of BVOC emissions on ozone formation and the effectiveness of ozone mitigation strategies were investigated. [ABSTRACT FROM AUTHOR]

During the Lunar New Year of 2020, the Chinese government implemented a strict nationwide lockdown to prevent the spread of the COVID-19, which may have led to changes in the distribution of pollutants. To enhance our understanding of the three-dimensional evolution of pollutants under special control scenarios, this study used vehicle lidar to obtain vertical profiles of aerosols and ozone (O 3) in Wuhan during the pandemic. Combined with ground observations and WRF-Chem model simulation results, we explored the evolution characteristics of pollutants. The results showed that the fine particulate matter (PM 2.5) concentration near the ground in Wuhan City was significantly reduced (40%) during the emission control period. The aerosol concentration decreased rapidly with an increase in height, and the maximum loading height was consistent with the atmospheric boundary layer height. Conversely, due to factors such as the reduction of the precursor nitrogen dioxide (NO 2) and rising temperatures, the near-ground O 3 concentration increased by 59%. Despite the significant reduction in emission sources, lidar observations still captured distinct aerosol transport layers on March 7 and March 10, 2020. These transport layers gradually descended, affecting the ground-level aerosol concentration. Additionally, one typical process of O 3 external transport was observed in the vertical direction. Our study provides a theoretical basis for a deeper understanding of the spatiotemporal distribution characteristics of pollutants during special control scenarios, aiding policymakers in formulating effective air pollution control strategies. • Pollutant 3D evolution first analyzed using mobile vehicle-lidar during Wuhan's emergency control period. • The aerosol concentration decreased, and the concentration decreased with increasing altitude. • Despite the reduction in emissions, the ozone concentration increased. • External transport of pollutants was observed during the control period. [ABSTRACT FROM AUTHOR]

Chlorine radicals (Cl) play a crucial role in atmospheric chemistry. The COVID-19 (coronavirus disease 2019) pandemic significantly increased the use of chlorine-containing disinfectants in China, leading to enhanced emissions of chlorine gas (Cl 2) and hypochlorous acid (HOCl). In this study, we use the Community Multiscale Air Quality (CMAQ) model with updated chlorine chemistry to evaluate the potential air quality impact of chlorine emissions from disinfectant usage during February 2020, a month with a large outbreak of COVID-19 in mainland China. Results indicate that during the pandemic, there was a sharp increase of reactive chlorine emissions, with Cl 2 and HOCl emissions reaching 773.9 t and 5913.1 t, making 3 times increase. The emissions of chlorine enhanced atmospheric oxidation capacity (AOC) through the oxidation of VOC by Cl and OH, with the average enhancement in Shanghai, Beijing and Wuhan areas reaching 4.6% ± 1.8%, 10.3% ± 6.6% and 7.4% ± 4.6%, respectively. Consequently, the use of chlorine-containing disinfectants may have contributed to observed increases in the monthly average of the maximum daily 8-h average ozone (MDA8 O 3) and fine particulate matter (PM 2.5) concentrations by up to 1.5 ppbv (5%) and 1.7 μg/m3 (1%), respectively. Especially, the maximum hourly increase values of O 3 and PM 2.5 concentrations were 4.8 ppbv and 11.4 μg/m³, 2.5 ppbv and 4.5 μg/m³ in Beijing and Wuhan, respectively. These results indicate that chlorine emissions from the widespread use of disinfectants have had a significant impact on air quality in certain regions (Beijing and Wuhan) and during specific periods (9:00∼12:00). • Chlorine emissions from disinfectants usage during the COVID-19 are estimated. • Impact of chlorine emissions from disinfectant usage on air quality during the COVID-19 are predicted. • The chlorine emissions resulting from disinfectants usage during the pandemic may have enhanced O 3 and PM 2.5. [ABSTRACT FROM AUTHOR]

This study advances insights on ozone (O 3) concentration temporal cycles in Arizona, exploring differences between weekdays and weekends to understand the impact of anthropogenic activities on O 3 fluctuations. By examining data from six areas across Arizona and with a more detailed look across the Phoenix metropolitan area, this study compares O 3 and NO 2 levels based on day of the week and time of day as well as during five distinct seasons between January 2015 and December 2021: fall (Sep–Nov), winter (Dec–Feb), spring (Mar–May), dry summer (June), and monsoon summer (Jul–Aug). Results highlight associations between O 3 levels and O 3 precursor levels, particularly for nitrogen oxides (NO x) and volatile organic compounds (VOCs). Results show that O 3 levels are contingent on diurnal, day-of-week, and seasonally-dependent factors. This dependence influences the phenomena called the "weekend effect", which is most clearly observed at urban sites across Arizona in fall and winter seasons, wherein O 3 concentrations exhibit higher levels during weekends compared to weekdays. This study reveals opposing features during Arizona's warmer months and especially the monsoon summer period in which O 3 regimes reverse from VOC-sensitive (in fall and winter) to transition and NO x -sensitive regimes. A specific case study for Phoenix during the first COVID-19 lockdown (spring 2020) accounting for planetary boundary layer height normalization of gas concentrations shows that although NO 2 was reduced in March–April compared to other years, O 3 was also reduced due to a regional O 3 response as most areas surrounding western U.S. were typically either transitioning to, or already under, a NO x -limited regime. These findings provide insights into understanding the intricate relationship among anthropogenic emissions, seasonal fluctuations, and pollutant emissions and transport that influence O 3 levels across Arizona, potentially providing guidance for future study designs focused on effective control strategies for the sensitive months with most exceedances (∼June–August). • Weekend effect characteristics most evident in winter and fall seasons. • Monsoon period shown to be distinct from other periods for O 3 characteristics. • Regional O 3 reductions are influential for O 3 levels during Mar–Apr of COVID lockdown period. [ABSTRACT FROM AUTHOR]

Ozone (O 3) is a secondary atmospheric pollutant that can adversely impact human health, with production rates dependent on chemical precursors such as nitrogen oxides (NOx), Volatile Organic Compounds (VOCs), as well as meteorological variables such as incoming solar radiation, temperature, and humidity. NO x concentrations in Salt Lake City, UT (SLC), have decreased significantly since 2000 (−60%). However, during this time minimal declines in O 3 were observed. To better understand the drivers behind O 3 trends in SLC, we leveraged air quality measurements from sites maintained by the Utah Division of Air Quality, along with mobile O 3 measurements collected on top of a light-rail train that traverses the Salt Lake Valley (SLV). Analyses were carried out from March 15th through April (spring) and June through August (summer) for 2019, 2020, and 2021 and focused on the afternoon when O 3 was typically at the highest concentrations (1–4 p.m. MST). Overall, there were large differences in O 3 between the spring and summer months, with the latter being higher by ∼10 ppb. However, there were relatively small differences in O 3 between weekday and weekend. For the spring, differences in afternoon O 3 concentrations were higher during weekends (<12%), while during the summer, the differences were smaller (1–2%) and higher during weekdays. While weekday vs weekend differences in NO x emissions are usually large (∼20%) due to changes in traffic activity, there were relatively minimal differences in O 3 between weekday and weekends. There were minimal differences at point locations such as downtown SLC, and along multiple points along the TRAX train line. The analyses carried out in this study suggests that cities such as SLC are primarily under the influence of VOC-limited chemical regimes, meaning that there is limited O 3 sensitivity to changes in NO x. These results suggest that reducing VOC emissions, would be the most effective approach for reducing O 3 pollution in cities like SLC. • Ozone (O 3) levels in Salt Lake City exhibit slight decline despite a significant (−60%) reduction in NO x concentrations since 2000. • Seasonal variations in O 3 concentrations show summer levels are 10 ppb higher than spring, with weekday vs. weekend differences <12%. • Analysis indicates that Salt Lake City is mainly VOC-limited, stressing the need to reduce VOC emissions alongside NOx reductions to mitigate O3 pollution. [ABSTRACT FROM AUTHOR]

In recent years, China has continued to face persistent high concentrations of atmospheric O 3. While various methods can analyze the non-linear relationship between precursor emissions and O₃ concentrations, challenges remain in accurately quantifying the contributions of specific emission sources to O₃ levels due to the complexity of atmospheric chemistry and varying meteorological conditions. At the same time, changes in the atmospheric circulation situation can also affect the distribution of sensitive source areas for O 3 pollution in a given area. Therefore, the study of O 3 ″source-concentration" relationship under different types of polluted weather is of great significance for the development of scientific and effective O 3 control programmes. This study firstly screened the O 3 pollution processes based on the observed O 3 concentration data in Beijing, and summarised the O 3 pollution processes in Beijing into four types using subjective typing methods：Ridge-Internal Type (Type 1), Westward Flow Type (Type 2), Weak Ridge with Northwest Flow Type (Type 3), and Southwest Flow ahead of Trough Type (Type 4). The GRAPES-CUACE adjoint model version 2.0 was then used to carry out adjoint sensitivity analyses of O 3 concentrations for each type of individual case, to quantitatively assess the contribution of local and neighbouring precursor emission sources to O 3 concentrations in Beijing, and to further explore O 3 control options for each type of individual case. Adjoint sensitivity analyses showed that the four types of O 3 generation were controlled by different precursor emission sources and that there were significant differences in the distribution of sensitive source areas. Among the different types of individual cases, there were slight differences in the contributions of precursor emission sources from Beijing, Tianjin, Hebei, Shanxi and Shandong to the Maximum Daily 8-Hour Average O 3 concentrations (MDA8 O 3) in Beijing. In general, Beijing and Hebei sources contributed the most to the maximum 8-h average concentration of O 3 in Beijing, with a cumulative contribution of 66.4–85.6%. The emission reduction results of the 4 types of cases showed that the MDA8 O 3 in Beijing can be made to reach the set standard (70 ppb) through several iterations, which reflected the high efficiency of the adjoint model in the design of emission reduction experiments. When the O 3 concentrations of the four types of individual cases in this study were reached, the reduction percentages of NO x , VOCs and CO were 49.2–83.0%, 40.6–65.3% and 34.7–67.6%, respectively, in each province and city. By identifying the key precursor emission sources and their contributions to ozone levels under different weather types, this study provides good guidance for policymakers and environmental managers to develop more effective ozone reduction strategies. Specifically, the ability to predict the impact of various emission reduction scenarios under different weather conditions can help in designing targeted interventions that are both efficient and cost-effective. • Ozone generation varies with weather types, leading to notable differences in sensitive source area distribution. • Beijing and Hebei sources accounted for 66.4%–85.6% of the maximum 8-h average daily O 3 concentrations in Beijing. • The emission reduction rates of NOx, VOCs, and CO in various areas are 49.2% to 83.0%, 40.6% to 65.3%, and 34.7% to 67.6%. [ABSTRACT FROM AUTHOR]

Cigarette smoke and ozone (O 3) are two main pollutants in indoor environments and their mutual reaction can generate substantial detrimental substances having synergistic influences on the environment and human health. The aging process of cigarette smoke in the atmosphere is mainly gone through ozonolysis reaction attracting increasing attention in recent years. Herein, the ozonolysis reaction of cigarette smoke with indoor O 3 concentrations has been investigated in a Teflon chamber. The gas- and particle-phases of cigarette smoke are divided and their individual ozonolysis process can generate ultrafine particles (UFPs) with high number concentrations. The chemical compositions of the gas- and particle-phases of cigarette smoke as well as their nascent UFPs are measured and their differences during the ozonolysis have been clearly observed with vacuum ultraviolet (VUV) photoionization mass spectrometry. In particular, several representative key species of cigarette smoke, i.e. , the gas-phase furan and 2,5-dimethylfuran and the particle-phase nicotine, as well as their ozonolysis products are definitely identified and play an important role in the nucleation formation of UFPs. Their ozonolysis reaction mechanisms are also discussed. In addition, this work demonstrates that the ozonolysis of the particle-phase of cigarette smoke contributes more UFPs than that of the gas-phase. [Display omitted] • Ozonolysis reactions of cigarette smoke with indoor O 3 concentrations investigated. • Gas- and particle-phases of smoke generate ultrafine particles (UFPs) via ozonolysis. • Ozonolysis of particle-phase of smoke generates more UFPs than that of gas-phase. • Key species of smoke and their ozonolysis products are identified in mass spectra. [ABSTRACT FROM AUTHOR]

In coastal areas where many highly developed metropolis and city agglomeration are located, high ozone (O 3) concentrations are one of the most severe environmental problems, which is gravely impacted by the sea-land breeze (SLB) circulation. The complex terrain, such as coastal mountain, complicates SLB circulation and its impact on coastal O 3 pollution. Previous studies have shown that coastal mountain intensifies SLB circulation in various regions worldwide, such as the southern California coastal region, the Mediterranean coastal region, and the Beijing-Tianjin-Hebei region. However, the specific impacts of the underlying mechanism on coastal O 3 levels, along with a quantified contribution analysis, remain insufficiently explored. Here we present that the coastal mountain terrain in the Western Taiwan Strait of South China induces a three-dimensional O 3 transport involving SLB circulation through integrating observational data from 2015 to 2022 and employing WRF-Chem modeling, specifically focusing on the thermally driven sea breeze during the day combined with the up-slope flow generated by the coastal mountain. This flow carries O 3 -rich air mass, which are caused by both photochemical reactions and cross-boundary transport originating from land and offshore sources. As the air moves inland and up the mountainside, it ultimately forming a layer of high-level O 3 aloft. O 3 trapped in the layer acts as a reservoir of elevated O 3 for the coastal plain and aggravates O 3 pollution on the following day via vertical mixing by over 40 μg m−3 h−1. Based on the sensitivity simulation, this work quantifies that the coastal mountain contributes 23.4 % of surface O 3 concentrations increase in the coastal urban area. This recirculated transport of O 3 has important implications for understanding meteorological drivers on atmospheric environment in complex terrain. • The mountain-plain/urban-sea terrain induces a recirculated ozone transport involving SLB circulation. • The recirculated transport mechanism aggravates O 3 pollution over the mountainous coastal region by increasing vertical mixing contribution. • The coastal mountain contributes 23.4 % of surface O 3 concentrations increase in the coastal urban area. [ABSTRACT FROM AUTHOR]

Large amounts of aerosol in the atmosphere can cause significant attenuation of photochemical radiation and have a substantial impact on ozone and other secondary pollutants involved in photochemical reactions. This study examines the impact of aerosol actinic radiative effect on ozone and secondary pollutants during typical haze processes in the Pearl River Delta (PRD) region. The investigation employed lidar data and Weather Research Forecast–Community Multiscale Air Quality (WRF-CMAQ) modeling system. The results revealed that the aerosol caused a significant decrease in ground-level photolysis rates of NO 2 and ozone by 22% and 29%, respectively, when haze pollution was severe. The actinic radiative effect of aerosol caused an average reduction of more than 10 ppb in ground level ozone concentration in the PRD, with the core area experiencing a maximum reduction of 30 ppb. Additionally, the core area witnessed a maximum reduction of 2 ppb in peroxyacetyl nitrate (PAN) and 2 μg/m3 in PM 2.5. Due to reduced photolysis rates, nitrogen oxides increased by more than 5 ppb on average, reaching up to 10 ppb, while volatile organic compounds (VOCs) increased by a maximum of 10 ppb in the core region. Temporally, the aerosol actinic radiative effect was most pronounced in the morning and less significant in the afternoon. • During severe haze periods, the aerosol reduced the photolysis rates of ground level NO 2 and O 3 by 22% and 29%, respectively. • Aerosol actinic radiative effect reduced O 3 and PM 2.5 concentration but increased NOx, VOCs and nitrate in the haze process. • Aerosol actinic radiative effect during haze partially offset the positive feedback formed by its direct radiative effect. [ABSTRACT FROM AUTHOR]

Extensive epidemiological literature has documented adverse effects of ambient air pollution on human health. However, in Italy, no multicenter longitudinal studies on chronic exposure to air pollution and mortality have been conducted. Within the BIGEPI project, we aimed to investigate the association between long-term exposure to air pollution and cause-specific mortality in large Italian population-based cohorts. Five administrative cohorts from Turin, Bologna, Rome, Taranto, and Brindisi (Italy) were included. Subjects aged 30+ were enrolled from the 2011 Census, followed-up until 2018 (2019 for Bologna), and linked with population and health registries. Annual mean concentrations of particulate matter ≤10 and 2.5 μm (PM 10 and PM 2.5), dioxide nitrogen (NO 2), and warm-season ozone (O 3w) were assigned to each participant's geocoded residential address at baseline. Long-term associations between pollutants and non-accidental, cardiovascular, and respiratory mortality were investigated through single- and two-pollutant Cox proportional hazard models. Effect modification by sex and age was tested. Cohort-specific estimates were pooled in a random-effects meta-analysis. 2,709,903 subjects (contributing over 18 million person-years) generated 266,821 non-accidental deaths. Each increment of 5 μg/m3 of PM 10, 1 μg/m3 of PM 2.5 and 10 μg/m3 of NO 2 was associated with an increased risk of non-accidental mortality, with pooled Hazard Ratios (HR) of 1.018 (95% CI: 1.005–1.030), 1.004 (95% CI: 1.001–1.007) and 1.010 (95% CI: 1.002–1.018), respectively. HRs for cardiovascular and respiratory mortality were higher, the latter with CIs including the null. The associations remained quite stable after adjustment for the other pollutants. O 3w was negatively associated with mortality but estimates were not statistically significant and reduced to unity upon adjustment for NO 2. No consistent statistically significant effect modifications by sex and age emerged. Updated evidence implicates a continued risk of mortality in Italy due to long-term air pollution exposure, despite declining levels of exposure during the last years. [Display omitted] • First Italian multicenter longitudinal metropolitan study on air pollution and mortality. • Standardized protocols and fine-scale air pollution exposures. • PM and NO 2 were associated with higher risks of cause-specific mortality outcomes. • Air pollutant adverse effects did not change when adjusted for co-pollutants. • Despite declining air pollution levels, mortality effects remain consistently high. [ABSTRACT FROM AUTHOR]

Ozone (O 3) concentrations in the South Coast Air Basin (SoCAB) surrounding Los Angeles remain at unhealthy levels despite multiple decades of control programs designed to reduce emissions of precursor Volatile Organic Compounds (VOCs). Here we report on comprehensive VOC measurements made at Redlands, which has the highest measured O 3 concentrations in SoCAB, as part of the Re-Evaluating the Chemistry of Air Pollutants in California (RECAP-CA) field campaign (July–October 2021). Positive matrix factorization (PMF) analysis was applied to identify nine VOC factors. A photochemical chamber model initialized by field measurements was configured with a tagging technique to quantify the VOC factor contributions to O 3 formation in Redlands. Biogenic VOCs (BVOCs) made the largest contribution (26.6%) to O 3 formation, followed by traffic VOCs (21.2%), volatile chemical products (VCPs) (19%), and plant decomposition (14.9%). High O 3 episodes were not driven by increased VOC emissions from any single source, but rather were associated with stagnation events that concentrated VOCs from all sources and high temperature days that enhanced O 3 formation efficiency. This implies that VOC controls optimized to reduce O 3 concentrations would look similar in both the NO x -limited and VOC-limited regimes that can occur at Redlands. These results suggest that control strategies that reduce VOC and NO x emissions from the on-road vehicle fleet, such as increasing electrification, may yield O 3 reductions on days in both the NO x -limited and VOC-limited chemical regimes at Redlands. • PMF analysis resolved nine VOC factors in Redlands during the RECAP-CA field campaign (July–October 2021). • Source tagging with a chamber model quantified VOC factor contributions to O 3 in Redlands. • BVOCs, Traffic VOCs, and VCPs were the top VOC sources contributing to O 3 formation in Redlands. • VOC source contributions to O 3 formation had similar relative rankings under all atmospheric conditions. [ABSTRACT FROM AUTHOR]

To reduce economic and health impacts from poor air quality (AQ) in the U.S., the National Air Quality Forecasting Capability (NAQFC) at the National Oceanic and Atmospheric Administration (NOAA) produces forecasts of surface-level ozone (O 3), fine particulate matter (PM 2.5), and other pollutants so that advance notice and warning can be issued to help individuals and communities limit their exposure. The NAQFC uses the U.S. Environmental Protection Agency (EPA) Community Multiscale Air Quality (CMAQ) model for operational forecasts. This study is a first step in proposing a potential upgrade to the current operational NAQFC bias-correction system, by examining potential candidates for a gridded analysis ("truth") dataset. In this paper, we compare the performance of the "analysis" time series over the period of August 2020–December 2021 at EPA AirNow stations for both PM 2.5 and O 3 from raw Copernicus Atmosphere Monitoring Service (CAMS) reanalyses, raw CAMS near real-time forecasts, raw near real-time CMAQ forecasts, bias-corrected CAMS forecasts, and bias-corrected CMAQ forecasts (CMAQ FC BC). This 17-month period spans two wildfire seasons, to assess model "analysis" performance in high-end AQ events. In addition to determining the best-performing gridded product, this process allows us to benchmark the performance of CMAQ forecasts against other global datasets (CAMS reanalysis and forecasts). For both PM 2.5 and O 3 , the bias correction algorithm employed here greatly improved upon the raw model time series, and CMAQ FC BC was the best-performing model "analysis" time series, having the lowest RMSE, smallest bias error, and largest critical success index at multiple thresholds. • First step of a proposed improvement to operational AQ forecasting in the U.S. • Determined best dataset of PM 2.5 and O 3 to be gridded "truth" for analog ensemble. • Compared 17 months of raw and bias-corrected model time series vs. AirNow obs. • Bias-corrected CMAQ performed better than bias-corrected CAMS or raw CMAQ or CAMS. • CAMS reanalysis performed extremely poorly for PM 2.5 in 2020/2021 wildfire seasons. [ABSTRACT FROM AUTHOR]

Ozone (O 3) is produced by photochemical reactions of NO X and VOCs in the troposphere under sunlight. The column densities of formaldehyde (HCHO) and nitrogen dioxide (NO 2), derived from satellite data, serve as indicators of VOCs and NO X emissions in the troposphere. Through analyzing the unique characteristics of the threshold range for the HCHO/NO 2 ratio (FNR), the mechanisms of O 3 formation across different regions over a prolonged period can be identified. In this study, we utilized the Empirical Orthogonal Function (EOF) technique to characterize O 3 patterns during the warm season (April to October) spanning 2013–2019. This period is divided into three stages: 2013–2014, 2015–2016, and 2017–2019. Using the third-order fitting model, we assessed the FNR values across different regions in China: BTH (Beijing-Tianjin-Hebei), YRD (Yangtze River Delta), GD (Guangdong), and CY (Chuan-Yu). The FNR value ranges for these regions are as follows: ([1.2,2.0], [1.3,2.1], [2.4,3.2], [1.4,2.2]) during 2013–2014, ([1.1,1.9], [1.2,2.0], [2.0,2.8], [1.2,2.0]) during 2015–2016, and ([1.0,1.8], [1.0,1.8], [1.7,2.5], [1.1,1.9]) during 2017–2019, respectively. Ultimately, our research indicates a shift in certain regions from a VOC-limited regime towards a transitional regime. This shift correlates with a significant decline in anthropogenic NO X emissions, attributed to the stringent emission control strategies extensively implemented between 2013 and 2019. The spatial expansion of the transitional regime aligns with increasing O 3 concentrations, simultaneously offering guidance for the development of effective emission reduction strategies. • Comprehensive analysis of ozone formation in China, focusing on major regions including and using advanced methodologies like the Empirical Orthogonal Function (EOF) and polynomial model. • Clear categorization of regions into VOC S -limited, NO X -limited, and transition zones, emphasizing pollution dynamics and control factors. • Growing transition and NO x -limited zones in Beijing-Tianjin-Hebei and Yangtze Delta highlight the urgent need for NO x and VOC reduction strategies. [ABSTRACT FROM AUTHOR]

The interaction between ozone and temperature on cardiovascular biomarkers has not been thoroughly examined. A panel study was conducted among 40 college students with four equal interval follow-ups in Hefei, Anhui Province, China between August and October 2021. Real-time concentrations of ozone were collected from a nearby monitoring device. Temperature variability parameters included diurnal temperature range (DTR), the standard-deviation of temperature (SDT), and temperature variability (TV). A set of cardiovascular biomarkers were measured, including markers of inflammation (Granulocyte-macrophage colony-stimulating factor, GM-CSF and serum amyloid A, SAA), coagulation (D-dimer and ADAMTS13), oxidative stress (Myeloperoxidase, MPO and Growth differentiation factor-15, GDF-15), endothelial function (vascular endothelial growth factor A, VEGFA), and stress hormone (5-hydroxytryptamine, 5-HT). Linear mixed-effect models were conducted to analyze the associations between ozone, temperature variability, and all blood markers. The results showed significant associations among ozone, DTR, SDT, TV, and blood markers, suggesting harmful effects on markers. For instance, a 10-μg/m3 increase in ozone at lag 2d was associated with higher levels of SAA by 19.65% (95%CI: 13.70, 25.60), VEGFA by 10.90% (95%CI: 4.57, 17.22), GDF-15 by 5.33% (95%CI: 0.59, 10.06), and GM-CSF by 2.52% (95%CI: 1.70, 3.34), but 13.09% lower D-dimer (95%CI: 6.99, 19.19). We also found statistically significant interaction between ozone and TV exposures for GM-CSF and SAA. This study shows that ambient ozone and personal TV exposures may independently have acute effects on markers of inflammation, oxidative stress, coagulation, endothelial function, and neuroendocrine stress response. Simultaneous exposure to these factors may also lead to interactive effects on inflammation markers. These findings offer valuable insights for developing comprehensive strategies in cardiovascular disease control and prevention. [Display omitted] • O 3 and temperature variability had a synergistic effect on blood markers. • The joint effect of O 3 and temperature variability varied in direction and magnitude across inflammation markers. • O 3 was associated with inflammation, oxidative stress and endothelial function markers. • Temperature variability perturbed blood markers that are involved in numerous different downstream outcomes. [ABSTRACT FROM AUTHOR]

In August 2023, a detailed investigation of formaldehyde (HCHO) chemical characteristics on ozone (O 3) polluted days and non-O 3 polluted days in Wuhan was undertaken. The mean value of HCHO on O 3 polluted days (3.02 ± 1.15 ppbv) was 122% higher than that on non-O 3 polluted days (1.35 ± 0.41 ppbv). Utilizing Positive Matrix Factorization (PMF) model revealed secondary formation as the dominant HCHO source (58.3% on non-O 3 polluted days and 66.2% on O 3 polluted days). On O 3 polluted days, the contribution of liquefied petroleum gas (LPG)/solvent usage and industrial emissions to HCHO were 13.7% and 8.2%, respectively, whereas on non-O 3 polluted days, LPG/solvent use and diesel exhaust contributed 15.4% and 14.7%, respectively. The top ten species, with the highest Relative Incremental Reactivity (RIR) to HCHO, were mainly alkenes and aromatics, which remained consistent on both O 3 and non-O 3 polluted days. It is noteworthy that the RIR of isobutane to HCHO is significant in this study. Further reapportionment of secondary HCHO by a photochemical box model indicated that LPG/solvent usage (33.2%) contributed the most to HCHO on O 3 polluted days, while diesel exhaust (31.9%) dominated on non-O 3 polluted days. This research enhances understanding of HCHO in Wuhan, providing a theoretical basis for targeted pollution reduction and supporting efforts to improve air quality and public health. [Display omitted] • The concentration of HCHO was 2.22 times higher on O 3 polluted days compared to non-O 3 polluted days. • Six sources of HCHO were identified by the PMF model. • Secondary formation contributed to 58.3% of HCHO on O 3 polluted days and 66.2% on non-O 3 polluted days. • Secondary sources of HCHO were reapportioned using PBM-MCM combined with PMF. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM 2.5) and surface ozone air pollution have severe health consequences. Since China implemented the nationwide Air Pollution Prevention and Control Action Plan (APPCAP) in 2013, annual average PM 2.5 concentrations have decreased while O 3 concentration have increased in Beijing. It is unclear, however, to the extent that short-term meteorological variability has influenced these trends. To separate the influence of meteorology from long-term emissions-induced changes, we quantify the portion of the long-term PM 2.5 and O 3 concentration signals associated with short-term meteorological variability. Building off recent literature highlighting the regional nature of pollutant variability, we incorporate both locally observed meteorology and average regional reanalysis. We isolated sub-seasonal variability using the Kolmogorov-Zurbenko filter. Next, we trained and compared the utility of three statistical models of varying complexity (a linear model, a general additive model with splines, and a random forest) in their ability to predict out-of-sample daily concentrations. The random forest model yields the best predictive capability in holdout tests and predicts changing meteorological contributions to PM 2.5 and ozone concurrent with changing concentrations across the study period. Results show an overall decrease in meteorology induced PM 2.5 concentration variability at daily scales since 2013, but variability from meteorology has increased relative to mean PM 2.5 concentrations. In contrast, O 3 shows the opposite trend, with increasing meteorology-induced variability (meteorology-induced variability normalized by mean observed O 3 has decreased). Our results show the importance of including regional meteorology in explaining local PM 2.5 and O 3 variability and quantify links between long-term policy implementation and short-term meteorological contributions to pollutant concentrations. • Meteorological detrending applied to evaluate the effectiveness of China's air pollution policies since 2011. • Regional and local meteorology are both key predictors for daily PM 2.5 and O 3 concentration variability. • Both daily PM 2.5 and O 3 exhibit lower meteorology-induced variability in years with lower concentrations. [ABSTRACT FROM AUTHOR]

The dairy industry in California emits large amounts of methane (CH 4) that contributes significantly to the state's overall Greenhouse Gas (GHG) budget. Reducing CH 4 emissions has become a key priority for dairy farms in support of California's GHG reduction goals. Anaerobic digesters designed to capture CH 4 from animal manure present a practical option for reducing CH 4 emissions, but a comprehensive evaluation of the local air quality impacts of this technology has not been previously undertaken. The simplest digester configurations decrease local emissions of volatile organic compounds (VOCs) but increase emissions of oxides of nitrogen (NOx), potentially changing local air quality. Here, we evaluate the air quality implications of widespread digester adoption in the year 2050 across the San Joaquin Valley (SJV) in central California, which is home to the highest concentration of dairy farms in the state. Changes to concentrations of air pollutants including ozone (O 3), airborne particulate matter with diameter smaller than 2.5 μm (PM 2.5), and various PM 2.5 chemical components are predicted using the UCD/CIT chemical transport model at 4 km resolution. Dairy digester adoption is evaluated within two regional energy scenarios, including a business as usual (BAU) scenario and an 80% greenhouse gas reduction (GHGAi) scenario, to consider potential changes to the chemical regime that governs formation of secondary air pollution. Concentrations are evaluated across 32 randomly selected weeks over a 10-year period from the year 2046–2055 to establish a long-term average impact in the presence of El Niño Southern Oscillation (ENSO) variability. Regional weather patterns are downscaled from Global Climate Model simulations under the RCP8.5 global scenario. The results indicate that baseline dairy emissions make minor contributions to air pollutant concentrations in 2050. Under a worst-case scenario for digester adoption, PM 2.5 concentrations would increase by 0.06 μg/m3 (current standard = 9 μg/m3), and maximum daily 8-h average (MDA8) O 3 would change by −1.0 ppb to +0.2 ppb depending on the surrounding regional energy scenario (current standard = 70 ppb). A health impact analysis shows that the widespread use of dairy digesters would result in fewer than 0.1 additional deaths per 100,000 people due to changing air pollution. For comparison, this level of mortality change is more than 100 times smaller than the risk posed by seasonal flu. Further, Environmental Justice analysis indicates that the implementation of digesters will not influence the exposure disparities among different racial groups in either the SJV or the surrounding San Francisco Bay & Sacramento area. These findings suggest that dairy digesters can be widely adopted in central California to reduce GHG emissions with minimal effect on regional air quality and public health. • Dairy digesters capture methane from farms to reduce GHG emissions. • Digesters configured to produce electricity increase local emissions of criteria pollutants. • Widespread digester adoption would have minor effects on local air quality. • Digesters do not harm public health or worsen air quality for disadvantaged communities. [ABSTRACT FROM AUTHOR]

Tropospheric ozone (O 3) is a criteria air pollutants posing risks to organisms, and is expected to enhance formation due to climate change. Satellite-based measurements provide a promising approach to estimate ground-level air pollution on large scale. However, most applications of satellite-based measurements have been used for fine particulate matter and nitrogen dioxide, while only a few have been used for O 3. In this study, we incorporated satellite-based measurements from the Ozone Monitoring Instrument (OMI) and MOderate-resolution Imaging Spectroradiometer (MODIS) with meteorological variables and land-use data to estimate daily maximum 8-h average O 3 at 1-km resolution in Taiwan during 2004–2020. The random forest model was used to impute the missing values of the satellite-based measurements. Additionally, the XGBoost model was leveraged to estimate daily O 3 concentrations. Model performance was evaluated by the ten-fold cross-validation (CV), temporal and spatial validation, and the results were reported as the coefficient of determination (R 2 ) and root mean square error (RMSE). Our results showed that the 10-fold CV, temporal validated, and spatial validated R 2 (RMSE) of the XGBoost model were 0.82 (7.71 ppb), 0.63 (11.09 ppb), and 0.68 (10.27 ppb), respectively. Our model performance was better in central and southern Taiwan. The top ten important predictors were date (relative importance = 12.15%), temperature (10.77%), meridional wind (10.71%), relative humidity (9.60%), zonal wind (8.14%), UV radiation (8.07%), total precipitation (6.35%), surface pressure (5.34%), surface O 3 volume mixing ratio (4.93%), and boundary layer height (4.69%). The spatial distribution of O 3 estimates showed that daily maximum 8-h average O 3 concentrations were higher in the suburban and mountainous areas near the central and southern Taiwan. This reveals that sensitive populations should still pay attention to the secondary pollutants even when outside the urban areas. The O 3 estimates can be further leveraged to evaluate the short-term and long-term effects of O 3 on human health. [Display omitted] • An estimation model for DM8O3 at 1-km resolution during 2004–2020 was developed. • OMI and MODIS products were integrated in the model. • A stronger correlation between DM8O3 and surface volume mixing ratio was observed. • Cross-validated R 2 and RMSE of the XGBoost were 0.82 and 7.71 ppb, respectively. • Estimated DM8O3 were higher in the suburban and mountainous areas in Taiwan. [ABSTRACT FROM AUTHOR]

Westerly warm advection from the Loess Plateau to the over layer of North China Plain (NCP) suppresses the mixed layer during the daytime in summer, having already be confirmed as an important formation mechanism of regional O 3 pollution all over NCP. However, when NCP was simultaneously affected by the westerly warm advection from the Loess Plateau and the typhoon periphery airflow from the Western Pacific tropical cyclone system, a rare pollution pattern of surface O 3 was detected, characterized by a very low ozone pool in Beijing (LOP-BJ) contrast to much higher O 3 in surrounding areas. To explore the causes and deep formation mechanism to this special pollution phenomenon, regional pollution characteristics of O 3 , characteristics of the atmospheric boundary layer (ABL) structure and vertical airflows affected by different weather systems were analyzed based on the analysis of observations and three dimensional simulations. It was found that the synthetic impacts of the topography and the typhoon peripheral flow promoted the stabilization of the ABL and introduced a nearly isolated air mass in terms of both thermodynamic and dynamic structures within ABL in Beijing region. In the stable and isolated ABL air masses, the significant lower ozone near the ground was primarily attributed to the strong loss by NO titration consumption from local excessive emissions and extremely weak transport contributions from surrounding areas. The conclusion was also confirmed by the integrated process rate (IPR) analysis results of contributions from chemistry tendency (CHEM) and total transport tendency (TRAN) to surface ozone. Our work insight the understanding of the formation mechanism of regional ozone pollution and improve the forecasting capabilities under comprehensive weather conditions over NCP. • A rare pollution pattern LOP-BJ was detected in North China Plain. • Topography and typhoon periphery promoted the stabilization and isolation of the ABL. • LOP-BJ was attributed to the strong local consumption and weak external contribution. [ABSTRACT FROM AUTHOR]

We examined the spatial and temporal variations of nighttime ozone (O 3) excess days (NOEDs) in the North China Plain (NCP) during 2015–2022 by using the observed O 3 concentrations from the China National Environmental Monitoring Center network. The NOEDs were defined as those with any 1-h average O 3 concentration at night (20:00 to 06:00 local time) exceeding 200 μg m−3. The observations showed that the annual frequencies of NOEDs averaged over the 57 cities in the NCP were 1.56, 1.72, 6.23, 6.53, 8.84, 5.93, 5.07, and 6.86 days in 2015, 2016, 2017, 2018, 2019, 2020, 2021, and 2022, respectively, with a linear increasing trend of 0.66 d y−1. Using the K-means clustering method, two typical regional NOEDs types in the NCP were identified. Type1 had the highest frequencies of NOEDs in the southwest of NCP, while Type2 had the highest frequencies in the central NCP region. These two types contributed to 53.5% and 46.5% of the regional NOEDs in NCP, respectively. Compared with the regional non-NOEDs (with nighttime O 3 did not exceed but daytime O 3 exceeded O 3 air quality standard), both Type1 and Type2 NOEDs generally had higher temperature, lower relative humidity, and higher planetary boundary height in both afternoon and night, favoring the production and accumulation of O 3 in the afternoon as well as the persistent high O 3 at night. Corresponding weather patterns were also identified. These results have important implications for emission control strategies during NOEDs. Emission control measures can be applied once the dominant circulation patterns have been predicted. [Display omitted] • We examined the nighttime ozone excess days (NOEDs) in NCP during 2015–2022. • The frequency of NOEDs in 91.23% of cities in NCP had an upward trend over 2015–2022. • Two types of regional NOEDs were identified, which had different weather types. [ABSTRACT FROM AUTHOR]

Peroxyacetyl nitrate (PAN) ranks among the troposphere's most prevalent organic peroxy radicals, and the photochemical production and loss pathways of PAN are mainly related to the generation and consumption of PA radicals. PA radicals can affect the atmospheric O 3 generation by competing or providing precursors and affecting the atmospheric radical cycling. Field measurements took place at two sites in Shenzhen: the suburban site of Yangmeikeng Station (YMK) from September to October 2018, and the urban site of University town of Shenzhen (DXC) from September to October 2019. The average PAN levels of YMK and DXC were 0.57 and 0.87 ppb, which were similar to PAN concentrations in other southeastern coastal regions and lower than those in inland and northern regions in China. The model simulations showed that except PAN thermal decomposition, acetaldehyde (40.7% and 24.9%), other OVOCs (40.0% and 59.2%) and radical cycling (19.3% and 16.0%) were the major production pathways peroxyacetyl (PA) radicals at YMK and DXC. During the sampling period, the production of PAN resulted in a decreasing of local O 3 generation at YMK (5.32 ± 3.2 ppb) and DXC (3.53 ± 12.21 ppb). The findings could make us more comprehensively understand the mechanism of atmospheric formation of PAN in urban and suburban sites in Shenzhen and its influence on the process of atmospheric photochemical reaction in Shenzhen. • PAN, O 3 , VOCs and NO x were measured online at a suburban site (YMK) and an urban site (DXC) of Shenzhen from September to October 2018 and from September to October 2019, respectively. • The local PAN formation and photochemistry was simulated by using a master chemical mechanism based a photochemical box model (PBM-MCM). • During the sampling period, the PAN production resulted in a decrease of local O 3 generation at YMK (5.32 ± 3.2 ppb) and DXC (3.53 ± 12.21 ppb). [ABSTRACT FROM AUTHOR]

Understanding the impact of stratospheric intrusion (SI) is crucial for elucidating atmospheric complexities and implications for ozone (O 3) control. However, current studies have not focused on the influence of SI on surface O 3 , thus limiting the effectiveness of control strategies. This study delves into an SI event that occurred from March 5 to 12, 2022, employing a comprehensive integration of the Weather Research and Forecasting model coupled with Chemistry and multi-reanalysis data. The lower tropospheric O 3 enhancement in Hong Kong has been noticed, despite the absence of SIs in the upper troposphere. This study employed a comprehensive methodology, integrating the use of a box model to estimate the stratosphere–troposphere exchange (STE) O 3 flux, integrated process rate (IPR) analysis to quantify the contributions from individual physical and chemical processes, and tracer methods to detect stratospheric O 3. During the deep SI episode, the STE flux peaked at −81.33 × 10−8 kg m−2·s−1, surpassing the monthly average by 15.2-fold. The IPR results indicate that vertical transport within the 0–16 km range contributes between 18.4 and 39.0 ppbv h−1 during the SI event, whereas horizontal advection shows a negative contribution. Stratospheric O 3 tagging revealed that SI contributes 15.5–31.3 ppb (29.6–50.2%, respectively, of surface O 3) when stratospheric O 3 mixes down. Five emission reduction paths were designed in response to the negative impacts of SI. The "anthropogenic VOC (AVOC) only" path was the most efficient; however, when SI contributed 31 ppb on March 9, the "NOx only" path required a 69% reduction, while the "AVOC only" path required an 85% reduction for efficiency. This research not only elucidates the complex interplay between SI and surface O 3 concentrations but also emphasizes the significance of refining existing emission reduction paths. [Display omitted] • A distinctive stratospheric intrusion (SI) event in Hong Kong was evidenced. • Tagging method revealed that SI contributes 15.5–31.3 ppb to surface O 3 enhancement. • It is crucial to offset the adverse effects of SI on emission reduction strategies. • The optimal emission reduction path needs to be adjusted as the impact of SIs changes. [ABSTRACT FROM AUTHOR]

PM 2.5 and O 3 are the primary air pollutants affecting air quality in the Yangtze River Economic Belt (YREB). We analyzed the spatiotemporal distribution characteristics of the association between PM 2.5 and O 3 using the Pearson correlation coefficient and geographically weighted regression methods, as well as the effects of meteorological and emissions factors. In the YREB, pollution days attributed to PM 2.5 have consistently decreased, while pollution days attributed to O 3 began decreasing in 2020 after a continuous increase. When PM 2.5 levels were below approximately 37 μg/m3, O 3 levels increased as PM 2.5 levels rose. However, as PM 2.5 levels continued to increase, O 3 levels began to decline, except in the Yunnan-Kweichow Plateau (YKP). The inflection point gradually decreased from 64 μg/m3 in 2015 to 31 μg/m3 in 2021. The positive PM 2.5 –O 3 association strengthened from 2015 to 2018, and it reached a relatively stable state after 2018. Further investigation revealed that the O 3 levels were significantly affected by the boundary layer height (BLH) in the Sichuan Basin (SCB). In the YKP, PM 2.5 levels were more strongly affected by wind speed and BLH in spring. Emissions were predominantly positively associated with PM 2.5 , exhibiting a positive association with O 3 in summer but a negative one in winter. Temperature and solar radiation were the key factors affecting the PM 2.5 –O 3 association. In addition, the emission reductions of primary PM 2.5 , NH 3 , and NO x enhanced the PM 2.5 –O 3 association. • The association between PM 2.5 and O 3 in the YREB has stabilized since 2018. • Temperature and solar radiation were the key factors affecting this association. • Reductions in PM 2.5 , NH 3 , and NO x enhanced the association between PM 2.5 and O 3. [ABSTRACT FROM AUTHOR]

This study focusses on the environmental consequences of aircraft NO x emissions and their role and impact on ozone formation in the upper troposphere and lower stratosphere (UTLS). We use a global chemistry transport/box model approach to quantify the impacts of NO x on UTLS ozone over time scales of hours and over distance scales appropriate to air traffic corridors and aircraft flight paths. An important feature of our study has been to provide a marked contrast to the coarse spatial resolution of the global model studies typically employed to assess the impacts of aviation NO x on UTLS ozone. Real operational aviation routing data are used to quantify the NO x impacts on ozone at 235 locations on 21 flight paths. The NO x impact on ozone in the intercontinental air traffic corridors is strongest in the great circle routes from North America and Europe into Asia and weakest in the trans-polar routes. The NO x impacts identified with the CTM/box model combination are significantly smaller compared with those identified in the current global models typically used to assess aviation NO x impacts. Further research is required to confirm our assessment of those flight paths that appear to show greatest NO x – O 3 impacts and those the least and extend our analyses into the tropics and southern hemisphere. • Aircraft NO x emissions promote build-up of greenhouse gases methane and ozone. • NO x impact on ozone in intercontinental air traffic corridors is weakest on trans-polar routes. • NO x impact on ozone is strongest on the great circle routes into Asia from Europe and North America. [ABSTRACT FROM AUTHOR]

Dry deposition is an important ozone sink in the planetary boundary layer (PBL), but how different PBL parameterization schemes affect the ozone dry deposition impacts has not been well quantified. Here we investigate the influences of PBL mixing parameterizations on surface ozone and dry deposition in eastern China using a regional air quality model (WRF-Chem) and further quantify the contributions of dry deposition to ozone tendencies both near the surface and in the PBL with integrated process rates (IPR) analysis. We analyze three PBL schemes coupled with their corresponding surface layer (SFL) schemes, including Yonsei University (YSU), Mellor–Yamada–Janjić (MYJ), and Asymmetric Convective Model v2 (ACM2). We find that using different PBL-SFL schemes in general produces similar monthly mean meteorological fields, leading to relatively small uncertainties, ranging from 6.5% to 18.5% in monthly mean surface ozone concentrations and 3.6% to 15.3% in total ozone dry deposition in eastern China. However, these uncertainties can frequently exceed 30% in summer at the daily scale. IPR analyses with YSU_MM5 show that ozone dry deposition accounts for 80–89% of surface ozone losses and 45–58% of PBL ozone losses. Model sensitivity simulations by suppressing ozone dry deposition would enhance surface ozone in eastern China by 24–30% (20.6–35.7 μg m−3) during the daytime and 61–82% (26.0–46.1 μg m−3) at night. Ozone dry deposition significantly promotes the downward vertical mixing of ozone to the surface layer, which contributes to smoothing the near-surface ozone gradients as caused by ozone dry deposition and titration, thus explaining the smaller contribution estimated by the sensitivity approach than IPR analyses. We further show that different meteorological conditions simulated by different PBL-SFL schemes affect daily ozone simulations not only through the chemistry process as previously recognized but also considerably by the dry deposition process. [Display omitted] • The influences of PBL schemes on surface ozone and dry deposition in eastern China are investigated. • Different PBL schemes cause uncertainties of 3.6–15.3% in WRF-Chem simulated ozone dry deposition. • IPR analyses with YSU_MM5 show that ozone dry deposition accounts for 80–89% (45–58%) of surface (PBL) ozone losses. • Process analyses show dry deposition significantly promotes downward vertical mixing compensating for the surface ozone loss. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to evaluate the effectiveness of the measures for controlling ozone (O 3) pollution in Jinshan District, Shanghai, China during the summer months of June 2022–August 2022. The study period was divided into a control period (CP) when measures were enforced and a non-control period (NCP) without interventions. The concentrations of volatile organic compounds (VOCs) were compared between the two periods, with the ranking of various types of identical VOCs, in which alkanes exhibited the highest (39.48%) concentrations, followed by aromatics (24.35%), halohydrocarbons (19.94%) and alkenes (16.23%). Compared to NCP, the mean levels of VOCs were 32.67% lower in CP, indicating the control measures significantly reduced the concentrations of VOCs during the months when control measures were in effect. The typical bimodal O 3 pattern was eliminated during CP along with the absence of peak VOC levels between 10:00 Hrs and 16:00 Hrs, which surpassed the level of 40 μg/m3 during NCP. The analyses of O 3 formation potential (OFP) and rate of loss of OH radicals (L OH) indicated that alkenes and aromatics were the most chemically active VOCs driving the production of O 3. Following six types of sources were determined for VOCs using positive matrix factorization (PMF): (1) solvent use (8.2%); (2) fuel evaporation (25.1%); (3) petrochemical plant (17.3%); (4) LPG (20.1%); (5) industrial process (16.1%); (6) vehicular emissions (13.2%). Emissions from vehicles and solvent use declined by 19.21% and 15.43%, respectively, underscoring their importance as controllable VOC sources in Shanghai, China. Overall, the study demonstrated the effectiveness of regional control measures in improving air quality by reducing the production of O 3 and related VOCs. [Display omitted] • Characteristics and sources of VOCs in industrial parks in Shanghai were analyzed under different management periods. • Industrial process and vehicle exhaust were major sources of VOCs. • Controlling the emissions of alkenes and aromatics was crucial for mitigating regional ozone pollution. • Control measures in the summer of 2022 effectively reduced the VOCs emission. [ABSTRACT FROM AUTHOR]

Ground-level ozone (O 3) poses a significant threat to food security in China. Therefore, it is imperative to conduct a comprehensive scientific evaluation of the potential hazards posed by O 3 to agricultural crops. This study continuously observed variation in meteorological factors, O 3 concentration, O 3 deposition rate and flux, and quantified the distribution characteristics of O 3 deposition flux in stomatal and non-stomatal pathways. Results suggested that the O 3 dry deposition rate and flux in winter wheat fields exhibited relatively stable variations at night but pronounced fluctuations during the day. Their mean values were 0.31 cm s−1 and -0.0044 μmol m−2·s−1, respectively, with peak values occurring at 08:30 and 14:00. The cumulative O 3 total flux during the main growth season of winter wheat was 26.1 mmol m−2, with stomatal and non-stomatal fluxes accounting for 7.7 mmol m−2 and 18.4 mmol m−2, respectively. The proportions of total O 3 flux in stomatal and non-stomatal channels were 29.5% and 70.5%, respectively, with daytime proportions being 39.7% and 60.3%, respectively. These findings provide crucial insights for future accurate assessments of crop yield loss due to O 3 at the earth's surface. [Display omitted] • Advanced eddy covariance techniques were used for O 3 flux observations in China. • Continuous O 3 flux was obtained for the first time in a wheat field in eastern China. • O 3 deposition flux and rate were 0.31 cm s−1 and -0.0044 μmol m−2·s−1, respectively. • Non-stomatal deposition in O 3 played a dominant role in the dry deposition process. [ABSTRACT FROM AUTHOR]

Ground-level ozone (O 3) pollution is a major air quality issue in densely populated urban areas. Despite a significant decline in human activities in the megacity Shanghai from March 28 to May 31, 2022, ground-level measurements indicate a rise in maximum daily average 8-h (MDA8) O 3 concentrations in comparison to the corresponding period in 2021. There is a need for quantitative analysis to identify the reasons behind this increasing O 3 concentration. We analyzed ground measurements of O 3 and its precursors and meteorological parameters made in Shanghai, using random-forest (RF) model and chemical box model to elucidate the roles of meteorological and chemical factors in influencing O 3 concentrations. Across urban, suburban, semi-rural, and coastal sites, the urban center of Shanghai experienced the largest decreases in the concentrations of nitrogen oxides (NO x ; 53%) and volatile organic compounds (VOCs; 52%), with the most notable rise in MDA8 O 3 concentrations (16%). RF modeling indicates that meteorological factors reduced MDA8 O 3 concentrations by a marginal 3%, whereas a decline in anthropogenic emissions resulted in a 17% increase in MDA8 O 3 concentrations. Chemical box modeling at the Pudong urban site indicates that while the decline in VOCs reduced O 3 production by 42%, this was negated by a reduction in NO x from traffic emissions, which enhanced O 3 production by 51%, resulting in an increase in O 3 production overall. Despite a halving in precursor levels, Shanghai's urban centre remains predominately under VOC-limited conditions throughout the study period, with high NO 2 levels from the petrochemical industry and traffic emissions. Joint control of anthropogenic VOCs (AVOCs) and NO x , with a ratio greater than 1.29, could help avoid exacerbation of O 3 pollution and reduce NO 2 pollution. Our findings emphasize the necessity of reducing industrial emissions along with ongoing green transportation strategies for alleviating O 3 pollution in megacities like Shanghai. • Emission reductions drove an O 3 increase in Shanghai during the 2022 lockdown. • Shanghai's urban centre remains predominately under VOC-limited conditions. • The high NO 2 level was attributed to petrochemical industry and traffic emissions. [ABSTRACT FROM AUTHOR]

Reducing ozone in the New York City (NYC) region requires understanding the nonlinearity of ozone production (PO 3) and its sensitivity to volatile organic compounds (VOCs) and nitrogen oxides (NO x = NO 2 + NO). Using observations from the Long Island Sound Tropospheric Ozone Study (LISTOS) in the late spring and summers of 2017–2019 and a 0-D box model, we test the sensitivity of PO 3 to ozone precursors. PO 3 is greater in the morning than the afternoon due to increased concentrations of NO 2 and VOC. This diurnal variation in PO 3 is enhanced in the late summer. Based on the model response of PO 3 to changes in initial NO 2 , 14% of samples are within a VOC-limited regime. The metric LRO x /LNO x , which compares the radical loss rates via self-reaction to their reaction with NO 2 , indicates an additional 17% of samples are in transition between NO x and VOC-limited regimes (0.30 <= LRO x /LNO x <= 1). We often find PO 3 to be VOC-limited in NYC and along the Connecticut coastline (I-95 corridor). In these samples, PO 3 is most sensitive to isoprene, propene, and isopentane, and individual VOCs have strong diurnal and seasonal variations. We further compare PO 3 calculations using the near explicit Master Chemical Mechanism (MCMv3.3.1) and Carbon Bond 6 revision 2 (CB6r2) for a more direct link to regulatory air quality models. Modeled PO 3 is 20% greater in MCMv3.3.1, due largely to the speciation of VOC and organic peroxy radicals, however the bounds of LRO x /LNO x used to determine the transition range between PO 3 regimes remain the same. • Ozone production is faster in the morning than in the afternoon. • VOC-limited ozone production is frequent along the Connecticut coastline and in NYC. • Ozone production sensitivity to biogenic and anthropogenic VOC varies with season and time of day. • Greater ozone production is calculated using MCMv3.3.1 compared to CB6r2, though both exhibit similar NO x sensitivity. [ABSTRACT FROM AUTHOR]

This study presents the validation of total column ozone (TCO) data retrieved from the Geostationary Environment Monitoring Spectrometer (GEMS) against ground-based Pandora spectrometer observations during the GEMS Map of Air Pollution (GMAP) campaign from November 2020 to January 2021 in Seosan, South Korea. To evaluate the accuracy of the Pandora TCO measurements obtained during the campaign period, all Pandora instruments were installed at the Seosan supersite for intercomparison analysis. Subsequently, the instruments were relocated to four sites for direct sunlight measurements. The Pandora instruments exhibited a high degree of consistency with an average difference of 0.5 ± 1.0 DU. This study demonstrated that accurate comparison of ground-based ozone measurements with satellite ozone measurements depended on the threshold values set for the spatial and temporal alignment of the two datasets and the size of the satellite footprint and viewing angle. The comparison of the GEMS, TROPOspheric Monitoring Instrument (TROPOMI), and Ozone Mapping and Profiler Suite Nadir Mapper (OMPS) satellite TCO with the Pandora TCO showed high agreement across measurements. However, a distinct downward trend was observed in the Mean Bias (MB) for GEMS from December–January, indicating an issue with the GEMS Level 1C irradiance. The validation using hourly Pandora data demonstrated GEMS capability to monitor daily ozone variations but with a bias of approximately −1% to −2.6% compared with that of Pandora. • Pandora instruments were deployed to generate ground validation data for GEMS total column ozone during GMAP campaign. • Comparing GEMS, TROPOMI, and OMPS with Pandora revealed strong agreement with substantially low mean bias for GEMS–Pandora. • GEMS daily total ozone observation can effectively capture the variations evaluated by using Pandora. [ABSTRACT FROM AUTHOR]

The O 3 photochemical indicator is a tool used to identify the sensitive precursors of O 3 formation. Establishing a reliable photochemical indicator and its transition value composed of continuous automatic monitoring of chemical components can not only analyze sensitive precursors of O 3 formation in real-time but also analyze the time and space distribution characteristics of sensitive precursors of O 3 formation at a relatively lower cost. Among the photochemical indicators that are often mentioned at present, the ratio of ozone to nitrogen oxides (O 3 /NOx, O 3 /NO Z , and O 3 /NO Y) should have the greatest potential for continuous monitoring. This study used the Community Multiscale Air Quality Modeling System to evaluate whether these three indicators are applicable to environmental conditions in Taiwan. Research results show that the indicator O 3 /NO Z was less suitable for Taiwan, while the indicator O 3 /NO Y (transition value = 5.3) and the indicator O 3 /NOx (transition value = 29.3) could more accurately evaluate the ozone sensitivity of Taiwan's overall grid, and had no obvious bias in judging the ozone sensitivity of rural and urban grids. This study also found that it is not appropriate to directly use the photochemical indicator transition values from the literature. Usually, because the value is too high or too low, there is an obvious bias in judging the ozone sensitivity of rural and urban grids. This result also demonstrates the need to consider local meteorological and emission conditions when estimating transition values of photochemical indicators. In addition, when using the photochemical indicator O 3 /NO Y , attention should be paid to the calculation of NO Y species composition. The more complete the NO Y composition, the better its ability to correctly judge ozone sensitivity. • The transition values of photochemical indicators that can be continuouslymonitored were estimated. • The capabilities of the photochemical indicators with different NO Y composition and transition values were compared. • The transition value estimated for O 3 /NO X performed better in identifying O 3 precursor than that suggested in previous study. • The local weather and emission conditions should be taken into consideration when using photochemical indicators. [ABSTRACT FROM AUTHOR]

South America is underrepresented in research on air pollution exposure disparities by sociodemographic factors, although such disparities have been observed in other parts of the world. We investigated whether exposure to and information about air pollution differs by sociodemographic factors in the city of Rio de Janeiro, the second most populous city in Brazil with dense urban areas, for 2012–2017. We developed machine learning-based models to estimate daily levels of O 3 , PM 10 , and PM 2.5 using high-dimensional datasets from satellite remote sensing, atmospheric and land variables, and land use information. Cross-validations demonstrated good agreement between the estimated levels and measurements from ground-based monitoring stations: overall R 2 of 76.8 %, 63.9 %, and 69.1 % for O 3 , PM 2.5 , and PM 10 , respectively. We conducted univariate regression analyses to investigate whether long-term exposure to O 3 , PM 2.5 , PM 10 and distance to regulatory monitors differs by socioeconomic indicators, the percentages of residents who were children (0-17 years) or age 65+ years in 154 neighborhoods. We also examined the number of days exceeding the Brazilian National Air Quality Standard (BNAQS). Long-term exposures to O 3 and PM 2.5 were higher in more socially deprived neighborhoods. An interquartile range (IQR) increment of the social development index (SDI) was associated with a 3.6 μg/m3 (95 % confidence interval [CI]: 2.9, 4.4; p-value≤0.001) decrease in O 3 , and 0.3 μg/m3 (95 % CI: 0.2, 0.5; p-value = 0.010) decrease in PM 2.5. An IQR increase in the percentage of residents who are children was associated with a 4.1 μg/m3 (95 % CI: 3.1, 5.0; p-value≤0.001) increase in O 3 , and 0.4 μg/m3 (95 % CI: 0.3, 0.6; p-value = 0.009) increase in PM 2.5. An IQR increase in the percentage of residents age ≥65was associated with a 3.3 μg/m3 (95 % CI: 2.4, 4.3; p-value=<0.001) decrease in O 3 , and 0.3 μg/m3 (95 % CI: 0.1, 0.5; p-value = 0.058) decrease in PM 2.5. There were no apparent associations for PM 10. The association for daily O 3 levels exceeding the BNAQS daily standard was 0.4 %p–0.8 %p different by the IQR of variables, indicating a 7–15 days difference in the six-year period. The association for daily PM 2.5 levels exceeding the BNAQS daily standard showed a 0.7–1.5 %p difference by the IQR, meaning a 13–27 days difference in the period. We did not find statistically significant associations between the distance to monitors and neighborhood characteristics but some indication regarding SDI. We found that O 3 levels were higher in neighborhoods situated farther from monitoring stations, suggesting that elevated levels of air pollution may not be routinely measured. Exposure disparity patterns may vary by pollutants, suggesting a complex interplay between environmental and socioeconomic factors in environmental justice. • We developed hyper local estimates of daily PM 10 , PM 2.5 and O 3 levels. • PM 2.5 and O 3 levels were higher in more socially deprived neighborhoods. • PM 2.5 and O 3 levels were higher in neighborhoods with more children. • O 3 levels were higher in neighborhoods situated farther from monitoring stations. • Levels exceeded air quality standards in many neighborhoods without stations. [ABSTRACT FROM AUTHOR]

Ozone distribution and variation within the Planetary Boundary Layer (PBL) present challenges for air quality management. UAV-based ozone profile measurements offer advantages in terms of high vertical resolution throughout the PBL and flexibility. However, previous studies on vertical variation in the Pearl River Delta (PRD) region have rarely focused on measuring the vertical ozone variation during ozone pollution episodes. In this study, we integrated UAV-based monitoring, ground monitoring, and numerical modeling to investigate ozone variation, driving processes, and source regions of pollution episodic period. UAV-based observations during a 2021 ozone episode at rural areas in the PRD region revealed three ozone profiles: increasing, well-mixed, and decreasing with height. Morning profiles showed multiple layers influenced by meteorology, while peak ozone hours exhibited a well-mixed pattern. By integrating the validated numerical model, we found that chemical processes (CHEM) contributed positively to ozone episodes in both rural and urban scenarios, especially at the middle and upper PBL. Horizontal advection (HADV) significantly contributes to the episode in rural cases, while urban cases were significantly affected by vertical diffusion (VDIF). Backward trajectory and source apportionment analyses categorized PRD cities into upwind/non-upwind/local categories, showing ozone pollution originating from both upwind and non-upwind cities at different vertical levels. It is because wind shear influenced diverse source regions, and the transport channel for city-level ozone pollution exhibited daily and vertical changes. Moreover, it could also be contributed by the formed regional mixing ozone layer (ROM Layer) throughout the PBL during persistent ozone episodes, triggered by enhanced CHEM and significantly contributed by the VDIF. The ROM Layer at center cities, influencing ground-level ozone downwind through horizontal transport and vertical exchange. Considering the complex three-dimensional transport of ozone and the ROM Layer phenomenon, city-level management or regional co-control based on simple transport channels may be insufficient. Emissions control measures should cover all cities or target significant emitters to address regional ozone pollution. [Display omitted] • Vertical ozone variation during an episode was successfully captured by UAV and applied to model validation. • The regional ozone could be vertically well mixed at different levels includes local, upwind, and non-upwind sources. • The transport channel may not be well represented by single-layer wind pattern, it may have complex 3D structure. • For persistent ozone episode, the source contribution from non-upwind cities is also critical for city pollution level. • A regional ozone mixing layer (ROM Layer) was found and raises challenge on emission control of co-prevention and co-control strategies. [ABSTRACT FROM AUTHOR]

Tropospheric ozone (O 3) is an important air pollutant with a significant impact on human health, agricultural crops, ecosystems, and global warming. In the Greater Bay Area (GBA), O 3 pollution concentration has shown an increasing trend in the last decade. It has become crucial to gain a deeper understanding of the factors contributing to this phenomenon. This study deployed a sensor network with high spatial-temporal resolution measurement of O 3 and its key precursors in mid-November 2022 during a severe O 3 episode. The spatial-temporal characteristics and contributions of local generation and regional transport were analyzed based on clustering methodology. The regional distribution and possible sources were also discussed in combination with the NAQPMS model and the HYSPLIT model. The results indicated that the O 3 episode was dominated by local generation while regional transport contributed to an average of 20 ppb in the GBA region, under the influence of sea-land winds and low-level anticyclones. Guangzhou showed the most severe O 3 pollution, with a maximum hourly concentration near 120 ppb, followed by Zhongshan, Dongguan, etc. The O 3 pollution of Hong Kong and Macau showed faster dispersion and less accumulation during the daytime. The O 3 concentrations of Huizhou and Jiangmen were the lowest, but the nighttime O 3 accumulation was close to 40 ppb during the episode. The study demonstrated ad-hoc deployment of high-density sensor networks is an effective tool to study the formation and transport of O 3 during episodic days with synoptic approaches by ad-hoc high-density sensor network measurement and combination of modeling tools. • A high O 3 episode was monitored by high-density ad-hoc sensor network in the Greater Bay Area (GBA) in November 2016. • The spatial-temporal characteristics and the contributions of local formation and regional transport were focused on the analysis. • This O 3 episode was mainly impacted by local generation, with only around 20 % coming from regional contribution. • High concentrations of O 3 precursors emissions and the favorable meteorological conditions were the main factors contributing to O 3 pollution in GBA. [ABSTRACT FROM AUTHOR]

Surface ozone pollution is a significant environmental problem. In addition to the control of ozone precursors, direct catalytic decomposition of ozone is an effective control method with broad prospects. At present, the evaluation of the ozone decomposition performance of catalysts is typically performed in the laboratory, and the lack of scientific evaluation means to apply them to complex ambient atmosphere limits the practical application of ozone removal catalysts. Here, we devised a new evaluation method for ozone catalytic decomposition materials in the ambient atmosphere that can comprehensively evaluate the influence of various factors in the ambient atmosphere on performance. The results showed that ozone catalytic decomposition materials can maintain a decomposition efficiency of more than 20% in ambient atmosphere. The decomposition efficiency is mainly affected by distance, the closer the distance; the higher the decomposition efficiency. In addition, the concentration of ozone in the environment also affects the decomposition efficiency and shows a positive correlation. As the ozone concentration increased, the decomposition efficiency increased. An increase in relative humidity can cause a decline in decomposition efficiency, but this effect is eliminated with a decrease in humidity. In addition, the ozone catalytic decomposition materials can reduce the ozone concentration in the environment from 160 μg/m3to less than 100 μg/m3, which can play a great role in environmental ozone pollution control. [Display omitted] • We established the test of ozone decomposition materials in ambient atmosphere. • Ozone decomposition materials can maintain 20% average purification efficiency. • We discussed the effects of distance, ozone concentration, and relative humidity. [ABSTRACT FROM AUTHOR]

High concentrations of surface ozone in urban and industrial regions worldwide have been a major air quality issue. Tehran, as the capital and the most populous city of Iran, has experienced intense ambient air pollution over the last three decades. This study aims to assess the long-term trends of ozone over this city in recent decades. Data series of maximum 8-h daily average (MDA8) ozone were obtained for the period between 2007 and 2021. To determine the MDA8 ozone trend attributed to the long-term changes in ozone precursor emissions, we isolated the effects of meteorology and short-term ozone variability. The results show a downward trend from 2007 to 2014 (P1) and an upward trend from 2014 onward (P2). The long-term precursor emissions changes contribute to a 29.1% negative trend (=−0.7 ppb year−1) over P1 and an 8.95% upward trend (=0.1 ppb year−1) over P2. To find the causes of the trend transition, we investigated the relationship between the adjusted MDA8 and several ozone precursors, namely NO x and CO. It is found that, over P1, the dominant chemistry regime is mixed, in which the decline of CO and NO x (attributed to industrial sources) is associated with the downward trend of ozone. On the other hand, the upward trend of ozone over P2 is associated with an increase in NO x mostly attributed to road transport (passenger cars) and residential sectors. • Surface ozone trend over the megacity of Tehran in the last decade is derived. • The influences of meteorology and short-term variability on the trend are minimized. • A transition point in the ozone trend attributable to road transport is found. [ABSTRACT FROM AUTHOR]

This study analyzed the impact of shipping emissions on ozone (O 3) concentrations in East Asia during the Korea-United States Air Quality (KORUS-AQ) and the Satellite Integrated Joint monitoring for Air Quality (SIJAQ) 2021 campaign period. Numerical simulations were performed during the KORUS-AQ (May 2016, the KORUS case) and the SIJAQ 2021 (October–November 2021, the SIJAQ case) using Community Multi-scale Air Quality (CMAQ), the three-dimensional chemical transport model. We additionally simulated an experiment without shipping emissions to compare the impact with and without shipping emissions. Using the validated simulation results, the average O 3 concentrations in inland regions were found to be 35.63 ppb and 20.62 ppb in the KORUS and SIJAQ cases, respectively. The average O 3 concentrations were higher in the KORUS case owing to the difference in weather conditions between the two cases in various seasons. The results of examining the impact of shipping emissions on O 3 concentrations in the ocean area indicate that both the KORUS and SIJAQ cases resulted in a decrease in O 3 concentrations in the Yellow Sea region, while the O 3 concentrations increased in the East Sea and North Pacific regions. In particular, in the Yellow Sea and East China Sea, where the O 3 concentrations decreased in the KORUS case, O 3 sensitivity results showed volatile organic compounds (VOC)-sensitive regime when the shipping emissions were removed but changed to nitrogen oxide (NO x)-sensitive regime when the shipping emissions were added. Meanwhile, in the inland regions, the SIJAQ case decreased O 3 concentrations in most areas, whereas the KORUS case showed an increase in O 3 concentrations in the Korean Peninsula and Japan. Analysis of O 3 sensitivity revealed that the regions of the Korean Peninsula and Japan, where O 3 concentrations increased, exhibited a NO x -sensitive regime. Particularly, in the case of the Korean Peninsula, the initial transport of shipping emissions in the western part led to a decrease in O 3 concentrations. However, as shipping emissions were further transported from west to east, they became more diluted, and additional NO x generated by O 3 titration reactions was also transported, gradually increasing O 3 concentrations. Furthermore, we found that during seasons with abundant BVOC emissions, the transport of shipping emissions could contribute to additional O 3 production. These results confirmed that shipping emissions in East Asia primarily reduce O 3 concentrations, however, differences in seasonal and regional O 3 sensitivity and transportation patterns can contribute to O 3 production. [Display omitted] • O 3 concentration changes in the East Asian regions due to ocean emissions during the KORUS-AQ and SIJAQ campaign periods are investigated. • The influence of ocean emissions on the production and loss of O 3 varies by region and season. • The ocean emissions could result in the transition of the O 3 sensitivity regime in some ocean areas. • The seasonal transport of ocean emissions to BVOC-rich inland regions can contribute to the increase in O 3 concentration. [ABSTRACT FROM AUTHOR]

While concentrations of most air pollutants have been decreasing in Europe over the last 20 years, O 3 is showing variable trends, with increasing average and decreasing peak concentrations. The complexity of O 3 chemistry adds to the difficulty of understanding both the trends observed and how concentrations can be mitigated. This paper tries to answer the following questions: which emission sectors should be targeted and what levels of reduction could be achieved? To address these reflections, an Atlas of O 3 chemical regimes has been constructed. For this Atlas, 22 European cities were selected and the surrogate model Air Control Toolbox (ACT) was used to evaluate the simulated changes in several ozone metrics as a result of reductions in road transport and industrial emissions. O 3 chemical regimes have been classified and put in perspective with meteorological and emission data at each city location and around. The O 3 sensitivity to road transport and industrial emissions differ from one city to another, but also for the same city when considering different ozone metrics and seasons (e.g., annual means versus SOMO35 or summer peaks). Counterproductive impacts yielding O 3 increase when emissions are reduced are mainly encountered in regions or periods where O 3 concentration are relatively low. In terms of meteorological factors, O 3 chemical regimes are mostly impacted by the amount of solar radiation received but wind speed also has a considerable impact. Most cases show a higher sensitivity to emission reductions from road transport or equal sensitivity to emission reductions from road transport and industry. Very few cases are more sensitive to emissions from the industrial sector. However, the response of annual or seasonal average O 3 metrics to industrial and road transport emissions can be considered relatively low with a maximum reduction of 33% for a 100% reduction of both industrial and road transport emissions. This is because anthropogenic emission can only mitigate ozone above a substantial natural tropospheric background. It is precisely this incremental anthropogenic ozone, which should be targeted by efficient policies as we also demonstrate that none of the cities studied would exceed the European target value with a 100% reduction in emissions. • An atlas of ozone chemical regimes has been constructed for 22 European cities. • O 3 sensitivity to road transport and industrial emissions differ when considering different ozone metrics and different periods of the year. • Counterproductive effects of precursors emission reductions on ozone are a concern where and when ozone concentrations are low. • On the contrary, significant reductions of precursor emissions are found to reduce the number of exceedances of the EU target limit value. • In most cities, mitigation of road transport yields larger benefit to ozone air pollution than mitigation of the industrial sector. [ABSTRACT FROM AUTHOR]

Just under three hundred thousand hourly O 3 observations from the Mace Head, Ireland atmospheric monitoring station have been assembled into a complete dataset covering the thirty five-year period from April 1, 1987 through to May 31, 2022. Of these, seventy thousand hourly observations were assigned to baseline air masses over the 422 months in the study. Annual mean baseline mixing ratios rose from 34 ppb in 1988 to a peak of 42 ppb in 1999 before declining to 39 ppb in 2021. Monthly mean baseline mixing ratios reached a peak of 53 ppb in April 1999. Baseline O 3 mixing ratios exhibit a marked seasonal cycle, with maxima in April and minima in August. A detailed examination of the differences between the baseline and complete monthly mean O 3 mixing ratios revealed a set of monthly differences with some striking long-term changes. Wintertime differences were dominated by a series of O 3 depletion events in which, during the early years of the study, reduced ozone to near zero in long-range transport events. European NO x emission reductions have reduced significantly the number and severity of these wintertime O 3 depletion events. Summertime differences were dominated by a series of regional photochemical episodes. In the early years of the record, the regional photochemical episodes were intense enough to raise the monthly means in the complete record above the baseline means. European volatile organic compound (VOC) and NO x precursor emission reductions have dramatically reduced the number and intensity of these events. Episodic peak O 3 levels have also fallen steadily as a result of concerted, European action on regional VOC and NO x emissions. Subsets of the baseline and complete ozone datasets between 2017 and 2022 were scrutinised for possible COVID-19 impacts. Baseline ozone levels were lower than expected during 2020 and 2021 but the statistical significance of these impacts is difficult to judge, and reduced stratosphere-troposphere exchange rather than COVID-19 emission reductions may be the cause. • 35 years of ozone observations for Mace Head, Ireland are presented. • Northern hemisphere baseline ozone levels have increased, levelled off and begun to decline. • COVID-19 impact is small but detectable. • European NO x and VOC emission controls have reduced wintertime ozone depletion and summertime photochemical production. [ABSTRACT FROM AUTHOR]

The chemical loss of volatile organic compounds (VOCs) is influenced by atmospheric and is closely related to the photochemical formation of ozone (O 3). Therefore, research on the atmospheric chemical transformation of VOCs is essential to understand their contribution to O 3 formation. This study collected data on photochemical-related atmospheric components and meteorological factors in spring at a typical comprehensive observation platform in Guangzhou, China. The photochemical age method was used to evaluate the loss of VOCs due to atmospheric photochemical transformation and to analyze the contribution of such transformation to the source apportionment of VOCs and to the ozone formation potential (OFP). The results show that the mean photochemical loss of total volatile organic compounds (TVOCs) during the observation period was 4.1 ppbv, accounting for approximately 15% of the initial TVOC content. Alkenes had the highest consumed concentration/initial concentration (C/I ratio) of 37.3%. A comparison of the source apportionment results obtained using observational positive matrix factorization (Ob-PMF) and in situ positive matrix factorization (In-PMF) revealed that photochemical losses significantly affected VOCs emitted from industrial and biological sources. Furthermore, neglecting the photochemical loss of VOCs in PMF source apportionment could lead to an underestimation of the contribution of VOCs from industrial and biological sources. The calculated values of OFP under VOC loss (OFP C – VOCs) showed that OFP C-VOCs constituted approximately 30% of the OFP of the initial VOCs. 93.2% of the OFP was attributed to the photochemical loss of alkenes and aromatic hydrocarbons, indicating their significant influence on O 3 formation. This study emphasizes the importance of fully considering the photochemical loss of VOCs for accurately assessing their sources and contributions to ozone pollution. It also provides theoretical support for formulating VOC emission reduction strategies in the Pearl River Delta region. [Display omitted] • The impact of photochemical loss on the source apportionment of VOCs and O 3 formation were investigated. • The photochemical loss of alkenes constituted the largest proportion (37.31%). • VOCs from industrial emissions were notably influenced by photochemical loss. • The OFP of initial VOCs was underestimated by ca. 30% due to the photochemical loss of VOCs. [ABSTRACT FROM AUTHOR]

In summer, frequent ozone (O 3) episodes occur in New York City (NYC) and coastal areas along Long Island Sound (LIS) due to complex interplay of urban pollutants transport, land-sea breezes, and chemistry. The Long Island Sound Tropospheric Ozone Study (LISTOS) was carried out to address this issue; here we present an integrated analysis of the diurnal variation of planetary-boundary-layer height (PBLH) and O 3 in the NYC urban and coastal area during LISTOS in summer 2019. A persistent O 3 episode (July 28–31, 2019) is investigated which shows much higher O 3 (90–120 ppb with 5-min average maximum) along the North-shore of Long Island (NLI) than the NYC urban and South-shore of Long Island (SLI). We evaluate the PBLH estimate with a multi-platform observation in the complex coastal environment, and compare the PBLH diurnal variation in the NYC urban to coastal areas. The results indicate lower PBLH in the mid-morning and noon in the NLI than the NYC urban area. With the simultaneously measured O 3 and PBLH, the integrated O 3 content or total content in the PBL defined as the O 3 concentrations multiplied by PBLH show good consistency in the urban and NLI coast at noon on July 28–29, 2019. A dense O 3 plume, rich in CO, aerosols, black carbon, HCHO and NOx appeared in the PBL as detected from the UMD Cessna research aircraft, satellite TROPOMI and ozonesonde; their coincidently large values imply the combined effects of urban plumes transport, lower PBLH and land-sea breezes in the NLI area. Finally, we evaluated the forecast of O 3 and PBLH from the NOAA NAM-CMAQ (12 km grid) and WRF-Chem (1.3 km grid) models with the observations. Both models show good agreement with the observations at the NYC urban site; but at the NLI coastal site, the NAM-CMAQ model forecast indicates a timing bias for the maximum O 3 at noon. These results provide insight into the impacts of the sea breeze and urban heat island on air quality. [Display omitted] • Examine PBLH estimate with different platform/methods in NYC urban and coastal area. • Compare diurnal variation of PBLH and O 3 in the urban and coastal area. • Indicate O 3 -rich plume in the coastal area due to urban transport, sea breezes and low PBL. • Identify a model forecast bias on the timing of maximum O 3 and PBLH in the coastal area. [ABSTRACT FROM AUTHOR]

Recent studies predict that ozone (O 3) concentrations within major California cities in the year 2050 will continue to violate the 8-h O 3 standard despite the adoption of low-carbon energy. This O 3 penalty largely stems from persistent NOx-rich chemistry within urban cores that causes O 3 concentrations to increase when traditional combustion sources are replaced by renewable energy sources. Here we employ a Chemical Transport Model (CTM) equipped with a novel O 3 source apportionment technique to better understand O 3 formation and to design supplemental control measures to complement Greenhouse Gases (GHG) reduction strategies in California. Two base scenarios were analyzed: (i) a 2050 "business-as-usual" (BAU) scenario with O 3 violations on 43% of simulated days, and (ii) a 2050 Greenhouse Gases reduction (GHGAi) scenario with O 3 violations on 32% of simulated days. The source apportionment results of the GHGAi scenario identified offroad equipment & rail, marine vessels & aircraft, and industrial & agricultural emissions as the major NOx sources that contributed to the O 3 violations, while boundary conditions & initial conditions (BCIC) and biogenic emissions were identified as the major volatile organic compounds (VOCs) sources. Despite a HCHO/NO2 ratio (FNR) suggesting that the SoCAB is in a VOC-limited chemical regime, the major VOC sources that contribute to O 3 formation are not controllable. Therefore, complementary O 3 control strategies are proposed that focus on NOx emissions within the GHGAi scenario. Three cumulative Supplemental Control Steps were evaluated. Control Step I reduced emissions from off-road equipment & rail, and marine vessels & aircraft (65% NOx emissions reduction relative to GHGAi). Control Step II expanded the measures in Control Step I by reducing emissions from industrial and agricultural sources (cumulative 73.6% NOx emissions reduction relative to GHGAi), while Control Step III extended the amount of control applied to all sources covered in Control Steps I and II (cumulative 85.4% NOx emissions reduction relative to GHGAi). All three Control Steps lowered O 3 concentrations significantly in the SoCAB, with residual O 3 violations mainly predicted in non-populated wilderness areas. The significant reductions in O 3 produced by the Supplemental Control Steps decreased the predicted incidence of hay fever/rhinitis, asthma, and all-cause mortality by an order of magnitude compared to the transformation from the BAU to GHGAi scenario. The predicted public health savings associated with the Supplemental Control Steps are valued at $19.70–30.36B/yr. • O 3 violations will continue in Los Angeles even after adoption of low carbon fuels. • VOC sources that contribute to future O 3 formation are not practical to control. • Additional NOx reductions of 80% may be needed to reduce O 3 to safe levels. • Public health benefits from aggressive NOx control are $30B/yr. [ABSTRACT FROM AUTHOR]

While it is well known that combustion of ethanol as a biofuel will lead to enhanced emissions of methane, ethene (ethylene), acetaldehyde, formaldehyde, and oxides of nitrogen (primarily NO) when compared to gasoline alone, especially during cold starts or if catalytic converters are not operating properly, the impacts of increases in atmospheric ethene levels from combustion of fuels with higher ethanol content has not received much attention. Ethene is a well known and potent plant growth hormone and exposure to agricultural crops and natural vegetation results in yield reductions especially when combined with higher levels of PAN and ozone also expected from the increased use of ethanol/gasoline blends. We report here some baseline measurements of ethene obtained in 2002 in the southwestern and south central United States. These data indicate that current ethene background levels are less than 1 ppb. Anticipated increases in fuel ethanol content of E30 or greater is expected to lead to higher atmospheric levels of ethene on regional scales due to its atmospheric lifetime of 1.5-3 days. These background measurements are discussed in light of the potential enhancement of ethene levels expected from the anticipated increases in ethanol use as a renewable biofuel. © 2012 Elsevier Ltd.

Hourly measurements of O3, NO, NO2, PAN, HNO3 and NOy concentrations, and eddy-covariance fluxes of O3 and NOy over a temperate deciduous forest from June to November, 2000 were used to evaluate the dry deposition velocities (Vd) estimated by the WRF-Chem dry deposition module (WDDM), which adopted Wesely (1989) scheme for surface resistance (Rc), and the Noah land surface model coupled with a photosynthesis-based Gas-exchange Evapotranspiration Model (Noah-GEM). Noah-GEM produced better Vd(O3) variations due to its more realistically simulated stomatal resistance (Rs) than WDDM. Vd(O3) is very sensitive to the minimum canopy stomatal resistance (Ri) which is specified for each seasonal category assigned in WDDM. Treating Sep-Oct as autumn in WDDM for this deciduous forest site caused a large underprediction of Vd(O3) due to the leafless assumption in 'autumn' seasonal category for which an infinite Ri was assigned. Reducing Ri to a value of 70sm-1, the same as the default value for the summer season category, the modeled and measured Vd(O3) agreed reasonably well. HNO3 was found to dominate the NOy flux during the measurement period; thus the modeled Vd(NOy) was mainly controlled by the aerodynamic and quasi-laminar sublayer resistances (Ra and Rb), both being sensitive to the surface roughness length (z0). Using an appropriate value for z0 (10% of canopy height), WDDM and Noah-GEM agreed well with the observed daytime Vd(NOy). The differences in Vd(HNO3) between WDDM and Noah-GEM were small due to the small differences in the calculated Ra and Rb between the two models; however, the differences in Rc of NO2 and PAN between the two models reached a factor of 1.1-1.5, which in turn caused a factor of 1.1-1.3 differences for Vd. Combining the measured concentrations and modeled Vd, NOx, PAN and HNO3 accounted for 19%, 4%, and 70% of the measured NOy fluxes, respectively. © 2011 Elsevier Ltd.

The year 2000 radiative forcing (RF) due to changes in O3 and CH4 (and the CH4-induced stratospheric water vapour) as a result of emissions of short-lived gases (oxides of nitrogen (NOx), carbon monoxide and non-methane hydrocarbons) from three transport sectors (ROAD, maritime SHIPping and AIRcraft) are calculated using results from five global atmospheric chemistry models. Using results from these models plus other published data, we quantify the uncertainties. The RF due to short-term O3 changes (i.e. as an immediate response to the emissions without allowing for the long-term CH4 changes) is positive and highest for ROAD transport (31 mW m−2) compared to SHIP (24 mW m−2) and AIR (17 mW m−2) sectors in four of the models. All five models calculate negative RF from the CH4 perturbations, with a larger impact from the SHIP sector than for ROAD and AIR. The net RF of O3 and CH4 combined (i.e. including the impact of CH4 on ozone and stratospheric water vapour) is positive for ROAD (+16(±13) (one standard deviation) mW m−2) and AIR (+6(±5) mW m−2) traffic sectors and is negative for SHIP (−18(±10) mW m−2) sector in all five models. Global Warming Potentials (GWP) and Global Temperature change Potentials (GTP) are presented for AIR NOxemissions; there is a wide spread in the results from the 5 chemistry models, and it is shown that differences in the methane response relative to the O3 response drive much of the spread.

A photochemical trajectory model (PTM), coupled with the Master Chemical Mechanism (MCM) describing the degradation of 139 volatile organic compounds (VOCs) in the troposphere, was developed and used for the first time to simulate the formation of photochemical pollutants at Wangqingsha (WQS), Guangzhou during photochemical pollution episodes between 12 and 17 November, 2007. The simulated diurnal variations and mixing ratios of ozone were in good agreement with observed data (R2=0.80, P

A regional modeling system was applied with inputs from global climate and chemistry models to quantify the effects of global change on future biogenic emissions and their impacts on ozone and biogenic secondary organic aerosols (BSOA) in the US. Biogenic emissions in the future are influenced by projected changes in global and regional climates and by variations in future land use and land cover (LULC). The modeling system was applied for five summer months for the present-day case (1990-1999, Case 1) and three future cases covering 2045-2054. Individual future cases were: present-day LULC (Case 2); projected-future LULC (Case 3); and future LULC with designated regions of tree planting for carbon sequestration (Case 4). Results showed changing future meteorology with present-day LULC (Case 2) increased average isoprene and monoterpene emission rates by 26% and 20% due to higher temperature and solar insolation. However when LULC was changed together with climate (Case 3), predicted isoprene and monoterpene emissions decreased by 52% and 31%, respectively, due primarily to projected cropland expansion. The reduction was less, at 31% and 14% respectively, when future LULC changes were accompanied by regions of tree planting (Case 4). Despite the large decrease in biogenic emission, future average daily maximum 8-h (DM8H) ozone was found to increase between +8 ppbv and +10 ppbv due to high future anthropogenic emissions and global chemistry conditions. Among the future cases, changing LULC resulted in spatially varying future ozone differences of -5 ppbv to +5 ppbv when compared with present-day case. Future BSOA changed directly with the estimated monoterpene emissions. BSOA increased by 8% with current LULC (Case 2) but decreased by 45%-28% due to future LULC changes. Overall, the results demonstrated that on a regional basis, changes in LULC can offset temperature driven increases in biogenic emissions, and, thus, LULC projection is an important factor to consider in the study of future regional air quality. © 2009 Elsevier Ltd.

Air quality transcends all scales with in the atmosphere from the local to the global with handovers and feedbacks at each scale interaction. Air quality has manifold effects on health, ecosystems, heritage and climate. In this review the state of scientific understanding in relation to global and regional air quality is outlined. The review discusses air quality, in terms of emissions, processing and transport of trace gases and aerosols. New insights into the characterization of both natural and anthropogenic emissions are reviewed looking at both natural (e.g. dust and lightning) as well as plant emissions. Trends in anthropogenic emissions both by region and globally are discussed as well as biomass burning emissions. In terms of chemical processing the major air quality elements of ozone, non-methane hydrocarbons, nitrogen oxides and aerosols are covered. A number of topics are presented as a way of integrating the process view into the atmospheric context; these include the atmospheric oxidation efficiency, halogen and HOx chemistry, nighttime chemistry, tropical chemistry, heat waves, megacities, biomass burning and the regional hot spot of the Mediterranean. New findings with respect to the transport of pollutants across the scales are discussed, in particular the move to quantify the impact of long-range transport on regional air quality. Gaps and research questions that remain intractable are identified. The review concludes with a focus of research and policy questions for the coming decade. In particular, the policy challenges for concerted air quality and climate change policy (co-benefit) are discussed. © 2009 Elsevier Ltd.

A tethered balloon sampling system was used to measure vertical profiles of ozone, particles, and solar radiation in the atmospheric boundary layer on the northern edge of Mexico City, in March 2006 as part of the Megacity Impact on Regional and Global Environment-Mexico experiment. Several commercial sensors, designed for surface applications, were deployed on a tethered balloon platform. Profiles indicate that for these 3 scalars the boundary layer (surface up to 700 m) was well mixed in the period 10:00-16:00 LST. Good agreement was observed for median surface and balloon ozone and particle number concentrations. For most profiles, the surface deposition of ozone was not significant compared to median profile concentrations. Particle number concentration (0.3, 0.5, 1.0 and 5.0 μm) also showed little variation with attitude. Radiatprofiles showed a monotonic increase in diffuse radiation from the maximum altitude of profiles to the surface. Consequently, it was inferred that surface measurements of these likely were representative of lower boundary layer values during this time period. © 2009 Elsevier Ltd. All rights reserved.