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The persistent O 3 pollution in the Beijing-Tianjin-Hebei (BTH) region remains unresolved, largely due to limited comprehension of O 3 -precursor relationship and photochemistry drivers. In this work, intraday O 3 sensitivity evolution from VOC-limited (volatile organic compound) regime in the forenoon to transition regime in the late afternoon was inferred by relative incremental reactivity (RIR) in summer 2019 at Xianghe, a suburban site in BTH region, suggesting that VOC-focused control policy could combine with stringent afternoon NO x control. Then detailed impacts of VOC subgroups on O 3 formation were further comprehensively quantified by parametric OH reactivity (K OH ), O 3 formation potential (OFP), as well as RIR weighted value and O 3 formation path tracing (OFPT) approach based on photochemical box model. O 3 episode days corresponded to stronger O 3 formation, depicted by higher K OH (10.4 s -1 ), OFP (331.7 μg m -3 ), RIR weighted value (1.2), and F(O 3 )-OFPT (15.5 ppbv h -1 ). High proportions of isoprene and OVOCs (oxygenated VOCs) to the total K OH and the OFPT method were demonstrated whereas results of OFP and RIR-weighted presented extra great impacts of aromatics on O 3 formation. The OFPT approach captured the process that has already happened and included final O 3 response to the original VOC, thus reliable for replicating VOC impacts. The comparison results of the four methods showed similarities when utilizing K OH and OFPT methods, which reveals that the potential applicability of simple K OH for contingency VOC control and more complex OFPT method for detailed VOC- and source-oriented control during policy-making. To investigate propulsion of VOC-involved O 3 photochemistry, atmospheric oxidation capacity (AOC) was quantified by two atmospheric oxidation indexes (AOI). Both AOIp_G (7.0 × 10 7 molec cm -3 s -1 , potential AOC calculated by oxidation reaction rates) and AOIe_G (8.5 μmol m -3 , estimated AOC given redox electron transfer for oxidation products) were stronger on O 3 episode days, indicating that AOC promoted the radical cycling initiated from VOC oxidation and subsequent O 3 production. Result-oriented AOIe_G reasonably characterized actual AOC inferred by good linear correlation between AOIe_G and O 3 concentrations compared to process-oriented AOIp_G. Therefore, with continuous NO x abatement, AOIe_G should be considered to represent actual AOC, also O 3 -inducing ability., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

A series of emission reduction measures were conducted in Wuhan, Central China, to ensure good air quality during the 7th Military World Games (MWG) in October 2019. To better understand the implications for ozone (O 3 ) pollution control strategies, we applied integrated analysis approaches based on the de-weathered statistical model, parameterization methods, chemical box model, and positive matrix factorization model. During the MWG, concentrations of O 3 , NO x , and volatile organic compound (VOCs), OFP (O 3 formation potential), L OH (OH radical loss rate) were 83 µg/m 3 , 43 µg/m 3 , 26 ppbv, 188 µg/m 3 , and 3.9 s -1 , respectively, which were 26%, 18%, 3%, 15%, and 13% lower than pre-MWG values and 6%, 39%, 30%, 33%, and 50% lower than post-MWG values, respectively. After removing meteorological influence, O 3 and its precursors during the MWG decreased largely compared with post-MWG values, and only O 3 , NO 2 , and oxygenated VOCs (OVOCs) declined compared with pre-MWG values, which revealed the emission reduction measures during the MWG played an important role for O 3 decline. For six VOCs sources, the mass contributions of biomass burning and solvents usage during the MWG decreased largely compared with pre-MWG values. O 3 production was sensitive to VOCs and the key species were aromatics, OVOCs, and alkenes, which originated mainly from solvents usage, biomass burning, industrial-related combustion, and vehicle exhaust. Decreasing O 3 concentration during the strict control was mainly caused by OVOCs reduction due to biomass burning control. Generally, the O 3 abatement strategies of Wuhan should be focused on the mitigation of high-reactivity VOCs., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

To investigate the vertical distribution of volatile organic compounds (VOCs) concentrations in the Lhasa valley region, an intensive measurement campaign was first conducted in summer using a tethered balloon. The results showed that the average concentration of surface VOCs was 49.1 ± 30.1 ppbv, alkanes and aromatics were the main components. Notably, a very large discrepancy in VOCs was obtained between the wet (71.6 ± 25.9 ppbv) and dry (25.6 ± 8.0 ppbv) episodes, which was attributed to the atmospheric stability and diffusion capacity. Moreover, the total VOC (TVOCs) concentration declined under fluctuations, but it rapidly increased with height in the afternoon during the wet episode (2.50 ppbv/100 m, R 2  = 0.47). According to the PMF results, combustion was the dominant emission source, additionally, the contribution of solvent coating in the wet episode and the background in the dry episode increased with height. Moreover, the O 3 concentration increased with height, and the decrease in L NOx-OH could effectively prevent the occurrence of high O 3 values. This study indicated that low wind speeds and high humidity levels highly likely cause the accumulation of atmospheric VOCs under static and stable conditions, while the control of high O 3 concentrations must still greatly consider summertime NOx emissions in Lhasa., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Ozone pollution in 2019 in China is particularly severe posing a tremendous threat to the health of Chinese inhabitants. In this study, we constructed a more reliable and accurate 1-km gridded dataset for 2019 with as many sites as possible using the inverse distance weight interpolation method to analyze spatiotemporal ozone pollution characteristics and health burden attributed to ozone exposure from the perspective of different diseases and weather influence. The accuracy of this new dataset is higher than other public datasets, with the coefficient of determination of 0.84 and root-mean-square error of 8.77 ppb through the validation of 300 external sites which were never used for establishing retrieval methods by the datasets mentioned-above. The averaged MDA8 (the daily maximum 8 h average) ozone concentrations over China was 43.5 ppb, and during April-July, 83.9% of total grids occurred peak-month ozone concentrations. Overall, the highest averaged exceedance days (60 days) and population-weighted ozone concentrations (55.0 ppb) both concentrated in central-eastern China including 9 provinces (only 11.4% of the national territory); meanwhile, all-cause premature deaths attributable to ozone exposure reached up to 142,000 (54.9% of national total deaths) with higher deaths for cardiovascular and respiratory, and the provincial per capita premature mortality was 0.27~0.44‰. The six most polluted weather types in the central-eastern China are in order as follows: westerly (SW and W), cyclonic, northerly, and southerly (NW, N, and S) types, which accounts for approximately 73.2% of health burden attributed to daily ozone exposure and poses the greatest public health risk with mean daily premature deaths ranging from 466 to 610. Our findings could provide an effective support for regional ozone pollution control and public health management in China., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Under weak weather systems, pollutants circulate on plains and hillsides by means of oscillatory mountain-plain breezes (MPB). To investigate the impact of MPB on ambient volatile organic compounds (VOCs) on the northern edge of the North China Plain (NCP) region, synchronous online VOCs observations were first performed in the southwestern (Beijing, urban area) and northeastern (Xinglong, background area) of the dominant wind directions from September 11, 2020, to October 13, 2020. The results revealed that during the observation period, the average mixing ratios of TVOCs in Beijing and Xinglong were 32.5 ± 21.6 and 14.2 ± 8.6 ppbv, respectively, and a coincident temporal evolution trend of VOCs was observed at the two sites. Combined with the results of the backward trajectory, southerly air transport led to a significant increase in VOCs concentration, and southerly airflow was usually accompanied by apparent MPB circulation. Furthermore, the occurrence of MPB led to a sharp increase (1.5 times) in VOCs concentration in both Beijing and Xinglong. This study indicates that the periodic oscillation of the MPB leads to the large-scale pollution of "garbage out and garbage in", and the VOCs discharged by industry are the key to future control., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

High loads of ground-level ozone have occurred with the implementation of the Air Pollution Prevention and Control Action Plan. However, the long temporal variation in precursor nonmethane hydrocarbons (NMHCs) has rarely been studied. In this study, we examined the evolution of NMHCs in Beijing based on ambient measurements from 2000 to 2019. The results indicated that the annual variation of ambient NMHCs during 2000 and 2019 could be divided into two stages. The mixing ratios of NMHCs rapidly rose during 2000 and 2009 (1.76 ppbv/year) but exhibited a downward trend from 2009 to 2019 at rate of 0.80 ppbv/yr. Moreover, the notable decrease in alkenes and aromatics after 2009 led to a sharp decrease in the propylene-equivalent concentration (PEC) (-0.80 ppbv/year). Implementation of emission reduction measures in Beijing have effectively reduced the contribution of vehicle-related sources, but the contribution of solvent usage and fuel consumption increased, which will become the focus of VOC control in Beijing in the future., (Copyright © 2021. Published by Elsevier B.V.)

While extensive eddy covariance (EC) measurements of ozone (O 3 ) flux have been reported in American and European forests, such measurements in Asian forests are scarce. Here, we presented the first EC measurements of O 3 flux at two levels (above and below the canopy) in a Chinese forest. Above the canopy, O 3 always moved downward, with a maximum O 3 flux intensity of -15 ~ -10 nmol m -2 s -1 occurring at 9:00-14:00 LT and a maximum O 3 deposition velocity of 1.23 cm s -1 occurring at 9:00 LT; both of these values fell to nearly 0 at night. The O 3 deposition flux and O 3 deposition velocity below the canopy were both lower than those above the canopy. This discrepancy reached the maximum at 9:00-15:00 local time (LT), with the O 3 deposition flux and O 3 deposition velocity below the canopy being approximately 35 and 42% of those above the canopy, respectively. The O 3 flux was well correlated with the CO 2 flux and the latent heat flux, suggesting the important role of stomatal uptake in O 3 deposition. The O 3 deposition velocity increased with the increase in the air temperature, relative humidity, photosynthetically active radiation and friction velocity, but when these meteorological factors exceeded their optimum values, the increase in the O 3 deposition velocity tended to be flat. These findings advanced our understanding of the interactions between forests and the atmosphere. This unique dataset is also of great significance for the validation of relevant models concerned with the various impacts of the rapid increase in global O 3 concentrations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

To what extent anthropogenic emissions could influence volatile organic compound (VOCs) concentrations and related atmospheric reactivity is still poorly understood. China's 70th National Day holidays, during which anthropogenic emissions were significantly reduced to ensure good air quality on Anniversary Day, provides a unique opportunity to investigate these processes. Atmospheric oxidation capacity (AOC), OH reactivity, secondary transformation, O 3 formation and VOCs-PM 2.5 sensitivity are evaluated based on parameterization methods and simultaneous measurements of VOCs, O 3 , NO x , CO, SO 2 , PM 2.5 , JO 1 D, JNO 2 , JNO 3 carried out at a suburban site between Beijing and Tianjin before, during, and after the National Day holiday 2019. During the National Day holidays, the AOC, OH reactivity, O 3 formation potential (OFP) and secondary organic aerosol formation potential (SOAP) were 1.6 × 10 7 molecules cm -3 s -1 , 41.8 s -1 , 299.2 μg cm -3 and 1471.8 μg cm -3 , respectively, which were 42%, 29%, 47% and 42% lower than pre-National Day values and -12%, 42%, 36% and 42% lower than post-National Day values, respectively. Reactions involving OH radicals dominated the AOC during the day, but OH radicals and O 3 reactions at night. Alkanes (the degree of unsaturation = 0, (D, Equation (1)) accounted for the largest contributions to the total VOCs concentration, oxygenated VOCs (OVOCs; D ≤ 1) to OH reactivity and OFP, and aromatics (D = 4) to the SOAP. O 3 production was identified as VOCs-limited by VOCs (ppbC)/NOx (ppbv) ratios during the sampling campaign, with greater VOCs limitation during post- National Day and more-aged air masses during the National Day. The VOCs-sensitivity coefficient (VOCs-S) suggested that VOCs were more sensitive to PM 2.5 in low-pollution domains and during the National Day holiday. This study emphasizes the importance of not only the abundance, reactivity, and secondary transformation of VOCs but also the effects of VOCs on PM 2.5 for the development of effective control strategies to minimize O 3 and PM 2.5 pollution., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

An intensive and persistent regional ozone pollution event occurred over eastern China from 25 June to 5 July 2017. 73 out of 96 selected cities, most located in the Beijing-Tianjin-Hebei and the surrounding area (BTHS), suffered severe ozone pollution. A north-south contrast ozone distribution, with higher ozone (199 ± 33 μg/m 3 ) in the BTHS and lower ozone (118 ± 25 μg/m 3 ) in the Yangtze River Delta (YRD), was found to be dominated by the position of the West Pacific Subtropical High (WPSH) and mid-high latitude wave activities. In the BTHS, the positive anomalies of geopotential height at 500 hPa and temperature at the surface indicated favorable meteorological conditions for local ozone formation. Prevailing northwesterly winds in the mid-high troposphere and warm advection induced by weak southerly winds in the low troposphere resulted in low-moderate relative humidity (RH), less total cloud cover (TCC), strong solar radiation and high temperatures. Moreover, southerly winds prevailing over the BTHS aggravated the pollution due to regional transportation of O 3 and its precursors. On one hand, the deep sinking motion and inversion layer suppressed the dispersion of pollutants. On the other hand, O 3 -rich air in the upper layer was maintained at night due to temperature inversion, which facilitated O 3 vertical transport to the surface in the next-day morning due to elevated convection. Generally, temperature, UV radiation, and RH showed good correlations with O 3 in the BTHS, with rates of 8.51 (μg/m 3 )/°C (within the temperature range of 20-38°C), 59.54 (μg/m 3 )/(MJ/m 2 ) and -1.93 (μg/m 3 )/%, respectively., (Copyright © 2020. Published by Elsevier B.V.)

The structure of the boundary layer affects the evolution of ozone (O 3 ), and research into this structure will provide important insights for understanding photochemical pollution. In this study, we conducted a one-month observation (from June 15 to July 14, 2016) of the boundary layer meteorological factors as well as O 3 and its precursors in Luancheng County, Shijiazhuang (37°53'N, 114°38'E). Our research showed that photochemical pollution in Shijiazhuang is serious, and the mean hourly maximum and mean 8-hr maximum O 3 concentrations are 97.9 ± 26.1 and 84.4 ± 22.4 ppbV, respectively. Meteorological factors play a significant role in the formation of O 3 . High temperatures and southeasterly winds lead to elevated O 3 values, and at moderate relative humidity (40%-50%) and medium boundary layer heights (1200-1500 m), O 3 production sensitivity occurred in the transitional region between volatile organic compounds (VOC) and nitrogen oxides (NO x ) limitations, and the O 3 concentration was the highest. The vertical profiles of O 3 were also measured by a tethered balloon. The results showed that a large amount of O 3 was stored in the residual layer, and the concentration was positively correlated with the O 3 concentration measured the previous day. During the daytime of the following day, the contribution of O 3 stored in the residual layer to the boundary layer reached 27% ± 7% on average., (Copyright © 2019. Published by Elsevier B.V.)

Understanding the formation of tropospheric ozone (O 3 ) and secondary particulates is essential for controlling secondary pollution in megacities. Intensive observations were conducted to investigate the evolution of O 3 , nitrate (NO 3 - ), sulfate (SO 4 2- ) and oxygenated organic aerosols ((OOAs), a proxy for secondary organic aerosols) and the interactions between O 3 , NO x oxidation products (NO z ) and OOA in urban Beijing in August 2012. The O 3 concentrations exhibited similar variations at both the urban and urban background sites in Beijing. Regarding the O 3 profile, the O 3 concentrations increased with increasing altitude. The peaks in O 3 on the days exceeding the 1h or 8h O 3 standards (polluted days) were substantially wider than those on normal days. Significant increases in the NO z mixing ratio (i.e., NO y - NO x ) were observed between the morning and early afternoon, which were consistent with the increasing oxidant level. A discernable NO 3 - peak was also observed in the morning on the polluted days, and this peak was attributed to vertical mixing and strong photochemical production. In addition, a SO 4 2- peak at 18:00 was likely caused by a combination of local generation and regional transport. The OOA concentration cycle exhibited two peaks at approximately 10:00 and 19:00. The OOA concentrations were correlated well with SO 4 2- ([OOA]=0.55×[SO 4 2- ]+2.1, r 2 =0.69) because they both originated from secondary transformations that were dependent on the ambient oxidization level and relative humidity. However, the slope between OOA and SO 4 2- was only 0.35, which was smaller than the slope observed for all of the OOA and SO 4 2- data, when the RH ranged from 40 to 50%. In addition, a photochemical episode was selected for analysis. The results showed that regional transport played an important role in the evolution of the investigated secondary pollutants. The measured OOA and O x concentrations were well correlated at the daily scale, whereas the hourly OOA and O x concentrations were insignificantly correlated in urban Beijing. The synoptic situation and the differences in the VOC oxidation contributing to O 3 and SOAs may have resulted in the differences among the correlations between OOA and O x at different time scale. We calculated OOA production rates using the photochemical age (defined as -log 10 (NO x /NO y )) in urban plumes. The CO-normalized OOA concentration increased with increasing photochemical age, with production rates ranging from 1.1 to 8.5μgm -3 ppm -1 h -1 for the plume from the NCP., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Vertical ozone and meteorological parameters were measured by tethered balloon in the boundary layer in the summer of 2009 in Beijing, China. A total of 77 tethersonde soundings were taken during the 27-day campaign. The surface ozone concentrations measured by ozonesondes and TEI 49C showed good agreement, albeit with temporal difference between the two instruments. Two case studies of nocturnal secondary ozone maxima are discussed in detail. The development of the low-level jet played a critical role leading to the observed ozone peak concentrations in nocturnal boundary layer (NBL). The maximum of surface ozone was 161.7 ppbv during the campaign, which could be attributed to abundant precursors storage near surface layer at nighttime. Vertical distribution of ozone was also measured utilizing conventional continuous analyzers on 325-m meteorological observation tower. The results showed the NBL height was between 47 and 280 m, which were consistent with the balloon data. Southerly air flow could bring ozone-rich air to Beijing, and the ozone concentrations exceeded the China's hourly ozone standard (approximately 100 ppb) above 600 m for more than 12 h.

Continuous measurements of surface ozone (O3) and nitrogen oxides (NOX) at an urban site (39°37'N, 118°09'E) in Tangshan, the largest heavy industry city of North China during summertime from 2008 to 2011 are presented. The pollution of O3 was serious in the city. The daily maximum 1 h means (O3_1-hr max) reached 157 ± 55, 161 ± 54, 120 ± 50, and 178 ± 75 μg/m3 corresponding to an excess over the standard rates of 21%, 27%, 10%, and 40% in 2008-2011, respectively. The total oxidant level (OX = O3 + NO2) was high, with seasonal average concentrations up to 100 μg/m3 in summer. The level of OX at a given location was made up of NOX-independent and NOX-dependent contributions. The independent part can be considered as a regional contribution and was about 100 μg/m3 in Tangshan. Statistical early warning analysis revealed that the O3 levels would exceed the standard rate by 50% on the day following a day when the daily average ozone concentration (O3_mean) exceeded 87 μg/m3 and the daily maximum temperature (T_max) exceeded 29 °C. The exceed-standard rate would reach 80% when O3_mean and T_max exceeded 113 μg/m3 and 31 °C. Similarly, the exceed-standard rate would reach 100% when O3_mean and T_max exceeded 127 μg/m3 and 33 °C, respectively.

The measurement of SO(2), O(3), NO, NO(2), and NO(y) mixing ratios was conducted from Jul 28, 2008 to Sep 2, 2008 at the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP, CAS) station, which is 2km southwest to the Beijing National Stadium (Bird's Nest/Olympic Stadium). Photochemical pollution was detected during the measurement on Aug 2, 2008, and the maximum hourly average [O(3)] reached 128ppbv, caused by both the local photochemical reactions and regional transportation of pollutants. The NO(x) Ozone Production Efficiency (OPE (NO(x))) values were 6.9 and 20.2 on Aug 2 and Aug 24, 2008 respectively, which were the two days with highest O(3) pollution. The OPE (NO(x)) of 6.9 on Aug 2 was within a typical range in city area, and it implied that the high O(3) could be due to local sources. While OPE (NO(x)) of 20.2 on Aug 24 was larger than the typical value in the region, but lower than that of the surrounding clean area during 2008 Beijing Olympics Closing Ceremony. It indicated that the pollution was because of regional transportation of pollutants. In addition, 60% of the extent of the Smog Production Model (SPM) data was less than 0.6 and the rest was slightly larger than 0.6, with maximum of 0.78. It indicated that the sensitivity of O(3) generated was volatile organic compounds (VOCs) control during the observation period. The SPM results also implied that O(3) product in high-O(3) day is a transition state from VOCs sensitivity to NO(x) sensitivity. Lastly, the analysis of the wind direction and extent of SPM showed that the photochemical pollution of this region was mostly subject to the influence of southeastern air flow in the summer., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Based on the Beijing 325 m meteorological tower, O3, NOx and CO concentrations and meteorological parameters in urban atmospheric boundary layer were measured in July 2002. The variations of O3 concentration were remarkably different among the five levels. Contrasted with the higher levels, the daily variations were clear and the difference values between day and night were large in the lower levels. It was also found that the photochemistry reaction was an important source in boundary layer in daytime and precipitation process could arouse marked change of O3 concentration.

Rfn (formaldehyde/nitrogen dioxide) is a common indicator based on satellite observations used to classify ozone formation sensitivity. However, it may underestimate anthropogenic volatile organic compounds (VOCs) in heavily polluted cities when only formaldehyde (HCHO) is used in Rfn to measure VOCs, since it is mainly derived from natural sources worldwide. In this study, we used multiaxis differential optical absorption spectroscopy to acquire tropospheric observations of nitrogen dioxide (NO2), HCHO and glyoxal (CHOCHO) in Beijing from 1 April 2019 to 31 March 2020. Combined with VOCs detected simultaneously by gas chromatography—mass spectrometry and proton transfer reaction–time-of-flight/mass spectrometry near the ground, we evaluated the representativeness of HCHO column densities on total VOCs (TVOC) in equivalent propylene concentrations, which is called reactivity. The results showed that there were significant seasonal differences in the response of HCHO to TVOC reactivity, with fitting slopes of 2.3 (spring), 2.6 (summer), 2.9 (autumn) and 1.0 (winter) in the four seasons, respectively. Since CHOCHO can be used to partly characterize the contribution of anthropogenic VOC emissions and demonstrated a better response to TVOC reactivity in winter, with fitting slopes of 0.2 (spring), 0.2 (summer), 0.2 (autumn) and 0.5 (winter) in the four seasons, respectively, we introduced CHOCHO to construct a new indicator (HCHO + 6 × CHOCHO). The fitting slopes of the four seasons were more similar, being 3.2 (spring), 3.6 (summer), 4.0 (autumn) and 4.0 (winter). The ratio of the new indicator to NO2, Rmn ((HCHO + 6 × CHOCHO)/NO2), was used to reclassify the ozone formation sensitivity of urban areas in North China, revealing that it is a transition regime before 1300 LST (LST = UST + 8) and an NOx-limited regime afterwards. Rmn improved the sensitivity from the VOC-limited regime to the NOx-limited regime, enhancing the sensitivity of NOx and providing new robust support for ozone pollution prevention and control. [ABSTRACT FROM AUTHOR]

High loads of fine particulate matter (PM2.5) and ozone (O3) pollution occurred frequently since early spring and led to an increasing contribution of secondary organic aerosols (SOA) in organic aerosols. However, the characteristics of precursor volatile organic compounds (VOCs) have rarely been studied. In this study, the continuous observation of VOCs was performed by an offline VOC monitoring system and gas chromatography-mass/flame ionization detector from 1 April 2020 to 31 July 2020; the characterization of VOCs and their contribution to SOA was explored. The results showed that during the observation period, the average mixing ratio of TVOCs was 42.6 ± 11.2 ppbv, and the major VOCs species were OVOCs, followed by alkanes, halocarbons, aromatics, alkenes and acetylene. When the west circulation pattern functioned, the value of aromatics increased, and the relation between PM2.5, O3 and VOCs increased when the high-pressure system controlled by anticyclone functioned. In combination with the results of positive matrix factorization, the main emission sources of ambient VOCs were complex, and the fuel combustion, industry-related emission, vehicle emission, biogenic emission and solvent volatilization accounted for 27.1%, 24.4%, 24.3%, 12.1% and 12.0%, respectively. Moreover, the industry-related emission contributed the greatest to the generation of SOA. This result indicated that the restrictions on aromatics during the industrial process are vital to reducing SOA formation. [ABSTRACT FROM AUTHOR]

Smog chamber experimental systems, which have been widely used in laboratory simulation for studying atmospheric processes, are comprehensively reviewed in this paper. The components, development history, main research topics and main achievements of smog chambers are introduced. Typical smog chambers in the world, including their volumes, wall materials, light sources and features, are summarized and compared. Key factors of smog chambers and their influences on the simulation of the atmospheric environment are discussed, including wall loss, wall emission and background pollutants. The features of next-generation smog chambers and their application prospect in future studies of the atmospheric environment are also outlined in this paper. [ABSTRACT FROM AUTHOR]

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The characteristics of ozone variations and the impacts of synoptic and local meteorological factors in northern China were quantitatively analyzed during the warm season from 2013 to 2017 based on multi-city in situ ozone and meteorological data as well as meteorological reanalysis. The domain-averaged maximum daily 8 h running average O3 (MDA8 O3) concentration was 122±11 µ g m -3 , with an increase rate of 7.88 µ g m -3 yr -1 , and the three most polluted months were closely related to the variations in the synoptic circulation patterns, which occurred in June (149 µ g m -3), May (138 µ g m -3) and July (132 µ g m -3). A total of 26 weather types (merged into five weather categories) were objectively identified using the Lamb–Jenkinson method. The highly polluted weather categories included the S–W–N directions (geostrophic wind direction diverts from south to north), low-pressure-related weather types (LP) and cyclone type, which the study area controlled by a low-pressure center (C), and the corresponding domain-averaged MDA8 O3 concentrations were 122, 126 and 128 µ g m -3 , respectively. Based on the frequency and intensity changes of the synoptic circulation patterns, 39.2 % of the interannual increase in the domain-averaged O3 from 2013 to 2017 was attributed to synoptic changes, and the intensity of the synoptic circulation patterns was the dominant factor. Using synoptic classification and local meteorological factors, the segmented synoptic-regression approach was established to evaluate and forecast daily ozone variability on an urban scale. The results showed that this method is practical in most cities, and the dominant factors are the maximum temperature, southerly winds, relative humidity on the previous day and on the same day, and total cloud cover. Overall, 41 %–63 % of the day-to-day variability in the MDA8 O3 concentrations was due to local meteorological variations in most cities over northern China, except for two cities: QHD (Qinhuangdao) at 34 % and ZZ (Zhengzhou) at 20 %. Our quantitative exploration of the influence of both synoptic and local meteorological factors on interannual and day-to-day ozone variability will provide a scientific basis for evaluating emission reduction measures that have been implemented by the national and local governments to mitigate air pollution in northern China. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of O3, NO, NO2, and NOy mixing ratios were carried out at a station-Dinghushan in Guangdong province of China from Oct. 18th, 2008 to Nov. 7th, 2008. This research shows that under conditions of a strong subtropical high (temperature high, relative humidity low), on Oct. 29th, 2008 the Dinghushan station observed severe photochemical pollution. The Maximum hour average concentration of O3 reached 128 ppbv, and the serious photochemical pollution is caused by superposition of local photochemical reaction and regional transport. The observation that NO x ozone production efficiency (OPE) values for high O3 pollution on Oct. 29–30th, 2008 were 10.5 and 15, which were more than the values of the city source region and lower than that of the surrounding clean areas. It means the sensitivity of O3 generated was transitioning from VOCs limited condition to NOx-limited regime. By applying a Smog Production Model, the results show that the extent of reaction values less than 0.6 were occurred on 17 days during campaign, and 13 days for the extents of reactions more than 0.6. However, there were no data with values over 0.8, which indicates that the observation station represent a VOCs sensitive system during campaign. Analysis of the extents of reactions and wind data show that the pollution is mostly subject to a southeasterly airflow influence. [Copyright &y& Elsevier]

Ozone (O 3) pollution deteriorated in recent years in Beijing; however, the evolution characteristics and formation mechanism of O 3 pollution events (OPEs) lack comprehensive exploration from a long-term perspective. Based on 35-site (Beijing) and multi-city (North China) O 3 and meteorological monitoring and reanalysis data, totally 61 OPEs during 2013–2020 were counted in Beijing to reveal their characteristics, the relationship with regional pollution, and meteorological causes. Mild, moderate, and heavy pollution in all OPEs (203 ± 28 μg/m3 for averaged MDA8 O 3) accounted for 68.4%, 27.8%, and 3.8% of 291 days, respectively. 78.7% of OPEs were concentrated in May–July. The averaged MDA8 O 3 concentration, total days and durations of OPEs increased notably from 2013 to 2020, with a rate of 1.6 μg/m3/yr, 2.7 d/yr, and 0.2 d/yr, respectively. Overall, 90% (53%) of OPEs in Beijing co-occurred with regional pollution covering Beijing-Tianjin-Hebei (North China) under the predominant southerly airflow. Meteorological causes of different levels and spatial distribution of OPEs were explored through multi-scale weather processes. The increasing proportion of southwesterly-westerly synoptic circulation (49%–80%) and mountain-valley breeze (51%–70%), along with enhanced temperature, UV radiation, southerly wind, and temperature inversion and decreased relative humidity, collectively contributed to elevated levels of OPEs. The aforementioned meteorological condition facilitated O 3 photochemical reactions, the transport of pollutants, and hindered diffusion. Three spatial types (urban, northern and southern suburban pollution) of OPEs were determined by the intensity and direction of southerly wind. Additionally, daytime O 3 pollution elevated the mean peak O 3 of nocturnal O 3 enhancement events (NOEs) by 31 μg/m3 (41%) mainly induced by convective storms and low-level jets. Our comprehensive investigations of OPEs provide important scientific basis for the precise prediction and control of O 3 pollution in Beijing. [Display omitted] • OPEs in Beijing co-occur with regional pollution and elevated the peak of NOEs. • Southwesterly-westerly synoptic circulations and mountain-valley breeze enhanced OPEs. • Levels of OPEs increased with enhanced temperature and inversion, radiation, and southerly wind. [ABSTRACT FROM AUTHOR]

In recent decade, despite the implementation of strict emission reductions, PM 2.5 and surface ozone (O 3) in China are still at high pollution level. In this study, based on observations at air quality stations (∼1500 mainly in urban region), daily PM 2.5 and MDA8 (the daily maximum 8 h average) O 3 concentrations in high-density and uniform meteorological sites (∼2000) over China during 2017–2019 were retrieved using generalized additive models (GAMs) for different regions on a seasonal scale, in order to establish 0.1° gridded datasets and investigate their spatiotemporal characteristics, nonlinear effects of meteorology, and ambient air pollution-attributable health risks on a regional scale. This model can provide high accuracy in the estimation of daily PM 2.5 (O 3) in 2018 with overall cross-validation R2 and RMSE of 0.81 (0.80) and 12.73 (17.63) μg/m3 and predictive capability in 2017 and 2019 with R2 of 0.67 (0.70) for PM 2.5 (O 3). Temperature, relative humidity and visibility are three main meteorological factors driving PM 2.5 (O 3) response. PM 2.5 generally exhibits an exponential decrease with increasing visibility and an increase with increasing relative humidity, while is suppressed at the thresholds of 60% and 70%. For O 3 , in northern China, positive response of temperature is more important and O 3 suppression exists at 36 °C ∼ 41.5 °C, whereas negative response of relative humidity is dominating in southern China. Overall, annual averaged PM 2.5 (O 3) values across China reduced (increased) by 18.7% (11.2%) between 2017 and 2019, with the highest concentrations and variation in North China. These variations contributed to a 14.9% reduction in PM 2.5 attributed premature deaths, but a 10.4% increase in O 3 exposure related deaths. Generally, central-eastern China still exists greater health risk with per capita premature mortality ranging from 0.80‰ to 1.19‰ for PM 2.5 and 1.91‰ to 2.60‰ for O 3. Additionally, O 3 vegetation damages demonstrate a decline (increase) by 1.3% (21.7%) in North China with higher O 3 pollution (southern China with slight pollution) between 2017 and 2019. These findings highlight the essentiality for the synergistic control of PM 2.5 and O 3 based on regional differences in China. [Display omitted] • Daily PM 2.5 and O 3 at ∼2000 meteorological sites in China were constructed by GAM. • The PM 2.5 and O 3 models both shown a good performance and predictive capacity. • Northern China exhibits O 3 suppression, but more negative effect of humidity is in southern China. • PM 2.5 (O 3) levels and pollution- attributable premature deaths reduced (increased). • O 3 vegetation damages reduced (rose) in North (southern) China from 2017 to 2019. [ABSTRACT FROM AUTHOR]

Due to the complexity and nonlinearity of the ozone (O 3) production, it is vital to understand the detailed knowledge of ozone–precursor relationship for the formulation of effective mitigation of surface ozone pollution. In this study, continuous measurements of O 3 , volatile organic compounds (VOCs), and related parameters were conducted at an urban site of Beijing in the summer and autumn of 2019. The photochemical box model contained the Master Chemical Mechanism (MCMv3.3.1) was used to reveal the detailed information on the photochemical O 3 formation. Results show that the average concentration of total VOCs (TVOC) was 31.2 ± 10.7 ppb and 37.8 ± 18.9 ppb during the summer and autumn campaign, respectively, with the largest contribution from alkanes in both seasons, which mainly originated from liquefied petroleum gas (LPG) usage (20.2%–22.6%), gasoline vehicular exhaust (21.0%–21.6%), diesel vehicular exhaust (18.1%–18.3%), solvent usage (20.4%–24.1%), and fuel evaporation (16.4%–17.4%) that identified by positive matrix factorization (PMF) model. Heavy ozone pollution episodes were observed and the net local O 3 production rate during summer (EP1) and autumn (EP2) pollution episode was 9.87 ± 0.62 ppbv h−1, and 9.44 ± 1.18 ppbv h−1, respectively, which was both dominated by the reaction between HO 2 with NO. The analysis of relative incremental reactivity (RIR) and O 3 -NOx-VOC isopleth shows that ozone formation was VOC-limited in urban Beijing, with alkenes and aromatics contributed the most to O 3 formation in summer and autumn, respectively. In addition, modellings for various emission reduction scenarios were carried out, indicating the reduction of gasoline vehicles emissions in summer and both reduction of gasoline vehicles and solvent usage emissions in autumn is the best measures to efficiently reduce O 3 pollution. These results improved our understanding of O 3 precursors and their impact on ozone production and provided a more targeted reference for controlling ozone pollution in Beijing. [Display omitted] • Heavy ozone pollution episodes were observed in summer/autumn in urban Beijing. • O 3 production rate was camparable in summer and autumn that dominated by HO 2 -NO reaction. • O 3 formation in urban Beijing was VOC-limited and alkenes/aromatics contributed the most. • Traffic-related emissions were the major sources of VOCs during the observation period. • Various emission reduction scenarios were simulated and targeted reference was suggested. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) play a very important role in the formation of ozone and secondary organic aerosols. The concentrations, compositions, and variability of VOCs were measured from 2005 to 2008 at Dinghu Mountain Forest Ecosystem Research Station, a remote station in Southeast China. Weekly samples were collected in the Dinghu Mountain area and were analysed via gas chromatography–mass spectrometry. The results revealed that the total VOC concentrations decreased continuously and that the dominant VOC components were alkanes (43%) and aromatics (33%), followed by halo-hydrocarbons (12%) and alkenes (12%). The general trend of seasonal variation indicated higher concentrations in spring and lower concentrations in summer. The positive matrix factorization model was used to identify the sources of the VOCs. Seven sources were resolved by the PMF model: (1) vehicular emissions, which contributed 25% of the total VOC concentration; (2) industrial sources and regional transportation, contributing 17%; (3) paint solvent use, contributing 17%; (4) fuel evaporation, contributing 13%; (5) stationary combustion sources, contributing 12%; (6) biogenic emissions, contributing 10%; and aged VOCs, contributing only 6%. The HYSPLIT model was used to analyse the effect of pollutant transport, and the results indicated that the transport of pollutants from cities cannot be ignored. Finally, the OH radical loss rates and ozone formation potentials (OFPs) were calculated, and the results indicated isoprene to have the highest OH radical loss rate and toluene to be the largest contributor to the OFP at the Dinghu Mountain site. [ABSTRACT FROM AUTHOR]

With a decrease in fine particulate matter (PM 2.5) due to the implementation of air pollution prevention-control measures, ozone (O 3) has risen in China especially in urban areas recently. It becomes more and more important to control air combined pollution with high concentration of PM 2.5 and O 3. We analyzed the characteristics of air combined pollution in Beijing from 2014 to 2019 in this paper. Results indicated that the trough O 3 showed an upward trend of 4.5 μg m−3 yr−1, while the peak decreased by −1.1 μg m−3 yr−1. There were three typical atmospheric chemical stages in the interaction between O 3 and PM 2.5 in summer through observations. The first was an intense photochemical stage with the synchronous and rapid growth of O 3 and PM 2.5. The O 3 concentration varied from 68 μg m−3 to 206 μg m−3 when PM 2.5 ≤ 35 μg m−3. While secondary inorganic ions (SNA) ranged from 2 to 21 μg m−3 especially SO 4 2− (0.8–12 μg m−3). The second was an aerosol chemical generation stage with the rapid increase of PM 2.5 and SNA under high O 3 concentration. O 3 was maintained at a high concentration between 198 μg m−3 and 241 μg m−3 when PM 2.5 was within the range of 35–125 μg m−3. SNA increased from 12 μg m−3 to 96 μg m−3. The third was a high PM 2.5 pollution stage suppressing the generation of O 3 when PM 2.5 ≥ 125 μg m−3. O 3 began to decline with the growth of PM 2.5 and decreased from 224 μg m−3 to 130 μg m−3. Ultraviolet radiation (UV) decreased from 13 MJ m−3 in the first to 8 MJ m−3 in this stage. [Display omitted] • The O 3 trough increased by 4.5 μg/m3 and the peak decreased by −1.1 μg/m3 per year in Beijing. • There were three typical processes in the interaction between O 3 and PM 2.5 in summer day. • The photochemical process was intense in dry-sunny days with the synchronous growth of O 3 and PM 2.5. • Aerosol chemical process intensified with a rapid growth of PM 2.5 and SNA in high O 3. • O 3 began to decline with the growth of PM 2.5 when PM 2.5 attenuated UV in a high level. [ABSTRACT FROM AUTHOR]

Since NOx has decreased significantly, ozone formation sensitivity in urban areas has gradually shifted from VOC-limited to NOx-limited. Ozone is usually formed at high altitudes. However, due to a lack of vertical gradient observation data support, the evidence of high-altitude sensitivity change is still not conclusive. To confirm this issue, ozone and NOx were observed at three heights (8 m, 160 m, and 280 m) from a 325 m tower in Beijing from 2019 to 2020. Combined with the NO 2 and HCHO column concentrations, the ozone formation sensitivity transition was determined, and it was proposed that NOx control could effectively deal with high ozone concentrations. By comparing the observations from 2009 to 2010, near-surface NOx and ozone concentrations were found to have changed. A large decrease in NOx (−20 ppbv) and increase in ozone (19 ppbv) indicated that the weakening of the NO titration effect was the main cause of the increase. To remove the influence of the titration effect, the change in Ox (Ox = O 3 +NO 2) was analyzed and found to have increased by 6 ppbv. Local formation was not the main reason for Ox growth. After strict emission standards, the proportion of primary NO 2 and southward short-distance transport increased, which were two key reasons for the Ox increase. In addition, the boundary layer height increased by 208 m, and the surface relative humidity decreased by 6%. Meteorological conditions have become more conducive to ozone formation. This study shows that NOx emission reduction is conducive to controlling high-level ozone pollution. With the in-depth development of NOx emission reduction, the near-surface ozone will also significantly decrease. This study also highlights the importance of strict controls on diesel vehicles and motor vehicle numbers. • Meteorological conditions have become more favorable for ozone formation. • Primary NO 2 and southward short-distance transport increased. • Continuous NOx reduction can control ozone pollution. • VOCs should be controlled throughout the year, and NOx in summer. [ABSTRACT FROM AUTHOR]

Abstract: Regional composite pollution and variation of atmospheric oxidizing ability are significant problems in Beijing and its surrounding areas. In particular, a southwest–northeast prevailing wind makes nonlinear variation of ozone and its precursors complex. In this study, simultaneous measurements of surface ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), nitrogen oxide (NOx) and carbon monoxide (CO) were carried out from August 2009 to June 2010 to investigate ozone level and precursor concentrations in Northern China. Gucheng (GC), Longtanhu (LTH) and Xinglong (XL) were selected to represent rural area, urban area and background area in North China Plain, respectively. The results showed that there were two peaks for primary pollutants (NOx and CO) at urban and rural areas, and the highest values appeared nearly on rush hours. There was a single peak for O3 and Ox with peak values appearing at afternoon. The primary pollutants at urban and rural areas were higher than those in background region. However, the concentration of secondary pollutant O3 at downwind background areas was much higher than other sites due to transportation. Diurnal variations of pollutants indicated that O3 and Ox had peak values at afternoon, while other primary pollutants showed two peak values nearly on rush hours. Furthermore, high concentrations of O3 and Ox at background site XL also implied a robust atmospheric oxidizing ability. A positive correlation was observed between CO and O3 at XL site, which implied that air masses to the site had a large loading of anthropogenic emission experiencing strong photochemical processing. The correlation between CO and O3 was negative at GC and LTH, which indicated that local emission of precursors had significant influence on the formation of ozone. There was a positive correlation between NOx and Ox at GC and XL, which implied that NOx contributed to the formation of ozone, while a negative correlation meant titration in urban site LTH neutralized the formation of ozone due to high level of NO. [Copyright &y& Elsevier]

It's urgent to clarify the quantitative relationship between declining fine−particle (PM 2.5) concentrations and increasing ozone (O 3) levels as ozone pollution is increasingly severe in China. Here, we analyze the ground–based data of aerosol optical properties, particulates, and gaseous pollutants collected in a simultaneous observation in Kunming, locate in the Yunnan–Guizhou Plateau, from June 2014 to May 2017. The data exhibit slightly rising levels of PM 2.5 , O 3 , and carbon monoxid (CO), declining AOD (aerosol optical depth) but increasing AE (Angstrom exponent). Both the seasonal PM 2.5 and CO concentrations were low in the wet season and high in the dry season. The seasonal ozone levels and AE almost increased monotonically while the seasonal AOD decreased wavelike. Overall, the maximum daily 8 h average (MDA8) O 3 concentrations positively related to PM 2.5 concentrations with temperature>22 °C, RH<45%, and AOD<1.0 in the wet season. Generally, MDA8 O 3 concentrations didn't fluctuate with PM 2.5 concentrations in the dry season. High SSA (single scattering albedo) corresponded to high MDA8 O 3 concentrations and low SSA corresponded to low MDA8 O 3 concentrations in the wet season. However, lower SSA values in the dry season were observable. Most high MDA8 O 3 concentrations (>100 μg m−3) in the wet season occurred with AE at 1.0–1.5. High MDA8 O 3 concentrations (>100 μg m−3) in dry season appeared with an AE range of ~0.75–1.75. Low MDA8 O 3 concentrations occurred with AOD>2.0 and RH>75%, despite T>20 °C. The biomass−burning/urban aerosols were dominant (71.11% in the wet season and 74.40% in the dry season). The PSCF (Potential Source Contribution Function) results revealed the air pollutants from inside and outside China will have great impacts on the pollutant levels in Kunming besides the local emissions. Particularly, the severe pollution in India may aggravate Kunming's air pollution. • High SSA corresponded to high MDA8 O 3 concentrations and positive MDA8 O 3 − PM 2.5 relations were observable with SSA>0.95. • Most high MDA8 O 3 concentrations (>100 μg m−3) in the wet season occurred with AE at 1.0–1.5. • Biomass−burning/urban aerosols were dominant, accounting for over 70% of the whole aerosol types. • The air pollutants from outside China may have an important impact on the pollutant levels in Kunming. [ABSTRACT FROM AUTHOR]

With the increasingly severe ozone pollution in the Beijing-Tianjin-Hebei region in recent years, NO 2 photolysis has attracted our attention as the main source of tropospheric ozone generation. The photolysis rate of NO 2 (J(NO 2)) is of great importance for the quantification of photochemical ozone generation and photochemical pollution research, but its long-term changes in the Beijing-Tianjin-Hebei region remain unclear. An efficient reconstruction method for J(NO 2) was established via simulations with the troposphere ultraviolet and visible radiation (TUV) model and the observations of J(NO 2) and total ultraviolet (UV) radiation at a typical suburban site in the Beijing-Tianjin-Hebei region. We introduced the cloud modification factor in this method which improved the R2 value between the calculated and observed J(NO 2) values from 0.64 to 0.94 over the TUV clear-sky simulation level. A long-term (2005–2019) J(NO 2) dataset in Xianghe was reconstructed by applying this method. The annual mean J(NO 2) value reached 3.5*10−3 s−1 from2005 to 2019. The annual mean J(NO 2) value fluctuated slightly from 2005 to 2012 but increased evidently in the last 7 years. The increase rates of the annual mean J(NO 2) value and O(3P) generation via NO 2 photolysis were 1.3*10−4 s−1 per year and 1.1*10−3 ppb•s−1 per year, respectively, from 2013 to 2019. From 2005 to 2019, J(NO 2) exhibited the sharpest increasing trend in summer, but increased the least in spring. The monthly mean J(NO 2) value was the highest in May and the lowest in November. Our results demonstrated that to control the ozone concentration in the Beijing-Tianjin-Hebei region, we must pay more attention to the reduction in volatile organic compounds (VOCs) under the year-by-year increase in ambient J(NO 2). [Display omitted] • A flexible and accurate all-weather reconstruction method was established for JNO 2. • A long-term J(NO 2) dataset with high temporal resolution was reconstructed for the first time. • Increasing trends in J(NO 2) and O(3P) production were found during the period from 2013 to 2019. [ABSTRACT FROM AUTHOR]

Ozone concentrations have increased sharply since the implementation of the Clean Air Action plan in China, but the reasons for the increase are still unclear. Here, we analyzed the annual ozone trends at different altitudes from 2013 to 2018 based on ozonesonde observations in the southern suburb of Beijing. Large differences in ozone concentrations were observed among different years and were most significant within 2 km above the ground. Ozone in the lower boundary layer exhibited a strong increase before 2016 and a weak decrease after 2016, while ozone in the upper boundary layer exhibited a weak increase before 2016 and a strong decrease after 2016. The main factor responsible for these ozone trends was ozone precursors, which induced the transition of ozone production from being sensitive to VOC to being sensitive to NOx. This study indicated that a large amount of NOx reduction would be conducive to ozone pollution control in China. Unlabelled Image • The inter-annual variation of ozone is concentrated below 2 km above the ground. • Ozone precursors dominates the inter-annual change of ozone in Beijing. • Beijing has bypassed the NOx titration trap in ozone pollution control. • Continuous reduction of NOx would conducive to ozone pollution control in Beijing. [ABSTRACT FROM AUTHOR]