Search

The vast rural areas often experience more severe haze pollution than megacities during wintertime in North China Plain (NCP), yet the sources and evolution processes of aerosol particles, particularly organic aerosol (OA) remain poorly understood. Here we conducted real‐time measurements of submicron aerosol (PM1) species using a high‐resolution aerosol mass spectrometer at a representative rural site in NCP in winter 2019. Our results showed the dominance of organics (36%) and nitrate in PM1 (22%) in 2019. Positive matrix factorization analysis illustrated similarly important primary sources from traffic emissions, coal combustion, and biomass burning, yet secondary OA (SOA) from photochemical and aqueous‐phase related processing exceeded primary OA (53% vs. 47%). Substantial decreases in primary species and considerable increases in nitrate and sulphate were observed since winter 2018, demonstrating enhanced secondary formation in winter 2019. OA composition changed significantly from clean period to fog events with the contribution of aqueous phase‐related oxygenated OA increasing from 6% to 44%, while the photochemical SOA decreased correspondingly from 51% to 19%. The size distributions of aerosol species also changed by shifting toward large sizes during fog events. Elemental analysis of OA and the Van Krevelen diagram (H/C vs. O/C) illustrated the different roles of photochemical and aqueous‐phase processing during daytime and nighttime, respectively, and aqueous‐phase processing is subject to the formation of organic compounds with high H/C and O/C ratios. The large differences in fog processing of submicron aerosol species between 2018 and 2019 due to different temperatures were also elucidated. Plain Language Summary: Air quality in megacities in North China Plain (NCP) has been improved significantly during the last decade, however, severe haze pollution events occur frequently in vast rural areas during wintertime. Recent studies have demonstrated stronger health impacts of aerosol particles in rural area than megacities, yet the composition, sources and evolution processes of aerosol particles, particularly organic aerosol (OA) in rural area in NCP remain poorly characterized. Here we have a comprehensive characterization of submicron aerosol species at a rural site in winter in NCP. We observed substantial decreases in primary species and considerable increases in nitrate and sulphate from 2018 to 2019 due to enhanced secondary formation and the decreases in primary emissions. We found similarly important primary sources from traffic emissions, coal combustion, and biomass burning in rural area. However, secondary OA (SOA) from photochemical and aqueous‐phase related processing exceeded primary OA. The aqueous‐phase related SOA increased significantly by up to 44% during fog events, while the photochemical SOA decreased correspondingly from 51% to 19%. The size distributions, elemental composition of OA, and Van Krevelen diagram further illustrated the different roles of photochemical and aqueous‐phase processing in secondary aerosol formation in rural area in NCP. Key Points: Primary organic aerosol (OA) was primarily from coal combustion, biomass burning and traffic emissions in rural North China Plain in winterAqueous phase‐related OA showed large increases during fog events, while photochemical secondary OA was important during non‐fog periodsAerosol composition showed significant changes from 2018 to 2019 due to enhanced secondary formation and changes in primary emissions [ABSTRACT FROM AUTHOR]

Biomass burning and primary biological aerosol particles account for an important part of urban aerosols. Floods of studies have been conducted on the chemical compositions of fine aerosols (PM 2.5) in megacities where the haze pollution is one of the severe environmental issues in China. However, little is known about their size distributions in atmospheric aerosols in the urban boundary layer. Here, size-segregated aerosol samples were collected in Beijing during haze and clear days from April 2017 to January 2018. Three anhydrosugars, six primary saccharides and four sugar alcohols in these samples were identified and quantified by gas chromatography/mass spectrometry (GC/MS). Higher concentrations of a biomass burning tracer, levoglucosan, were detected in autumn and winter than in other seasons. Sucrose, glucose, fructose, mannitol and arabitol were more abundant in the bloom and glowing seasons. A particularly high level of trehalose was found in spring, which was largely associated with the Asian dust outflows. Anhydrosugars, xylose, maltose, inositol and erythritol are mainly present in the fine mode (<2.1 µ m), while the others showed the coarse-mode preference. The concentrations of measured tracers of biomass burning particles and primary biological particles in the haze events were higher than those in the non-hazy days, with enrichment factors of 2–10. Geometric mean diameters (GMDs) of molecular markers of biomass burning and primary biological aerosols showed that there was no significant difference in the coarse mode (>2.1 µ m) between the haze and non-haze samples, while a size shift towards large particles and large GMDs in the fine fraction (<2.1 µ m) was detected during the hazy days, which highlights that the stable meteorological conditions with high relative humidity in urban Beijing may favor the condensation of organics onto coarse particles.The contributions of reconstructed primary organic carbon (POC) by tracer-based methods from plant debris, fungal spores and biomass burning to aerosol OC in the total-mode particles were in the ranges of 0.09 %–0.30 % (on average 0.21 %), 0.13 %–1.0 % (0.38 %) and 1.2 %–7.5 % (4.5 %), respectively. This study demonstrates that the contribution of biomass burning was significant in Beijing throughout the whole year with the predominance in the fine mode, while the contributions of plant debris and fungal spores dominated in spring and summer in the coarse mode, especially in sizes >5.8 µ m. Our observations demonstrate that the sources, abundance and chemical composition of urban aerosol particles are strongly size dependent in Beijing, which is important to better understand the environmental and health effects of urban aerosols and should be considered in air quality and climate models. [ABSTRACT FROM AUTHOR]

A long-lasting high particulate matter (PM) concentration episode persisted over East Asia from May 24 to June 3, 2014. The Nested Air Quality Prediction Model System (NAQPMS) was used to investigate the mixing of dust and anthropogenic pollutants during this episode. Comparison of observations revealed that the NAQPMS successfully reproduced the time series PM 2.5 and PM 10 concentrations, as well as the nitrate and sulfate concentrations in fine (aerodynamic diameter ≤ 2.5 μm) and coarse mode (2.5 μm < aerodynamic diameter ≤ 10 μm). This episode originated from two dust events that occurred in the inland desert areas of Mongolia and China, and then the long-range transported dust and anthropogenic pollutants were trapped over the downwind region of East Asia for more than one week due to the blocked north Pacific subtropical high-pressure system over the east of Japan. The model results showed that mineral dust accounted for 53–83% of PM 10 , and 39–67% of PM 2.5 over five cities in East Asia during this episode. Sensitivity analysis indicated that the Qingdao and Seoul regions experienced dust and pollution twice, by direct transport from the dust source region and from dust detoured over the Shanghai area. The results of the NAQPMS model confirmed the importance of dust heterogeneous reactions (HRs) over East Asia. Simulated dust NO 3 − concentrations accounted for 75% and 84% of total NO 3 − in fine and coarse mode, respectively, in Fukuoka, Japan. The horizontal distribution of model results revealed that the ratio of dust NO 3 − /dust concentration increased from about 1% over the Chinese land mass to a maximum of 8% and 6% respectively in fine and coarse mode over the ocean to the southeast of Japan, indicating that dust NO 3 − was mainly formed over the Yellow Sea and the East China Sea before reaching Japan. [ABSTRACT FROM AUTHOR]

The impact of heterogeneous reactions on the chemical components and mixing state of dust particles are investigated by observations and an air quality model over northern China between March 27, 2015 and April 2, 2015. Synergetic observations were conducted using a polarization optical particle counter (POPC), a depolarized two-wavelength Lidar and filter samples in Beijing. During this period, dust plume passed through Beijing on March 28, and flew back on March 29 because of synoptic weather changes. Mineral dust mixed with anthropogenic pollutants was simulated using the Nested Air Quality Prediction Modeling System (NAQPMS) to examine the role of heterogeneous processes on the dust. A comparison of observations shows that the NAQPMS successfully reproduces the time series of the vertical profile, particulate matter concentration, and chemical components of fine mode (diameter ≤ 2.5 μm) and coarse mode (2.5 μm < diameter ≤ 10 μm) particles. After considering the heterogeneous reactions, the simulated nitrate, ammonium, and sulfate are in better agreement with the observed values during this period. The modeling results with observations show that heterogeneous reactions are the major mechanisms producing nitrate reaching 19 μg/m 3 , and sulfate reaching 7 μg/m 3 , on coarse mode dust particles, which were almost 100% of the coarse mode nitrate and sulfate. The heterogeneous reactions are also important for fine mode secondary aerosols, for producing 17% of nitrate and 11% of sulfate on fine mode dust particles, with maximum mass concentrations of 6 μg/m 3 and 4 μg/m 3 . In contrast, due to uptake of acid gases (e.g. HNO 3 and SO 2 ) by dust particles, the fine mode anthropogenic ammonium nitrate and ammonium sulfate decreased. As a result, the total fine mode nitrate decreased with a maximum of 14 μg/m 3 , while the total fine mode sulfate increased with a maximum of 2 μg/m 3 . Because of heterogeneous reactions, 15% of fine mode secondary inorganic aerosols and the entire coarse mode nitrate and sulfate were internally mixed with dust particles. The significant alterations of the chemical composition and mixing state of particles due to heterogeneous reactions are important for the direct and indirect climate effects of dust and anthropogenic aerosols. [ABSTRACT FROM AUTHOR]

Benefiting from the pollution controls implemented by the Chinese government, the concentrations of PM 2.5 , SO 2 , NO 2 and CO showed a significant decrease in Beijing during 2013–2017. In this study, an observation-based method was employed to estimate the relative contributions of regional transport (MaxRTC) and local emissions (MinLEC) to air pollutant levels during 2013–2017 in Beijing. The results showed that the MaxRTC to SO 2 and PM 2.5 increased significantly over the five years, while those to CO and NO 2 changed little. Furthermore, the difference in the emissions control efficiency (ΔECE) between Beijing (receptor region) and Shijiazhuang (source region), which refers to the concentration changes corresponding to unit emission changes of a certain air pollutant between the two regions, was introduced to verify the estimated variation in MaxRTC and MinLEC over 2013–2017. The negative value of Δ ECE found for PM 2.5 and SO 2 supports the conclusion of an increasing effect of regional transport. This implies that local emissions control alone is not adequate for mitigating Beijing's air pollution, especially with the demand for continuously improving air quality. Joint prevention and control with regard to air quality on a regional scale is more important and urgent in the next Five-Year Plan. [Display omitted] • Regional transport to SO 2 and PM 2.5 in Beijing increased during 2013–2017. • Contributions of local emission to NO 2 in Beijing are still important. • Emissions control efficiency is useful to verify the trend of regional transport. • Joint prevention and control on air quality is important in next Five-Year Plan. [ABSTRACT FROM AUTHOR]

Secondary inorganic aerosol (SIA) is the key driving factor of fine-particle explosive growth (FPEG) events, which are frequently observed in North China Plain. However, the SIA simulations remain highly uncertain over East Asia. To further investigate this issue, SIA modeling over North China Plain with the 15 km resolution Nested Air Quality Prediction Model System (NAQPMS) was performed from October 2017 to March 2018. Surface observations of SIA at 28 sites were obtained to evaluate the model, which confirmed the biases in the SIA modeling. To identify the source of these biases and reduce them, uncertainty analysis was performed by evaluating the heterogeneous chemical reactions in the model and conducting sensitivity tests on the different reactions. The results suggest that the omission of the SO2 heterogeneous chemical reaction involving anthropogenic aerosols in the model is probably the key reason for the systematic underestimation of sulfate during the winter season. The uptake coefficient of the "renoxification" reaction is a key source of uncertainty in nitrate simulations, and it is likely to be overestimated by the NAQPMS. Consideration of the SO2 heterogeneous reaction involving anthropogenic aerosols and optimization of the uptake coefficient of the "renoxification" reaction in the model suitably reproduced the temporal and spatial variations in sulfate, nitrate and ammonium over North China Plain. The biases in the simulations of sulfate, nitrate, ammonium, and particulate matter smaller than 2.5 μm (PM2.5) were reduced by 84.2%, 54.8%, 81.8%, and 80.9%, respectively. The results of this study provide a reference for the reduction in the model bias of SIA and PM2.5 and improvement of the simulation of heterogeneous chemical processes. [ABSTRACT FROM AUTHOR]

Dust aerosol has important climate and environmental effects, which could be changed by internally mixing with anthropogenic aerosol as a result of heterogeneous reactions; however, the importance of these reactions is not fully understood yet. In this study, synergetic observations and an air quality model were used to analyze the transport of a severe dust storm and its impacts on nitrate and sulfate levels over East Asia between 3 and 11 May 2017. The model successfully reproduced the occurrence and transport of the dust storm compared to dust RGB imageries of the Himawari-8 satellite and dust extinction coefficients observed by LIDAR. The model also reasonably simulated the variations of observed nitrate and sulfate concentrations, and the results indicated that the dust heterogeneous reactions were dominant pathways for nitrate formation, but they had limited contribution for sulfate in both fine and coarse mode in Fukuoka, Japan. Dust nitrate formed rapidly after leaving China, and the highest period-averaged concentration of dust nitrate (>5 μg m−3) was shown over the Yellow Sea. Based on model results; we found that the mass ratio of dust nitrate to dust aerosol could reach 10% over the Pacific Ocean. Our results confirmed the importance of heterogeneous reactions on compositions of dust particles. [ABSTRACT FROM AUTHOR]

East Asia is suffering from both severe air pollution problem due to intensive anthropogenicemissions and natural mineral dust aerosols. During transport, the aerosol particles undergocomplex mixing processes, resulting in great impacts on regional air quality, human healthand climate. In this study, we conducted a long-term observation using an Optical ParticleCounter equipped with a Polarization detection module (POPC) at an urban sitein Beijing. Mass concentrations of both PM2.5 and PM10 estimated from POPCcompared well with ground-based measurements. The results revealed that theobserved depolarization ratio (DR, termed as the ratio of the intensity of the s-polarizedsignal to the intensity of the 120 degree backward scattering signal [s/(s + p)])for aerosol particles in the fine mode was generally much lower in summer thanthat in spring as a result of predominance of different aerosol types. Mineral dustparticles in the coarse mode normally had a large DR value (0.3 ± 0.05) owing to theirnon-spherical shape; however, particles in the fine mode consisted of large proportionwater-soluble compositions, which lead to apparent decrease of their DR values inparticular high relative humidity (RH) condition. Because the observation site wassubject to frequent impact of dust event in spring, DR value of particle at 1 μm wasalmost twice as high as that (0.07 ± 0.01) in summer. Based on size-resolved DRvalues, anthropogenic pollutants, mineral dust and polluted mineral dust particles,and their contribution to local air quality were well distinguished. About 26.7%of substandard days (daily averaged PM2.5 concentration larger than 75 μg/m3)in Beijing was featured by high atmospheric loading of coarse-mode particles inwinter-spring time. In particular during severe pollution episode in winter, the DRvalues of coarse mode particles decreased by 13%, implies the high possibility ofdust-related heterogeneous processes on pollution formation. During dust event, DRvalues of particle at Dp = 5 μm decreased evidently with increase of PM2.5/PM10ratio as well as RH, indicating of the morphological changes of mineral dust. Thisstudy confirmed that high RH tends to promote water absorption processes on thedust surface as well as coating of soluble compounds, and suggested that complexmixing of dust and anthropogenic particles may lead to underestimate impact ofdust particles in urban area based on remote sensing technique, and interactionbetween dust particle and pollutants should be well considered by the optical model. [ABSTRACT FROM AUTHOR]

Scientifically and efficiently ensuring good air quality for important events is an issue of concern to the government. In addition to analysis based on historical data, advanced prediction before an event is essential for the government having ample time to take effective actions to improve air quality during the event period. Taking "the 2022 Olympic Winter Games (OWG)" as a typical case, a chemical transport model coupled with a tracer-tagged module was used to evaluate the air quality and source apportionment of ambient pollutants in the OWG host cities under historical and predicted meteorological conditions. Driven by the downscaling of meteorological fields from an operational real-time climate forecast system, the potential ability of air quality forecasting three months ahead was investigated, which was meaningful for designing control strategies. Sensitive simulations indicated that under unfavorable meteorological conditions, such as those during February 2014, both Beijing and Zhangjiakou faced a high risk of experiencing haze episodes, even based on current anthropogenic emission intensity. The contribution of the joint prevention and control region to Beijing and Zhangjiakou would become larger under worse meteorological conditions, which favor heavy air pollution. The source apportionment results indicated that strengthened emission control in cities including Beijing, Zhangjiakou and south of Beijing (Baoding, Langfang, Tianjin, and Tangshan) is effective for reducing haze episodes in the host cities. There is still a long way to make accurate daily fine particulate matter predictions on a seasonal-scale in advance; however, it could capture the trends in air quality in host cities around the OWG period three months ahead. The comparison of observations and predictions confirmed and highlighted the role of regional emission controls on the realization of the "OWG blue". • Regional transport became larger under conditions favoring heavy air pollution. • The trend of air quality was captured by seasonal-scale model forecasting. • Joint emission control measures ensured the realization of the "OWG blue". [ABSTRACT FROM AUTHOR]

The uncertainty in the quantitative estimates of long-range transport of pollutants in air quality models is large. In this study, based on the Global Nested Air Quality Prediction Modeling System (GNAQPMS-SM), using Latin hypercube sampling (LHS) method, we conducted a base simulation and an ensemble of 1° × 1° simulations in April 2017 to assess the uncertainty in model estimates of O 3 and PM 2.5 intercontinental transport from uncertainties in input parameters (emissions, temperature, wind field). The results show that the base simulation has biases in some regions, and when the uncertainty of input parameters is taken into account, the observations mostly lie within the uncertainty range of the 50 simulated group samples. The uncertainties of input parameters are reasonably quantified in terms of their propagation during computation in GNAQPMS-SM. The best performance occurs with the multiple linear regression (MLR) method, which is used to fit ensemble simulation results. The uncertainty range of monthly O 3 transport from North America (NAM) to Europe (EUR) at a 1.2 km altitude is 4.91–5.44 ppb, from EUR to China is 0.78–0.96 ppb, and from China to NAM is 0.76–0.85 ppb. Correspondingly, the MLR result of each is 5.12 ppb, 0.80 ppb, and 0.77 ppb, respectively. The MLR result is thought to be closer to the actual transport amounts, and most of them lie within the uncertainty range. The appreciable differences between base simulation and MLR results reflect the uncertainties in the input parameters. Finally, taking O 3 transport from China to Japan as an example, the maximum absolute value of the daily average Spearman correlation coefficient | ρ ‾ | max between input parameters and contributions is calculated to identify the key uncertainty sources in several regions of O 3 transport to Japan. Meteorological and air pollutant observations and the performance of meteorological simulations should be strengthened. [Display omitted] • An uncertainty analysis is conducted to estimate uncertainties of S-R relationships. • The uncertainties of input parameters well explain most of the simulation deviation. • The uncertainties of S-R relationships are reasonably quantified. • Key uncertainty source during O 3 transport from East China to Japan is identified. • Meteorological and air pollutant monitoring are suggested to be strengthened. [ABSTRACT FROM AUTHOR]

Air quality in Beijing-Tianjin-Hebei and its surrounding regions has been significantly improved during the Three-Year Action Plan for Winning the Battle Against Air Pollution from 2018 to 2020. The PM 2.5 concentration can be significantly influenced by meteorological conditions, and the effectiveness of anthropogenic emissions reduction on PM 2.5 over the North China Plain remains unclear. In this study, the Nested Air Quality Model System (NAQPMS) and observations were used to quantitatively examine the contribution of meteorological and emission variations to autumn-winter (November to February) PM 2.5 concentrations in Beijing and its surrounding regions from 2018 to 2020. The model reproduced the temporal evolution of atmospheric pollutants and components well. The results showed that the observed mean PM 2.5 concentrations during the winter were reduced by 15% and 29% in 2019 and 2020, respectively, compared with that in 2018. In 2019, the meteorological conditions over the Beijing-Tianjin-Hebei (BTH) region were poor, causing an increase of PM 2.5 by 7.6% in BTH and 11% in Beijing; therefore, the control of air pollutant emission compensated for the unfavorable influence of meteorology and emission reduction was the decisive factor for PM 2.5 reduction; In 2020, the meteorological conditions were relatively favorable, and the changes in meteorological factors and emission reduction led to a decrease in PM 2.5 concentration by 18.6% and 10.5%, respectively, compared to 2018. Emission reduction also contributed to decrease in nitrate, ammonium, organic matter, element carbon and precursors. This work confirmed the obvious environmental benefit of pollution control measures from 2018 to 2020. There was obvious regional heterogeneity in the effect of meteorology and the impact of adverse meteorological conditions should be considered during the formulation of air pollution control measures. The results can serve as a reference for the formulation of air quality objectives or the evaluation of the environmental effect of pollution control schemes. • The effect of winter meteorology and control measures in 2018 to 2020 was assessed. • Observed winter PM 2.5 reduced by 15% and 29% in 2019 and 2020, respectively, compared to 2018. • Unfavorable meteorology in 2019 partially counteracted the emission control effects. • Emission mitigation played an important role in air quality improvement. [ABSTRACT FROM AUTHOR]

With continuous strengthening of emission control actions, the air quality in northern China during winter has been improved in recent years. However, the fine particulate matter (PM 2.5) concentration remains high in the Central Plains Economic Region (CPER). The Nested Air Quality Prediction Modeling System coupled with an on-line source-tagged model was applied to investigate the source apportionment of primary and secondary PM 2.5 in the most polluted area of China from November 2017 to March 2018. On average, local emissions represent the largest contributor to ambient PM 2.5 levels, followed by transport from circumjacent cities at five receptors in northern CPER. Under high PM 2.5 concentrations (more than 150 μg/m3), 60%–70% of the primary PM 2.5 is freshly emitted on the current day, while the contribution of the current day, one day ago, and two or more days ago are comparable to secondary aerosols. The estimation of contributions based on distance shows that the contribution from regions within 200 km reaches more than 80% of the primary PM 2.5 , while the contribution from long-range transport within 200–500 km still accounts for more than 20% of the secondary PM 2.5 at the receptor sites. These results indicate that control measures of primary particle emission should be effective to reduce the primary PM 2.5 levels within local and nearby regions, and control measures of gas phase precursors one or more days in advance should be beneficial to surrounding regions within 500 km. The process analysis results of the change in PM 2.5 mass over the northern part of the CPER during increased PM 2.5 periods illustrate that the existing particle total transport is smaller than the secondary aerosol chemical production and primary aerosol emissions since the westerly and southerly net inputs are mostly offset by the large net outputs at the east boundary in both cases. This finding indicates that the ambient PM 2.5 mass in a selected area is strongly affected by the upstream region; meanwhile, the PM 2.5 in this area also spreads to the downstream region. Joint prevention and control measures that cooperate with upstream regions for both primary particles and gas phase precursor emissions are crucial for improving the air quality over polluted areas. As the emission control measures would lead to some economic losses, beneficiary downstream regions could reasonably provide certain economic compensation to upstream regions if emergency control measures are taken. • Reduce the primary PM 2.5 emission is benefit to local and nearby regions. • Joint control measures of gas phase precursors should be taken in advance. • Control measures need to be taken in upstream regions during haze episodes. [ABSTRACT FROM AUTHOR]