Nonmethane volatile organic compounds (NMVOCs) are important precursors of ozone (O3) formation under sufficient nitrogen oxide conditions. Understanding the characteristics and emission sources of NMVOCs, as well as the relationship between NMVOCs and O3, is of great significance for effective O3 pollution control. In this study, continuous online monitoring of NMVOCs was carried out in Zhengzhou, Henan, from 1–30 June. Furthermore, the study provided recommendations for strategies aimed at reducing O3 formation. During the observation period, the concentration of total NMVOCs (TNMVOCs) varied from 9.9 to 60.3 ppbv, with an average of 22.8 ± 8.3 ppbv. The average concentration of TNMVOCs during O3 pollution events was higher than on clean days. Six major sources of NMVOCs were identified using the positive-matrix-factorization model. Vehicular exhausts (28 %), solvent usage (27 %), and industrial production (22 %) were the main sources. We explore the O3–precursors relationship and propose observation-oriented O3 control strategies. The results of the relative incremental reactivity (RIR) and the Empirical Kinetics Modeling Approach show that Zhengzhou was under an anthropogenic volatile organic compound (AVOC)-limited regime. NMVOCs had the largest RIR value, while NOx exhibited a negative RIR value. It is noteworthy that the sensitivity of O3 formation to biogenic volatile organic compounds (BVOCs) was greater than that to AVOCs. Considering the reduction effect, it is recommended that the ratio of AVOCs to NOx be maintained at no less than 3:1 to effectively reduce O3 formation.

Carbonaceous aerosols (CA) have a profound impact on both the environment and climate, and in particular, secondary organic aerosols play multiple roles in different types of pollution events. In this study, high-resolution CA data were collected in four seasons in 2020 with organic carbon (OC) and elemental carbon (EC) components quantified by thermo-optical analysis at an urban site in the traffic-hub city of Zhengzhou, China. The concentration of ozone (O3) and fine particulate matter (PM2.5) were synchronously obtained by online analyzers. The characteristics and sources of CA on O3 and haze pollution days were analyzed in combination with hourly gaseous pollutants and meteorological data. OC and EC concentrations increased by 28 and 20 % on O3 pollution days compared to warm clean days and increased by 75 and 81 % on haze pollution days compared to cold clean days. The highest concentrations of secondary organic carbon (SOC) were observed in winter. SOC concentrations on O3 pollution days and haze pollution days were 1.4 and 1.7 times of corresponding clean days, respectively. Positive matrix factorization model results showed that CA was mainly from SOC (42 %), gasoline vehicles (27 %), and coal combustion (20 %). Compared with clean days, the contribution of coal combustion increased by 8 % on O3 pollution days, and the contribution of SOC increased by 5 % on haze pollution days, indicating that the primary and secondary pollution both significantly impact the air pollution in Zhengzhou city. SOC is more affected by local and surrounding areas during both O3 and haze pollution days. On O3 pollution days and haze pollution days, SOC has a positive correlation with O3 and relative humidity (RH), respectively, indicating that O3 and RH promote the generation of SOC.

Legacy and emerging PFAS in the air, wastewater, and sludge from two wastewater treatment plants (WWTPs) in Tianjin were investigated in this study. The semi-quantified nontarget PFAS accounted for up to 99 % of ƩPFAS in the gas phase, and aqueous film-forming foam (AFFF)-related PFAS were predominant in wastewater (up to 2250 ng/L, 79 % of ƩPFAS) and sludge (up to 4690 ng/g, 95 % of ƩPFAS). Furthermore, field-derived air particle-gas, air-wastewater, and wastewater particle-wastewater distribution coefficients of emerging PFAS are characterized, which have rarely been reported. The emerging substitute p-perfluorous nonenoxybenzenesulfonate (OBS) and AFFF-related cationic and zwitterionic PFAS show a stronger tendency to partition into particle phase in air and wastewater than perfluorooctane sulfonic acid (PFOS). The estimated total PFAS emissions from the effluent and sludge of WWTP A were 202 kg/y and 351 kg/y, respectively. While the target PFAS only accounted for 20-33 % of the total emissions, suggesting a significant underestimation of environmental releases of the nontarget PFAS and unknown perfluoroalkyl acid precursors through the wastewater and sludge disposal. Overall, this study highlights the importance of comprehensive monitoring and understanding the behavior of legacy and emerging PFAS in wastewater systems, and fills a critical gap in our understanding of PFAS exposure.

Organic acids in atmospheric particulate matter are widely involved in various physical and chemical reactions in the atmosphere and contribute greatly to the formation of secondary organic aerosols and haze pollutions. Therefore， the concentration distribution characteristics， sources， and secondary formation of organic acids in particulate matter are of great significance for further investigation of organic aerosols and their secondary transformation. Fine particulate matter （PM2.5） samples were collected in Zhengzhou， and three types of organic acids， including dicarboxylic acids， fatty acids， and resin acids， were analyzed to explore their species distribution， seasonal variations， source contribution， and secondary generation. Malonic acid （di-C3） and succinate acid （di-C4） were the most abundant in the identified dicarboxylic acids， which showed obvious seasonal variations in the order of summer > autumn > winter > spring. Fatty acids had the highest concentration in winter and the lowest concentration in spring， showing obvious bimodal advantages， with the most abundant compounds being palmitic acid and stearic acid （C18）. Principal component analysis and multiple linear regression （MLR） were used to analyze the source of organic acids in PM2.5 in Zhengzhou； the results showed that 35% of the organic acids came from combustion and traffic sources， 24% from cooking sources， 23% from secondary formation， and 17% from natural sources. The ratios of the selected marker species （i.e.， di-C3 / di-C4， F/M， and C18：1 / C18） were used as tracers for the secondary formation of the organic aerosol and its aging process. The results showed that the photochemical reaction was intense in summer， and the proportion of organic aerosol aging or secondary production was high， whereas the photochemical reaction was weak in winter， and the aging degree of organic aerosol was low. Correlation analysis and MLR were used in combination to quantify the relative contribution of gas-phase oxidation and liquid-phase oxidation to dicarboxylic acid formation， and the results showed that gas-phase oxidation played a dominant role in the sampling period （accounting for 58%）， especially in summer （61%）.

The chemical properties and secondary components of PM2.5 were investigated in the city of Zhengzhou, China. Water-soluble ionic species (Na+, NH4+, K+, Mg2+, Ca2+, F−, Cl−, NO3− and SO42−) contents, carbonaceous components (organic carbon (OC) and elemental carbon (EC)) in PM2.5 were measured for three years. The EC tracer method was used to estimate the secondary organic carbon (SOC) content, and the Interagency Monitoring of Protected Visual Environments formula was used to estimate light extinction due to the chemical composition of PM2.5. The annual mean concentrations of PM2.5 were 186, 180 and 218 µg m−3 in 2011, 2012 and 2013, respectively. These concentrations were 5–6 times greater than the National Ambient Air Quality Standards of China (annual value of 35 µg m−3) and indicated the presence of severe PM2.5 pollution in Zhengzhou. Particulate organic matter (OM) contributed the most (18–26

Against the backdrop of an uncertain evolution of carbonaceous aerosols in polluted areas over the long term amid air pollution control measures, this 11-year study (2011 -2021) investigated fine particulate matter (PM 2.5 ) and carbonaceous components in polluted central China. Organic carbon (OC) and elemental carbon (EC) averaged 16.5 and 3.4 mu g/m 3 , constituting 16 and 3 % of PM 2.5 mass. Carbonaceous aerosols dominated PM 2.5 (35 and 27 %) during periods of excellent and good air quality, while polluted days witnessed other components as dominants, with a significant decrease in primary organic aerosols and increased secondary pollution. From 2011 to 2021, OC and EC decreased by 53 and 76 %, displaying a high-value oscillation phase (2011 -2015) and a low-value fluctuation phase (post -2016). A substantial reduction in high OC and EC concentrations in 2016 marked a milestone in significant air quality improvement attributed to effective control measures, especially targeting OC and EC, evident from their decreased proportion in PM 2.5 . Primary OC (POC) in winter exhibited the most pronounced reduction (8 % per year), and the seasonal disparities in PM 2.5 and carbonaceous components were reduced, showcasing the effectiveness of control measures. Contrary to the more pronounced reduction of EC, which decreased in proportion to PM 2.5 , secondary OC (SOC) in PM 2.5 exhibited an increasing trend. Along with rising OC/EC, SOC/OC, and SOC/EC ratios, this indicates a growing prominence of secondary pollution compared to the decrease in primary pollution. SOC shows an increasing trend with NO 2 rise ( r = 0.53), without O 3 promoting SOC. Positive correlations of SOC with SO 2 , CO ( r = 0.41, 0.59), also highlight their influence on atmospheric conditions, oxidative capacity, and chemical reactions, indirectly impacting SOC formation. The implementation of precise precursor emission reduction measures holds the key to future efforts in mitigating SOC pollution and reducing PM 2.5 concentrations, thereby contributing to improved air quality.

Molecular analyses help to better understand the overall picture of characteristics, meteorological effects, sources, and secondary transformations of organic aerosols (OA). A two-year observation campaign was conducted in polluted central China during 2019-2021, and 130 compounds of molecular OA (quantified organic compounds, QOCs) were quantified. The average concentration of QOCs was 1971 ng/m(3), showing the highest normalized QOCs in PM2.5 (31 ng/mu g) compared to others. Among the QOCs, the polar category contributed 84%, with the dominated abundant fatty acids observed. The enhanced acid ratios of malonic/succinic and octadecanoic/oleic in summer indicated higher aerosol age, significantly promoted by temperature. Three benzenetricarboxylic acids, mostly from secondary formation, also exhibited quite high concentrations in summer. The noticeable presence of carcinogenic polycyclic aromatic hydrocarbons (PAHs) (45% of & sum;28PAHs) highlighted severe health risks associated with human exposure, particularly in winter (56 ng/m(3), approximately 7 times that in summer). According to the random forest model assessments, meteorological conditions in summer were most conducive to eliminating pollutants, while that in winter contributed 19% of QOC concentration. The Positive Matrix Factorization analysis revealed that anthropogenic secondary organic aerosols (ASOA) and biogenic SOA (BSOA) jointly accounted for 32% of QOCs, followed by biomass burning (20%), coal combustion (17%), vehicle emissions (16%), and cooking (15%). ASOA was positively correlated with O-3 (r = 0.58) and aerosol acidity facilitated ASOA production at 40% < relative humidity <80%. On polluted days, BSOA increased as NO2 and PM2.5 increased, contributing to worsened aerosol pollution. In spring and summer, gas-phase oxidation contributed more saturated dicarboxylic acids (52 and 55%), while aqueous-phase conversion predominated in autumn and winter (59 and 66%). This study provides new information on particulate molecular organic compounds as well as the secondary transformation, which is of great significance for formulating the prevention and control measures of aerosol pollution.

We conducted a simultaneous field study of PM2.5 -bound particulate polycyclic aromatic hydrocarbons (PAHs) and aromatic acids (AAs) in a polluted city Zhengzhou to explore the concentration, sources and potential conversion pathways between PAHs and AAs in different seasons. The average concentrations of PM2.5 , 28PAHs and 8AAs during the sampling period were 77 mu g/m3 , 75 ng/m3 , and 283 ng/m3 , respectively. The concentration of both 28PAHs and 8AAs were highest in winter and lowest in summer with ratios of 6.3 and 2.3, respectively. PAHs with 5-7 rings were the main components of PAHs (52%), followed by 4 rings PAHs (30%) and 2-3 rings PAHs (18%). According to the source appointment results obtained by positive matrix factorization, the main sources of PAHs were combustion and vehicle emissions, which account for 37% and 34%, respectively. 8AAs were divided into three groups, including four benzene dicarboxylic acids (B2CAs), three benzene tricarboxylic acids (B3CAs) and one benzene tetracarboxylic acid (B4CA). And interspecies correlation analysis with PM2.5 source markers were used to investigate potential sources. Phthalic acid ( o -Ph) was the most abundant specie of 8AAs (157 ng/m3 , 55% of 8AAs), which was well correlated with sulfate. Meanwhile, B3CAs and B4CA were highly correlated with sulfate and weakly correlated with levoglucosan, suggesting that secondary formation was their main source. As logical oxidation products of PAHs, o -Ph and B3CAs showed good correlations with a number of PAHs, indicating possible photochemical oxidation pathway by PAHs. In addition, O3 , NO2 , temperature and relative humidity have positive effects on the secondary formation of B3CAs. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Online volatile organic compounds (VOCs) were monitored before and after the Omicron policy change at an urban site in polluted Zhengzhou from 1 December 2022 to 31 January 2023. The characteristics and sources of VOCs were investigated. The daily mean concentrations of PM2.5 and total VOCs (TVOCs) ranged from 53.5 to 239.4 mu g m-3 and 15.6 to 57.1 ppbv, respectively, with mean values of 111.5 +/- 45.1 mu g m-3 and 36.1 +/- 21.0 ppbv, respectively, throughout the period. Two severe pollution events (designated as case 1 and case 2) were identified in accordance with the National Ambient Air Quality Standards (NAAQS) (China's National Ambient Air Quality Standards (NAAQS) from 2012). Case 1 (5 to 10 December PM2.5 daily mean = 142.5 mu g m-3) and case 2 (1 to 8 January PM2.5 daily mean = 181.5 mu g m-3) occurred during the infection period (when the policy of "full nucleic acid screening measures" was in effect) and the recovery period (after the policy was canceled), respectively. The PM2.5 and TVOC values for case 2 are, respectively, 1.3 and 1.8 times higher than those for case 1. The precise influence of disparate meteorological circumstances on the two pollution incidents is not addressed in this study. The results of the positive matrix factor modeling demonstrated that the primary source of VOCs during the observation period was industrial emissions, which constituted 32 % of the total VOCs, followed by vehicle emissions (27 %) and combustion (21 %). In case 1, industrial emissions constituted the primary source of VOCs, accounting for 32 % of the total VOCs. In contrast, in case 2, the contribution of vehicular emission sources increased to 33 % and became the primary source of VOCs. The secondary organic aerosol formation potential for case 1 and case 2 were found to be 37.6 and 65.6 mu g m-3, respectively. In case 1, the largest contribution of SOA formation potential (SOAP) from industrial sources accounted for the majority (63 %; 23.8 mu g m-3), followed by vehicular sources (18 %). After the end of the epidemic and the resumption of productive activities in the society, the difference in the proportion of secondary organic aerosol (SOA) generated from various sources decreased. Most of the SOAP came from solvent use and fuel evaporation sources, accounting for 32 % (20.9 mu g m-3) and 26 % (16.8 mu g m-3), respectively. On days with minimal pollution, industrial sources and solvent use remain the main contributors to SOA formation. Therefore, the regulation of emissions from industry, solvent-using industries, and motor vehicles needs to be prioritized to control the PM2.5 pollution problem.

Dust heterogeneous chemistry plays an important role in the atmosphere and has significant effects on climate and the environment. However, the traditional modelling method treats heterogeneous chemistry as pseudo-first-order reactions, which retains significant uncertainties, hindering the accurate prediction of secondary inorganic aerosols. In contrast, the actual dust heterogeneous chemistry involves complex multiphase reactions, including partition between gas- and dust-phase, and reactions on the dust surface. In this study, we implement a photocatalytic mechanism into the GEOS-Chem model and apply it to investigate the impact on atmospheric chemistry during a dust storm over East Asia during April 9–14th, 2018.With the photocatalytic heterogeneous chemistry (PHO), model simulation better reproduces observed sulfate and nitrate concentrations than those with the traditional pseudo-first-order mechanism (TDT) or without any dust heterogeneous chemistry at all (BASE). As validated against observations, normalized mean bias (NMB) in PHO reduces substantially compared to TDT, from −61.65% and 103.38% to −2.19% and 6.83% at Nanjing and Shanghai, respectively. The model also accurately simulates gaseous precursors such as SO2 and NO2, as evidenced by a decline in NMB from 103.38% to 81.80%–6.83% and 6.64% at the two sites, respectively. Furthermore, our analysis indicates that the larger dry deposition velocity of dust-phase sulfate and higher sulfate concentrations simulated by PHO jointly lead to a significant increase in SO4 dry deposition flux, demonstrating that the dust heterogeneous chemical process facilitates the removal of aerosol pollutants during dust events. These findings reinforce the need for enhancing the representation of dust heterogeneous chemistry in atmospheric models, underlining the criticality of this factor in accurate predictive modelling and environmental impact studies.

Electrochemical oxidation (EO) has been shown to have the unique ability to degrade perfluorooctanoic acid (PFOA), although the radical chemistry involved in this degradation is unclear, particularly in the presence of chloride ions (Cl-). In this study, reaction kinetics, free radical quenching, electron spin resonance, and radical probes were used to examine the roles of ·OH and reactive chlorine species (RCS, including Cl·, Cl2•-, and ClO·) in the EO of PFOA. Using EO in the presence of NaCl, PFOA degradation rates of 89.4%-94.9% and defluorination rates of 38.7%-44.1% were achieved after 480 min with PFOA concentrations ranging from 2.4 to 240 μM. The degradation occurred via the synergistic effect of ·OH and Cl· rather than through direct anodic oxidation. The degradation products and density functional theory (DFT) calculations revealed that Cl· triggered the first step of the reaction, thus the initial direct electron transfer was not the rate-limiting step of PFOA degradation. The change in Gibbs free energy of the reaction caused by Cl· was 65.57 kJ mol-1, which was more than two times lower than that triggered by ·OH. However, ·OH was involved in the subsequent degradation of PFOA. The synergistic effect of Cl· and ·OH in PFOA degradation is demonstrated for the first time in this study, which is promising for the development of electrochemical technology to remove perfluorinated alkyl substances from the environment.

Long-term trends in particulate-bound polycyclic aromatic hydrocarbon (PAH) concentrations in air in Zhengzhou (a severely polluted city in central China) between 2010 and 2018 were studied to assess the effectiveness of an air pollution prevention and control action plan (APPCAP) implemented in 2013. The PM2.5, sum of 16 PAHs (& sigma;16 PAHs), benzo[a]pyrene (BaP), and BaP toxic equivalent concentrations were high before 2013 but 41%, 77%, 77%, and 78% lower, respectively, after the APPCAP. The maximum daily & sigma;16 PAHs concentration between 2014 and 2018 was 338 ng/m3, 65% lower than the maximum of 961 ng/m3 between 2010 and 2013. The ratio between the & sigma;16 PAHs concentrations in winter and summer decreased over time and was 8.0 in 2011 and 1.5 in 2017. The most abundant PAH was benzo[b]fluoranthene, for which the 9-year mean concentration was 14 & PLUSMN; 21 ng/m3 (15% of the & sigma;16 PAHs concentration). The mean benzo[b]fluoranthene concentration decreased from 28 & PLUSMN; 27 ng/m3 before to 5 & PLUSMN; 4 ng/m3 after the APPCAP (an 83% decrease). The mean daily BaP concentrations were 0.1-62.8 ng/m3, and >56% exceeded the daily standard limit of 2.5 ng/m3 for air. The BaP concentration decreased from 10 & PLUSMN; 8 ng/m3 before to 2 & PLUSMN; 2 ng/m3 after the APPCAP (a 77% decrease). Diagnostic ratios and positive matrix factorization model results indicated that coal combustion and vehicle exhausts were important sources of PAHs throughout the study period, contributing >70% of the & sigma;16 PAHs concentrations. The APPCAP increased the relative contribution of vehicle exhausts from 29% to 35% but decreased the & sigma;16 PAHs concentration attributed to vehicle exhausts from 48 to 12 ng/m3. The PAH concen-tration attributed to vehicle exhausts decreased by 79% even though vehicle numbers strongly increased, indicating that pollution caused by vehicles was controlled well. The relative contribution of coal combustion remained stable but the PAH concentration attributed to coal combustion decreased from 68 ng/m3 before to 13 ng/m3 after the APPCAP. Vehicles made dominant contributions to the incremental lifetime cancer risk (ILCRs) before and after the APPCAP even though the APPCAP decreased the ILCRs by 78%. Coal combustion was the dominant source of PAHs but contributed only 12-15% of the ILCRs. The APPCAP decreased PAH emissions and changed the contributions of different sources of PAHs, and thus strongly affected the overall toxicity of PAHs to humans.

Wastewater treatment plants (WWTPs) are typical point sources of per- and polyfluoroalkyl substances (PFAS) released into the environment. The suspect and nontarget screening based on gas chromatography or liquid chromatography-high resolution mass spectrometry were performed on atmosphere, wastewater, and sludge samples collected from two WWTPs in Tianjin to discover emerging PFAS and their fate in this study. A total of 40 PFAS (14 neutral and 26 ionic) and 64 PFAS were identified in the atmosphere and wastewater/sludge, respectively, among which 5 short-chain perfluoroalkyl sulfonamide derivatives, 4 ionic PFAS, and 15 aqueous film-forming foam-related cationic or zwitterionic PFAS have rarely or never been reported in WWTPs in China. Active air sampling is more conducive to the enrichment of emerging PFAS, while passive sampling is inclined to leave out some ultrashort-chain PFAS or unstable transformation intermediates. Moreover, most precursors and intermediates could be enriched in the atmosphere at night, while the PFAS associated with aerosols with high water content or particles enter the atmosphere easily during the day. Although most emerging PFAS could not be eliminated efficiently in conventional treatment units, deep bed filtration and advanced oxidation processes could partly remove some emerging precursors.

Before and during the COVID-19 outbreak in the heated winter season of 2019, the carbonaceous fractions including organic carbon (OC), elemental carbon (EC), OC1-4, and EC1-5 were investigated between normal (November 1, 2019, to January 24, 2020) and lockdown (January 25, to February 29, 2020) periods in polluted regions of northern Henan Province. In comparison to urban site, four rural sites showed higher concentrations of carbonaceous components, especially secondary OC (SOC); the concentration of SOC in rural sites was 1.5-3.4 times that in the urban site. During the lockdown period, SOC in urban site decreased slightly, while it increased significantly in rural sites. NO2 has a significant effect on SOC generation, particularly in normal period when NO2 concentrations were high. Nevertheless, NO2 significantly decreased, and the elevated O3 (increased by 103-138%) contributed considerably to the generation of SOC during lockdown. Relative humidity (RH) promoted SOC production when RH was below 60%, but SOC was negatively correlated or uncorrelated with RH when RH exceeded 60%. Additionally, RH has a more pronounced effect on SOC during lockdown. The contribution of gasoline vehicle emissions decreases significantly in both urban and rural sites (3-12%) due to the significant reduction of anthropogenic activities during lockdown, although the urban site remained with the biggest contributions (37%). These results provide innovative insights into the variations in carbonaceous aerosols and SOC generation during the unique time when anthropogenic sources were significantly reduced and illustrate the differences in pollution characteristics and sources of carbonaceous fractions in different environments.

Abstract Wildfire emission inventories are usually applied with biome‐scale emission factors for atmospheric modeling. However, emission factors measured for different plant species vary substantially within the same biome. We apply the species‐specific emission factors and refine the Fire Emission Inventory‐northern Eurasia (FEI‐NE), and derive the wildfire black carbon emission inventory in northern Eurasia from 2002 to 2015. Our new inventory produces 61% more black carbon emissions than current estimates based on Global Fire Emission Database (GFED) and 33% less than FEI‐NE. Model simulations with different inventories are compared with ground‐based and satellite retrievals of aerosol absorption optical depth (AAOD). Compared with the Ozone Monitoring Instrument, the normalized root mean square deviation of AAOD over northern Eurasia is reduced from 1.0 under FEI‐NE to 0.95 through application of the new inventory. This study reveals the importance of applying sub‐biome‐scale emission factors for wildfire inventories development and revisiting emissions uncertainty in atmospheric modeling.

Peroxyacetyl nitrate (PAN) and ozone (O-3) are two typical indicators of photochemical pollution, which are harmful to human body and environment. In this study, PAN and O-3 were continuously monitored during static management (SM) of the COVID-19 epidemic in Zhengzhou. Briefly, SM refers to control policies in that all except for essential business are closed; work at home; and no people going out and no gathering, etc. During the SM, the temperature suddenly dropped from 26 degrees C to 14 degrees C, which provided a good experimental condition for the study of source transformation, accumulation, and consumption of PAN in the atmosphere. The concentrations of PAN were 0.6, 0.8, and 0.5 ppbv in three periods: before, during, and after the SM. During the SM, the lifetime of PAN was increased due to low temperature, and the accumulation time of PAN was longer, resulting in the increase of PAN concentration in daytime faster than the other two periods. During SM, especially after the temperature drops, the average atmospheric lifetime of PAN was 23.8 h, which was higher than 17.6 h before SM and 13.8 h after SM. This indicated that low temperature was more conducive to the accumulation of PAN. The high potential PAN source (CBPF>0.8) mainly came from the northeast of Zhengzhou, and the wind speed range was between 2.5 and 3 m/s. The backward trajectory analysis showed that 83.3% of the air mass from the northeast and northwest had a greater impact on the PAN concentration in Zhengzhou.

Polycyclic aromatic hydrocarbons (PAHs) have been extensively investigated in China. However, most previous studies only focused on specific locations. Here, we conducted field studies simultaneously to explore the seasonal characterization, sources, and source-specific risks of 16 PAHs in four polluted cities in China. Similar seasonal & sigma;16 PAHs variations are observed in all four sites with relatively high values in winter and low values in summer and the ratios of & sigma;16 PAHs between winter and summer range from 2.7 to 4.4. From summer to winter, the extent of PAH increase outpaces that of PM2.5 increase resulting in significant increase of n-ary sumation 16 PAHs/PM2.5 in winter. Five potential sources were resolved by PMF: (1) coal combustion (32-52%); (2) vehicle emissions (19-29%); (3) evaporation (9-26%); (4) coke oven emission (11-15%); and (5) biomass burning (5-13%). The highest fraction of evaporation is found in the Luoyang site due to the presence of many petrochemical plants, the largest oil refinery in Henan and large oil storage tanks. The coking factor contributes the largest proportion in Anyang site because of many out of date inefficient coking facilities. The source-related risks in four sites are all higher than the USEPA guideline value (1.0 x 10-6) except for biomass burning. The largest total risks are observed at Luoyang site, slightly higher than those of other cities. Our results suggest that the PAHs still need to be concerned due to the complexity of sources and source emitted risks in different type of cities, and specific source control strategies should be target in different regions.

In this study, 16 polycyclic aromatic hydrocarbons (PAHs) optimally controlled by the U.S. Environmental Protection Agency (EPA) were investigated. Three representative coal-fired power plants were selected as the research areas in Bijie, Guizhou Province, and 24 soil samples were collected totally from power plants at different depths and at different distances from the point pollution sources (plants). The physicochemical properties and microbial characteristics of the soil from the three power plants were also studied. The results showed that 16 PAHs were detected in all soils of the three power plants, with total concentrations ranging from 0.2 to 12.2 mg kg(-1), and that PAHs in the soils were mainly 2, 3 rings with percentages ranging from 42% to 82%. The proportions of low molecular weight (LMW) PAHs were higher near the contaminated plants. Moreover, since they were easily dispersed further away with atmospheric transfer, the proportions of lighter LMW PAHs were also higher far from the point source, while the proportions of heavier high molecular weight (HMW) PAHs were higher at some distance from the point source. In addition, the distribution patterns of PAHs in the soil at different depths were slightly different because the microbial activity in the surface soil at each sampling site was greater than that in the deeper soil, and the leaching behavior of each compound was different. Finally, based on the principal component analysis (PCA) method, coal combustion is not the only source of PAHs in soils from power plants, and vehicle emissions cannot be negligible.

Biomass burning emits large quantities of phenols, which readily partition into the atmospheric aqueous phase and subsequently may react to produce aqueous secondary organic aerosol (aqSOA). For the first time, we quantitatively explored the influence of phenols emitted from biomass burning on aqSOA formation in the winter of Beijing. A typical haze episode associated with significant aqSOA formation was captured. During this episode, aqueous-phase processing of biomass burning promoted aqSOA formation was identified. Furthermore, high-resolution mass spectrum analysis provided molecular-level evidence of the phenolic aqSOA tracers. Estimation of aqSOA formation rate (RaqSOA) with compiled laboratory kinetic data indicated that biomass-burning phenols can efficiently produce aqSOA at midday, with RaqSOA of 0.42 μg m-3 h-1 accounting for 15 % of total aqSOA formation rate. The results highlight that aqSOA formation of phenols contributes the haze pollution. This implies the importance of regional joint control of biomass burning to mitigate the heavy haze.

Biogenic secondary organic aerosol (BSOA) produced from naturally emitted biogenic volatile organic compounds (BVOCs) is closely affected by anthropogenic emissions. Reactive nitrogen oxides (NOx), sulfate (SO4), and primary organic aerosol (POA) modulate transformations of BVOCs by altering the oxidation pathways and gas-particle partitioning processes. China has experienced rapid changes in anthropogenic emissions recently, but the response of BSOA remains unclear. We conducted GEOS-Chem simulations to examine this response and found that isoprene-derived SOA increased (3.1%/yr) similarly as SO4 (3.6%/yr) over 2000-2006 but declined faster (-8.0%/yr) than SO4 (-4.3%/yr) over 2007-2015. Sensitivity simulations suggested that SO4 significantly promoted heterogeneous reactive uptake of isoprene epoxydiols (IEPOX) formed SOA (SOA(IE)), and a high level of NOx suppressed the production of IEPOX and subsequently reduced SOA(IE). The model roughly reproduced observed declines of secondary organic carbon (SOC) and SO4 at a rural site in South China over 2007-2011, although the mass concentrations were substantially underestimated. We find that BSOA would contribute slightly more to PM2.5 (2.8%) in 2050 under the RCP4.5 scenario than the present day (2.1%). This model-based work provides insights into historical and future changes of BSOA and implies the need to consider the controllable part for air quality management.