The EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation and their Effects in the Yangtze River Delta (EXPLORE-YRD) campaign was carried out between May and June 2018 at a regional site in Taizhou, China. The EXPLORE-YRD campaign helped construct a detailed air quality model to understand the formation of O3 and PM2.5 further, identify the key sources of elevated air pollution events, and design efficient emission control strategies to reduce O3 and PM2.5 pollution in YRD. In this study, we predicted the air quality during the EXPLORE-YRD campaign using the Weather Research and Forecasting/Community Multiscale Air Quality modelling system (WRF/CMAQ) and evaluated model performance on O3 and PM2.5 concentrations and compositions. Air quality was predicted using two sets of reanalysis data—NCEP Final (FNL) Operational Global Analysis and ECMWF Reanalysis v5.0 (ERA5)—and three horizontal resolutions of 36, 12, and 4 km. The results showed that PM2.5 concentration was generally under-predicted using both the FNL and ERA5 data. ERA5 yielded slightly higher PM2.5 predictions during the EXPLORE-YRD campaign. Both reanalysis data sets under-predicted the high PM2.5 pollution processes on 29–30 May 2018, indicating that reanalysis data is not essential for under-predicting extreme PM2.5 pollution processes. The performance of O3 was similar in both the reanalysis data sets, because O3 is mostly sensitive to temperature predictions and FNL and ERA5 yielded similar temperature results. Although the average performance of PM2.5 and O3 predictions yielded by FNL and ERA5 was similar, large differences were observed in certain locations on specific days (e.g. in Hangzhou between 29 May and June 6, 2018 and in Hefei on 1–3 June 2018). Therefore, the choice of reanalysis data could be an important factor affecting the predictions of PM2.5 and O3, depending on locations and episodes. Comparable results were obtained using predictions with different horizontal resolutions, indicating that grid resolution was not crucial for determining the model performance of both PM2.5 and O3 during the campaign. © 2020 Elsevier Ltd

To investigate the effects of biomass burning and photochemical oxidation on the black carbon (BC) mixing state and light absorption, a tandem centrifugal particle mass analyzer (CPMA) and single-particle soot photometer (SP2) system was used to measure ambient fine particulate BC during EXPLORE-YRD 2018 campaign (EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation, and their Effects in Yangtze River Delta). The mass ratio (MR) of the non-BC coating to BC core, a morphology-independent parameter to quantify the mixing state of BC-containing aerosols, is derived. Two types of periods were identified, namely non-significant biomass-burning period (NB), and enhanced biomass burning period (EB). The MR was higher during EB (2.3 ± 0.5), compared with during the NB (2.0 ± 0.5). MR showed bimodal diurnal variation with peaks in the early morning and early afternoon, mainly due to the biomass burning and photochemical processes, respectively. The light-absorbing enhancement ranged from 1.0 to 1.19 when MR was from 1.4 to 3.4. The relationship of rBC mixing state and its optical properties was parameterized, which can further be used in the regional model. © 2021 The Author(s)

In the present work, we propose a novel algorithm to determine the scattering coefficient of OA by evaluating the relationships of the MSEs for primary organic aerosol (POA) and secondary organic aerosol (SOA) with their mass concentrations at three distinct sites, i.e. an urban site, a rural site, and a background site in China. Our results showed that the MSEs for POA and SOA increased rapidly as a function of mass concentration in low mass loading. While the increasing rate declined after a threshold of mass loading of 50 μg/m3 for POA, and 15 μg/m3 for SOA, respectively. The dry scattering coefficients of submicron particles (PM1) were reconstructed based on the algorithm for POA and SOA scattering coefficient and further verified by using multi-site data. The calculated dry scattering coefficients using our reconstructing algorithm have good consistency with the measured ones, with the high correlation and small deviation in Shanghai (R2 = 0.98; deviations: 2.9%) and Dezhou (R2 = 0.90; deviations: 4.7%), indicating that our algorithms for OA and PM1 are applicable to predict the scattering coefficient of OA and Submicron particle (PM1) in China. © 2020 Elsevier Ltd

The EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation and their Effects in the Yangtze River Delta (EXPLORE-YRD) campaign was carried out between May and June 2018 at a regional site in Taizhou, China. The EXPLORE-YRD campaign helped construct a detailed air quality model to understand the formation of O3 and PM2.5 further, identify the key sources of elevated air pollution events, and design efficient emission control strategies to reduce O3 and PM2.5 pollution in YRD. In this study, we predicted the air quality during the EXPLORE-YRD campaign using the Weather Research and Forecasting/Community Multiscale Air Quality modelling system (WRF/CMAQ) and evaluated model performance on O3 and PM2.5 concentrations and compositions. Air quality was predicted using two sets of reanalysis data—NCEP Final (FNL) Operational Global Analysis and ECMWF Reanalysis v5.0 (ERA5)—and three horizontal resolutions of 36, 12, and 4 km. The results showed that PM2.5 concentration was generally under-predicted using both the FNL and ERA5 data. ERA5 yielded slightly higher PM2.5 predictions during the EXPLORE-YRD campaign. Both reanalysis data sets under-predicted the high PM2.5 pollution processes on 29–30 May 2018, indicating that reanalysis data is not essential for under-predicting extreme PM2.5 pollution processes. The performance of O3 was similar in both the reanalysis data sets, because O3 is mostly sensitive to temperature predictions and FNL and ERA5 yielded similar temperature results. Although the average performance of PM2.5 and O3 predictions yielded by FNL and ERA5 was similar, large differences were observed in certain locations on specific days (e.g. in Hangzhou between 29 May and June 6, 2018 and in Hefei on 1–3 June 2018). Therefore, the choice of reanalysis data could be an important factor affecting the predictions of PM2.5 and O3, depending on locations and episodes. Comparable results were obtained using predictions with different horizontal resolutions, indicating that grid resolution was not crucial for determining the model performance of both PM2.5 and O3 during the campaign. © 2020 Elsevier Ltd

Severe haze pollution occurs frequently in the winter over the Beijing-Tianjin-Hebei (BTH) region (China), exerting profound impacts on air quality, visibility, and human health. The Chinese Government has taken strict mitigation actions since 2013 and has achieved a significant reduction in the annual mean PM2.5 concentration over this region. However, the level of secondary aerosols during heavy haze episodes showed little decrease during this period. During heavy haze episodes, the concentrations of secondary aerosol components, including sulfate, nitrate and secondary organics, in aerosol particles increase sharply, acting as the main contributors to aerosol pollution. To achieve effective control of particle pollution in the BTH region, the precise and complete secondary aerosol formation mechanisms have been investigated, and advances have been made about the mechanisms of gas phase reaction, nucleation and heterogeneous reactions in forming secondary aerosols. This paper reviews the research progress in aerosol chemistry during haze pollution episodes in the BTH region, lays out the challenges in haze formation studies, and provides implications and directions for future research. [Figure not available: see fulltext.]. © 2020, Higher Education Press.

To investigate the regional secondary organic aerosol (SOA) formation at Yangtze River Delta (YRD) region, China, the chemical composition of fine particles and their gaseous precursors were simultaneously measured at a regional site, Taizhou, during EXPeriment on the eLucidation of the atmospheric Oxidation capacity, aerosol foRmation and their Effects in Yangtze River Delta (EXPLORE-YRD) intensive field campaign from May to June 2018. Secondary organic carbon (SOC) was estimated by both bottom-up and top-down method, i.e. the yield method from volatile organic compounds (VOCs) oxidation, and the elemental carbon (EC) tracer method. Our result showed that the oxidation of alkanes and aromatics measured by GC-MS/FID based on the yield method could only explain 25.3% of the SOC derived from the EC tracer method, in which aromatics were the dominant contributors (23.9%). This percentage increased to 39.5% while two semi-volatile organic compounds (SVOCs), i.e. naphthalene, and methylnaphthalene, were used in the calculation, suggesting the importance of SVOCs on SOA formation. The SOA formation pathways were further explored. The good correlation of SOC and odd oxygen (Ox) indicated the important role of photochemical reactions on SOA formation in the summer of YRD. Our findings evaluated the contributions of VOCs to SOA formation in Taizhou, revealed the importance of SVOCs to SOA formation and highlighted an urgent need for more exploration of SVOCs in the future. © 2020 The Authors

Organosulfates (OSs) are an important group of secondary organic aerosols, but the key influential factors of their formation in polluted atmospheres are not well understood. In this study, we monitored particulate OSs (carboxy OSs, hydroxyacetone sulfate, and isoprene-and monoterpene-derived OSs) at an urban site and a regional site in Beijing and examined their compositions and formation pathways under contrasting atmospheric conditions. The quantified OSs were most abundant in the summer at the regional site due to higher biogenic emissions and favorable formation conditions (higher aerosol acidity and humidity), followed by urban summer and winter conditions. Larger fractions of inorganic sulfate were converted to organosulfur when sulfate was less abundant. This implies that OSs would play more important roles in aerosol properties as the decline of sulfate. Monoterpene-derived nitrooxy-OSs were enhanced via NO3oxidation in the summer under high-NOxconditions at night, while the day-night variations in the winter were not as obvious. Among isoprene-OSs, IEPOX (isoprene epoxydiols)-OS formation was clearly suppressed under high-NOxconditions, while other isoprene-OSs that are favored under high-NOxconditions showed increasing formation with NOx. The results highlight that isoprene-OS formation pathways in polluted atmospheres could be different from the IEPOX-dominated regions reported for the low-NOxenvironments in the literature. © 2020 American Chemical Society. All rights reserved.

We present the analysis of the atmospheric budget of nitrophenols and nitrocresols, a class of nitroaromatics that raise great ecosystem and health concerns due to their phytotoxic and genotoxic properties, during the spring wheat harvest season in Eastern China. Significant quantities with maximum concentrations over 100 pptv and distinct diurnal patterns that peak around midnight and maintain low levels throughout the day were observed, in coincidence with the extensive open crop residue burning activities conducted in the vicinity. An observationally constrained zero‐dimension box model was constructed to assess the relative importance of various production and removal pathways at play in determining the measured surface concentrations. The NO3‐initiated dark chemistry, in concert with meteorological variations predominantly dilution and entrainment, exerts major controls over the observed diurnal behaviors of nitrophenols and nitrocresols. Structural isomerism is predicted to have a significant impact on the multiphase partitioning and chemistry of nitrophenol isomers. Furthermore, simulations show that an appreciable amount of nitrophenols is present in the aerosol water, thereby representing an important source of water‐soluble brown carbon in atmospheric aerosols under the humid subtropical weather prevailing during the campaign. Sensitivity analysis performed on the model parameterizations of reaction schemes helps to further understand the chemistry underlying the diurnal cycles. Implementing NO‐dependent yields of cresols from toluene photooxidation improves the model predictions of nitrocresols at low NO ranges (<1 ppb), thereby underscoring the complexity of the peroxy radical reaction pathways from toluene photooxidation under atmospheric relevant conditions.

氨是大气中广泛存在的碱性气体,已有的研究表明,氨能够参与包括硫酸/水体系的三元成核过程,进而促进新粒子的形成;同时,氨也是大气二次有机气溶胶（SOA）的重要前体物,对二次有机气溶胶的形成具有不可忽视的影响.了解大气中氨的污染情况,实现对大气中氨的高时间分辨率的在线观测,对于研究大气中氨的时空分布及来源解析,进而加深对气溶胶生成机理及气溶胶在大气辐射平衡与气候变化中作用的认识有重要意义.本研究使用一台自主搭建的质子转移反应质谱仪（PTR-MS）,以丙酮作为反应试剂,由电晕放电离子源产生质子化的丙酮反应试剂离子（（C3H6O）nH+）（n=1,2）,与大气中的气态氨及其他碱性气体发生质子转移反应后进行质谱检测.丙酮（C3H6O）相较于水（H2O）和乙醇（C2H5OH）,具有更高的质子亲和力(PA=194.1 kcal·mol-1),对PA较高的碱基化合物的选择性更好,可减少其他物质对四极杆质谱检测结果的影响.本研究在2017年11月9日—2018年1月10日和2018年11月12日—2019年1月2日华北地区气溶胶生成机理综合研究联合外场观测期间,将PTR-MS部署于山东省德州市平原县气象局观测场内,对大气中的氨气进行实时在线观测.结果表明,两次观测的气态氨平均值分别为（5.89±5.27） ppbv和（2.65±2.41） ppbv,均呈现出一个明显的日变化规律,即上午6:00—7:00出现峰值,随后逐渐下降,在下午大约15:00浓度达到最低值,随后上升.结合正交矩阵因子分解法（Positive Matrix Factorization, PMF）模型对当地近地面大气中氨气进行初步的来源分析,发现当地大气中氨气的来源主要是周边农村在冬季大量使用生物质燃料燃烧取暖造成的生活排放和当地交通源排放.两次冬季观测中当地农村取暖等生活排放分别占到66.0%和55.0%;交通排放在两次观测中分别占到27.0%和36.8%;农田土壤释放、畜牧养殖排放和工业排放等其他来源占比较低,分别是6.2%和7.5%;外部传输来源只占到很少一部分,分别是0.8%和0.7%.2018年的冬季观测相较于2017年,氨气浓度总体出现下降,主要来源还是以当地农村冬季生活和取暖燃烧排放为主,但通过相关政策管控,这一污染来源得到改善. 

挥发性有机物（VOCs）是臭氧和大气颗粒物的重要前体物，本研究利用在线气相色谱-质谱仪（Online-GC-MS）于2018年5—6月对江苏省泰州市大气中98种VOCs进行监测，依据监测结果对泰州市大气VOCs的组成特征、日变化趋势进行分析，对醛酮类VOCs数据进行参数化拟合探究其一次二次贡献，并采用正矩阵因子分解模型（PMF）对VOCs数据进行来源分析，用最大增量反应活性 （MIR）计算臭氧生成潜势 （OFP）。研究结果表明：泰州市大气VOCs中烷烃占比最高，其次为醛酮；烷烃、烯烃、卤代烃和芳香烃浓度日变化趋势明显，特征相近；参数化方法表明醛类物质主要来自于二次生成，而酮类物质主要来自一次排放；PMF模型结果表明泰州市VOCs的主要贡献源分别为机动车排放、油气溶剂挥发、生物质燃烧、其他工业和天然源；OFP的主要贡献物种为烯烃类，占比34.18%。研究结果表明，控制工业排放和溶剂使用是泰州市大气污染物控制的重点。

利用气相色谱-质谱仪/火焰离子检测器（Online-GC-MS/FID）对2017年冬季山东德州大气中99种挥发性有机物（VOCs）进行连续测量，研究了VOCs浓度和组分特征、日变化趋势、来源及其对臭氧(O3)、二次有机气溶胶（SOA）生成的贡献。结果表明，德州大气VOCs平均体积分数为（47.74±33.11）×10-9，烷烃占比最大，为40.66%。总VOCs及其组分表现出早晚体积分数高、中午体积分数低的日变化规律。德州大气中丙烷、丙烯、苯及甲苯和二氯甲烷分别受到液化石油气挥发、生物质燃烧、机动车排放和溶剂使用等人为源的影响。反向轨迹模型分析发现，北方内陆气团对德州VOCs体积分数具有一定贡献。烷烃、烯烃、芳香烃的臭氧生成潜势分别为（34.87±33.60）、（120.48±118.76）和（59.77±94.14）μg/m3，乙烯、丙烯、甲苯和间/对二甲苯的贡献较大。芳香烃氧化主导了SOA生成，其贡献率为93.7%，甲苯、间/对二甲苯、苯对SOA生成的贡献最大。为解决大气复合污染问题、实现臭氧和PM2.5协同控制，德州应重点控制甲苯、间/对二甲苯等芳香烃的排放。

Nitro-aromatic compounds (NACs) were measured hourly at a rural site in China during wintertime to monitor the changes due to local and regional impacts of biomass burning (BB). Concurrent and continuous measurements of the concentrations of 16 NACs in the gas and particle phases were performed with a time-of-flight chemical ionization mass spectrometer (CIMS) equipped with a Filter Inlet for Gas and Aerosol (FIGAERO) unit using iodide as the reagent ion. NACs accounted for < 2 % of the mass concentration of organic matter (OM) and total particulate matter (PM), but the total particle mass concentrations of these compounds can reach as high as 1000 ng m−3 (299 ng m−3ave.), suggesting that they may contribute significantly to the radiative forcing effects of atmospheric particles. Levels of gas-phase NACs were highest during the daytime (15:00–16:00 local time, L.T.), with a smaller night-time peak around 20:00 L.T. Box-model simulations showed that this occurred because the rate of NAC production from gas-phase sources exceeded the rate of loss, which occurred mainly via the OH reaction and to a lesser degree via photolysis. Data gathered during extended periods with high contributions from primary BB sources (resulting in 40–60 % increases in NAC concentrations) were used to characterize individual NACs with respect to gas-particle partitioning and the contributions of regional secondary processes (i.e. photochemical smog). On days without extensive BB, secondary formation was the dominant source of NACs and NAC levels correlated strongly with the ambient ozone concentration. Analyses of individual NACs in the regionally aged plumes sampled on these days allowed precursors such as phenol and catechol to be linked to their NAC derivatives (i.e. nitrophenol and nitrocatechol). Correlation analysis using the high time resolution data and box-model simulation results constrained the relationships between these compounds and demonstrated the contribution of secondary formation processes. Furthermore, 13 of 16 NACS were classified according to primary or secondary formation process. Primary emission was the dominant source (accounting for 60–70 % of the measured concentrations) of 5 of the 16 studied NACs, but secondary formation was also a significant source. Photochemical smog thus has important effects on brown carbon levels even during wintertime periods dominated by primary air pollution in rural China.