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. 

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。

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。

In this study, the black carbon (BC) measurements in the atmosphere of Nanjing, China were continuously conducted from 2015 to 2018 using a Model AE-33 aethalometer. By combining dataset of PM2.5, PM10, CO, NO2, SO2, O3 and meteorological parameters, the temporal variations and the source apportionment of BC were given in this study. The results showed that the PM2.5 mass concentrations decreased in Nanjing, with an average annual rate of variation of 6.50 μg/(m3⋅year). Differently, the annual average concentrations of BC increased with an average annual variation rate of 214.71 ng/(m3⋅year). The seasonal variations showed the pattern of BC mass concentrations in winter > autumn > spring > summer. The diurnal variations of BC mass concentrations showed a double-peak in all four seasons. The first peak occurred at approximately 7:00 in spring, summer and autumn and around 8:00 in winter. The second peak took place after 18:00. The average AAE (absorption Ångström exponent) was 1.26 with a maximum of 1.35 during wintertime and the lowest (1.12) during summertime. In addition, the AAE was smaller in the daytime than that at night, with a minimum occurring between 13:00 and 14:00. BC and visibility show a good power-function relationship at different humidity levels. The average values of the visibility thresholds of the BC mass concentrations in spring, summer, autumn and winter were 1.326, 5.522, 1.340 and 0.708 μg/m3, respectively. The greater the relative humidity, the smaller the visibility threshold for the BC mass concentrations was. © 2020

Most previous studies treat regional transport of aerosols as a whole, without distinguishing the transport of secondary aerosols and that of their precursors. A new method of quantifying the transport forms of secondary inorganic aerosols (SIA) using the Nested Air Quality Prediction Modeling System was proposed. The contribution of nonlocal emissions to SIA in the receptor region was divided into three parts: (1) SIA chemically formed by nonlocal emissions in their source regions; (2) SIA chemically formed by nonlocal emissions during transport; and (3) SIA chemically formed by nonlocal emissions in the receptor region, representing transport of precursors. In the North China Plain, the transport of precursors and SIA produced during transport are the two main transport forms. Furthermore, the contribution from transport of precursors increased under polluted conditions in most cities. The results indicate that joint control of precursors is paramount for mitigating air pollution. ©2020. The Authors.

Spectral light-absorption properties measured with an Aethalometer (AE; Model AE33; Magee Scientific) are widely used in radiative forcing studies and source appointment in China. However, considerable uncertainty regarding the measured absorption coefficient (σabs) exists because of the multiple-scattering effects, loading effects, and differences in filter tape. This study evaluated σabs by comparing the values measured with an AE33 using Tape 8050, an AE33 using Tape 8060 (which differs from Tape 8050 in material), and a three-wavelength photoacoustic soot spectrometer (PASS-3) during two field campaigns in eastern China. The results indicated that the AE33-measured σabs using either tape exceeded the PASS-3-measured value by approximately three times, mainly owing to the multiple-scattering effect. A wavelength-independent multiple-scattering compensation factor (2.90), which varies slightly (± 0.04) for eastern China, is recommended for these regions. When σabs was measured with the AE33 using Tape 8050, the value highly depended on the loading on the tape, which led to significant uncertainty and discontinuity in the absorption Å ngström exponent compared to using Tape 8060. A method was proposed to effectively correct the historical datasets of σabs and the absorption Å ngström exponent by using the AE33 with Tape 8050. This work provides insight into the quality of measured absorption data when filter-based measurement technology is applied. © The Author(s).

Gaseous dicarboxylic acids (diacids) are suggested to participate in atmospheric new particle formation via bonding with sulfuric acid (SA), ammonia (NH3), amines, and other molecules. However, there is a lack of observational evidence for the involvement of diacids in particle nucleation. Comprehensive measurements were conducted at a rural site of the North China Plain in winter, and unexpectedly high nucleation rates (JOBS, 30.5-839.7 cm-3 s-1) were observed under low SA levels (0.7 × 106 to 4.4 × 106 cm-3). Neither SA-NH3 nor SA-dimethylamine (DMA) mechanisms could fully explain the JOBS. Gaseous diacid monomers and dimers and diacid-SA-DMA clusters were identified in this study. The JOBS values were enhanced by a factor of 5 to 10 as the signal intensities of diacids increased 4-fold. Products of diacid signals and SA concentrations showed a positive correlation with the JOBS (Pearson's correlation coefficient = 0.72). Experimental evidence was found that succinic acid competes with the second SA molecule for addition to the SA·DMA cluster. The concentrations of diacids were estimated to be 1-3 orders of magnitude higher than those of SA. We propose that diacids could actively participate in particle nucleation and may dominate the initial steps under high [diacids]/[SA] ratios. Copyright © 2020 American Chemical Society.

To clarify the aerosol optical properties under different pollution levels and their impacting factors, hourly organic carbon (OC), elemental carbon (EC), and water-soluble ion (WSI) concentrations in PM2.5 were observed by using monitoring for aerosols and gases (MARGA) and a semicontinuous OC/EC analyzer (Model RT-4) in Wuhan from 9 to 26 January 2018. The aerosol extinction coefficient (bext) was reconstructed using the original Interagency Monitoring of Protected Visual Environment (IMPROVE) formula with a modification to include sea salt aerosols. A good correlation was obtained between the reconstructed bext and measured bext converted from visibility. bext presented a unimodal distribution on polluted days (PM2.5 mass concentrations > 75 μg•m-3), peaking at 19:00. bext on clean days (PM2.5 mass concentrations < 75 μg•m-3) did not change much during the day, while on polluted days, it increased rapidly starting at 12:00 due to the decrease of wind speed and increase of relative humidity (RH). PM2.5 mass concentrations, the aerosol scattering coefficient (bscat), and the aerosol extinction coefficient increased with pollution levels. The value of bext was 854.72 Mm-1 on bad days, which was 4.86, 3.1, 2.29, and 1.28 times of that obtained on excellent, good, acceptable, and poor days, respectively. When RH < 95%, bext exhibited an increasing trend with RH under all pollution levels, and the higher the pollution level, the bigger the growth rate was. However, when RH > 95%, bext on acceptable, poor and bad days decreased, while bext on excellent and good days still increased. The overall bext inWuhan in January was mainly contributed by NH4NO3 (25.2%) and organic matter (20.1%). The contributions of NH4NO3 and (NH4)2SO4 to bext increased significantly with pollution levels. On bad days, NH4NO3 and (NH4)2SO4 contributed the most to bext, accounting for 38.2% and 27.0%, respectively. © 2019 by the authors.

Secondary organic aerosol (SOA) is a major component of aerosols in the atmosphere, which plays a crucial role in climate change, regional pollution and human health. Laboratory simulations are usually used to mimic SOA formation. The most commonly used simulation facilities are environmental chambers and potential aerosol mass (PAM) reactors. Here in this work, we review the studies about influencing factors and mechanisms of SOA formation, as well as the evolution of SOA aging. We summarize the influencing factors on SOA yields, i.e. OH exposure, NOx level, and the loading and chemical composition of seed particles. The effects of NOx level (i.e. VOCs/NOx) and OH exposure are nonmonotonic. The NOx level influences the fate of RO2 radicals, so SOA yields will increase and then decrease with the addition of NOx. Similarly, the increase of OH exposure affects the major oxidation mechanism from functionalization to fragmentation, leading to the up and down trend of SOA yields. The higher seed particle loading provides more surface area for condensable products and then increases the SOA yields. The particle acidity favors the uptake process for gas-phase products and promote the SOA formation via further reactions in the condense phase. Trace components e.g. transition metals and minerals can be involved in the SOA formation and aging by catalysis or affecting the uptake of oxidants and their products. Chambers and PAM reactors are usually used to explore SOA formation potential of different sources. SOA formation potential from vehicles will be influenced by engine types, engine loading and composition of fuel. The highest SOA enhancement ratio (SOA/POA) from gasoline engines is about 4~14, when the equivalent photochemical days are 2~3 d. The SOA production mass from gasoline vehicles is from about 10~40 to 400~500 mg/kg fuel. The SOA formation potential is about 400~500 mg/kg fuel. The largest SOA enhancement ratio for biomass burning is 1.4~7.6, which occurs at 3~4 photochemical days. The SOA enhancement ratio from ambient air differs from region to region. However, the highest ratios all occur at the photochemical age of about 2~4 d. We summarize the SOA characteristics evolution with aging. Oxidation state of particles will increase with OH exposure. Changes of H/C and O/C with increasing OH exposure can be plotted in the Van Krevelen diagrams. The slopes of fitted curve range from -1 to 0, indicating OA evolution chemistry involving addition of carboxylic acids or addition of alcohols/peroxides. In addition, the volatility and hygroscopicity of oxidized OA will be higher than primary organic aerosols. In the future, more studies should be focused on developing new technologies to measuring the oxidized intermediate products at a molecular level. Also the researches on the mechanism of SOA formation from complex precursors are also crucial to understand the SOA formation at real atmosphere. © 2020 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.

Brown Carbon (BrC) aerosols scatter and absorb solar radiation, directly affecting the Earth's radiative budget. However, considerable uncertainty exists concerning the chemical mechanism leading to BrC formation and their optical properties. In this work, BrC particles were prepared from mixtures of small alpha-dicarbonyls (glyoxal and methylglyoxal) and amines (methylamine, dimethylamine, and trimethylamine). The absorption and scattering of BrC particles were measured using a photoacoustic extinctometer (405 and 532 nm), and the chemical composition of the alpha-dicarbonyl-amine mixtures was analyzed using orbitrap-mass spectrometry and thermal desorption-ion drift-chemical ionization mass spectrometry. The single scattering albedo for methylglyoxal-amine mixtures is smaller than that of glyoxal-amine mixtures and increases with the methyl substitution of amines. The mass absorption cross-section for methylglyoxal-amine mixtures is two times higher at 405 nm wavelength than that at 532 nm wavelength. The derived refractive indexes at the 405 nm wavelength are 1.40-1.64 for the real part and 0.002-0.195 for the imaginary part. Composition analysis in the alpha-dicarbonyl-amine mixtures reveals N-heterocycles as the dominant products, which are formed via multiple steps involving nucleophilic attack, steric hindrance, and dipole dipole interaction between alpha-dicarbonyls and amines. BrC aerosols, if formed from the particle-phase reaction of methylglyoxal with methylamine, likely contribute to atmospheric warming.