随着中国工业化、城市化程度不断提高，以高浓度细颗粒物为特征的霾污染事件在中国频繁发生。霾污染通常被分为一次和二次气溶胶污染，与一次气溶胶相比，二次气溶胶因其可在短时期内快速生成而影响空气质量，因此受到密切关注。二次气溶胶包括二次有机气溶胶（SOA）和二次无机气溶胶（SIA），其中，SIA是大气细颗粒物的重要组成成分，其形成机制复杂，受到大气环境和气象条件的影响显著。因对二次气溶胶的形成机制方面的认识尚存争议，目前已有模式仍不能准确模拟大气中的SIA，且模型结果也会在大多数情况低估真实大气中SIA的质量浓度。自2013年以来，中国开展了多种改善空气质量的环保行动，控制污染的排放显著降低了严重雾霾的发生频率。但随着空气质量的改善，细颗粒物中的SIA和SOA等二次化学组分将会发生变化，进而影响或改变其区域环境和气候效应。为了研究在我国高减排背景下，大气细颗粒物中二次无机盐的变化特征，本论文分别于2018年3月1日至2019年2月23日、2019年11月6日至2020年1月13、以及2019年11月6日至2020年1月13日在北京、广州、山西忻州开展外场观测，主要利用四级杆气溶胶化学组分在线监测仪（Q-ACSM）观测了大气非耐火性细颗粒物（NR-PM_2.5）的化学组成，以分析两种关键SIA（SO₄^2-和NO₃^-）的浓度水平和时空变化，并对其形成机制及爆发性增长的原因进行探究。基于对这些观测数据的分析和研究，本论文取得了以下主要研究结果和结论：

2018-2019年，北京大气细颗粒物中两种主要的SIA（SO₄^2-和NO₃^-）质量浓度占比达37-53%，是NR-PM_2.5重要的化学组分。两种无机盐质量浓度季节变化特征显著，SO₄^2-夏季显著高于冬季，而NO₃^-冬季高于夏季。NO₃^-/SO₄^2-比值也呈明显的季节变化，冬季最大（1.6±1.2），夏季最小（0.7±1.0）。与历史观测结果比较，该比值在2018-2019年有所下降，我们推测这很可能与2016年以来中国氮氧化物减排所导致的NO₃^-生成减弱有关。上述观测结果表明，近年严格的减排措施对改善冬季SO₄^2-污染效果显著，但夏季SO₄^2-污染未得到显著改善，导致夏季SO₄^2-成为细颗粒物中最主要的组分。夏季，NO₃^-/SO₄^2-的比值随相对湿度（RH）的增加而增加，可能与夏季液相生成对NO₃^-的贡献有关。总体上因夏季高浓度的SO₄^2-，NO₃^-/SO₄^2-的比值偏低（最大值为~1.0）。冬季，NO₃^-/SO₄^2-的比值随RH的增加而增加（最高可到~2.2），当RH达到80%以上，该比值有所下降，可能与SO₄^2-的液相途径对其质量浓度的贡献增加有关。NO₃^-/SO₄^2-的比值随环境温度（T）的敏感性分析结果表明，T从-15?C增加至20?C，NO₃^-/SO₄^2-比值变化不大。当T大于20?C时，该比值快速下降，当环境温度达到40?C，该比值接近0, 反映了高温下NO₃^-从颗粒相到气相的气粒分配的增强。典型个例分析表明，北京冬季NO₃^-爆发性增长的主要原因是区域传输作用和边界层（PBL）的变化；而夏季，NO₃^-的日变化主要受N₂O₅水解反应和气-粒分配机制的影响。

本研究通过北京与广州的冬季观测对比，探讨了南北方两个典型大城市冬季二次无机盐质量浓度的变化特征及影响因素。研究结果表明，清洁条件下，北京大气细颗粒物中SO₄^2-和NO₃^-质量浓度（分别为1.23±0.94 μg/m³和1.64±2.43 μg/m³）明显低于广州（分别为5.04±2.29 μg/m³和3.33±2.40 μg/m³），且北京大气细颗粒物中SO₄^2-和NO₃^-的质量浓度百分比（分别为9.6%和12.9%）也低于广州（分别为19.7%和13.0%）。重污染条件下，北京大气细颗粒物中SO₄^2-和NO₃^-质量浓度（15.83±14.69 μg/m³，35.10±25.15 μg/m³）则明显高于广州（9.18±2.98 μg/m³，14.64±8.84 μg/m³），且相对应的质量浓度百分比（12.4%，27.6%）也高于广州（11.0%，17.5%）。上述结果反映了在清洁和污染条件下，二次无机盐浓度水平在两个典型南北方城市的不同形成机制及影响因素。结合环境相对湿度和气象条件分析表明，北京和广州冬季两种二次无机盐对RH的响应呈完全不同的趋势，北京大气中两种二次无机盐浓度随相对湿度增加呈明显增加，而广州则随着相对湿度的增加变化不明显，甚至在高的相对湿度下呈降低（比如SO₄^2-）趋势。进一步结合地面风以及后向轨迹聚类分析表明，北京大气细颗粒二次无机盐浓度高值主要对应其南部区域（河北，山东，山西等）的暖湿污染气团，加之高湿条件下二次无机盐的快速液相过程使北京在重污染期间高相对湿度条件下二次无机盐浓度呈爆发性增长，而广州冬季来自海洋上空的洁净高湿的气团，虽然使观测点环境RH增高，但并不使二次无机盐增长。而在清洁条件下，来自北京西北的洁净干燥气团对降低大气中细颗粒物浓度更有效从而使二次无机盐降至比广州更低。潜在源分析（PSCF）结果表明，广州NO₃^-的主要潜在源分布在观测地以东的沿海地区，SO₄^2-的主要潜在源则分布在观测地以东和观测地的西北向，两种SIA的高值区均集中在深圳市以东的大鹏湾一带。北京冬季NO₃^-的潜在源主要在观测地以南的河北省以及东南部的天津一带，SO₄^2-的潜在源主要分布在观测地西南部的河北省内。

本论文通过北京与山西忻州的夏季观测对比，探讨了北方典型大城市与郊区站点夏季二次无机盐质量浓度的变化特征及影响因素。研究结果表明，夏季，北京大气中SO₄^2-和NO₃^-质量浓度总体高于忻州，观测期间其平均质量浓度分别为16.20±10.83 μg/m³和7.01±7.61 μg/m³（北京）以及12.27±7.51 μg/m³和5.52±5.14 μg/m³（忻州）。重污染期间两种二次无机盐质量浓度在北京均显著高于忻州，而清洁条件下北京则略低于忻州。北京和忻州观测的二次无机盐之和分别占大气总PM_2.5质量浓度的68.7%和65.1%，可见华北区域夏季二次无机盐对大气细颗粒物的主导贡献。两个观测点 SO₄^2-和NO₃^-日变化呈相似特征。结合环境相对湿度分析表明，北京和忻州夏季两种二次无机盐对RH的响应呈相似的变化趋势，其质量浓度均随RH增加呈明显增加，但在RH到达70%以后，其浓度有所降低，这可能受大气湿沉降影响。结合轨迹聚类及潜在源分析，发现夏季忻州和北京都受到来自河北的污染气团的影响。忻州PSCF高值区分别位于观测地的西南部，南部（山西省内）以及东部（河北省）；SO₄^2-的潜在源主要位于东部（河北省）及东北部（山西省内）。北京的NO₃^-潜在源区主要位于观测地的东南部（天津一带）；SO₄^2-的潜在源区主要位于观测点的南部（河北省）与东南部（河北省及天津）。

With the continuous improvement of China's industrialization and urbanization, haze pollution events characterized by high concentration of chemical components in fine particulate matter occur frequently in China. Haze pollution is usually divided into primary aerosol pollution and secondary aerosol pollution. Compared with primary aerosol, secondary aerosol has attracted close attention in recent years because it can be rapidly generated in a short period of time and affect air quality seriously. Secondary aerosols include secondary organic aerosols (SOA) and secondary inorganic aerosols (SIA). SIA is an important component of fine particulate matter in the atmosphere. The formation of SIA is complex, and it is significantly affected by atmospheric environment and meteorological conditions. Due to the controversial understanding of the formation mechanism of secondary aerosols, the current model is still unable to accurately simulate the SIA in the atmosphere, and the model results will still underestimate the mass concentration of SIA in the actual atmosphere in most cases. Since 2013, China has published a variety of environmental protection measures to improve air quality, controlling pollution emissions and significantly reducing the frequency of severe haze. However, with the improvement of air quality, secondary chemical components such as SIA and SOA in fine particulate matter will change, thus affecting or changing its regional environment and climate. In order to investigate the characteristics of secondary inorganic aerosols in atmospheric fine particulate matter under the background of high emission reduction in China, In this paper, field observation was carried out in Beijing, Guangzhou and Xinzhou from March 1, 2018 to February 23, 2019, November 6, 2019 to January 13, 2020 and November 6, 2019 to January 13, 2020 respectively. The chemical components of non-refractory submicron aerosol (NR-PM2.5) in the atmosphere was measured by a quadrupole aerosol chemical speciation monitor (Q-ACSM) to explore the spatiotempoal variation, formation and explosive growth of two key SIA (SO₄^2- and NO₃^-) concentration. Based on the analysis and research of these observed data, the following main research results and conclusions are obtained:

From 2018 to 2019, the mass concentrations of two major SIA (SO₄^2- and NO₃^-) in fine particulate matter in the atmosphere of Beijing accounted for 37-53%, confirmed that they are the important chemical components of NR-PM2.5. The mass concentrations of the two inorganic components showed significant seasonal variation characteristics. SO₄^2- in summer was significantly higher than that in winter, while NO₃^- in winter was higher than that in summer. The ratio of NO₃^-/SO₄^2- also showed significant seasonal variation, with the maximum in winter (1.6±1.2) and the minimum in summer (0.7±1.0). Compared with historical observations, this ratio has decreased in 2018-2019, which we speculate is probably related to the weakening of NO₃^- production caused by the reduction of NOx emissions in China since 2016. Our observation results show that strict emission reduction measures in recent years have a significant effect on the improvement of SO₄^2- pollution in winter, but not in summer, and SO₄^2- has become the most important component of fine particulate matter in summer. Also, the ratio of NO₃^-/SO₄^2- increases with the increase of relative humidity (RH), which may be related to the contribution of aqueous formation pathway to NO₃^- in summer. In general, the ratio of SO₄^2- and NO₃^-/SO₄^2- is low (the maximum value is ~1.0) due to the high concentration of SO₄^2- and NO₃^- in summer. In winter, the ratio of NO₃^-/SO₄^2- increases with the increase of RH (up to ~2.2). When RH reaches more than 80%, the ratio decreases somewhat, which may be related to the increase of contribution of aqueous pathway to the mass concentration of SO₄^2-. The sensitivity analysis of the NO₃^-/SO₄^2- ratio with the ambient temperature (T) shows that when the temperature increases from -15?C to 20?C, the NO₃^-/SO₄^2- ratio does not change much. This ratio drops rapidly when T is greater than 20?C, and approaches 0 when the ambient temperature reaches 40?C, indicating an enhanced partitioning of NO₃^- from the particle phase to the gas phase at high temperatures. The analysis of typical cases shows that the regional transport and the change of boundary layer (PBL) are the main factors for the outbreak of NO₃^- in winter in Beijing. In summer, the diurnal variation of NO₃^- was mainly affected by N2O5 hydrolysis reaction and gas-particle partitioning.

In this study, the variation characteristics and influencing factors of mass concentration of secondary inorganic aerosols in winter in two typical big cities in the south and the north of China were discussed by comparing the observation in winter in Beijing and Guangzhou. The results showed that the mass concentrations of SO₄^2- and NO₃^- in fine particulate matter (1.23±0.94 μg/m³, 1.64±2.43 μg/m³) in Beijing were significantly lower than those in Guangzhou (5.04±2.29 μg/m³, 3.33±2.40 μg/m³) under clean conditions. In addition, the mass concentration percentages of SO₄^2- and NO₃^- in fine particulate matter in Beijing (9.6%, 12.9%) are lower than those in Guangzhou (19.7%, 13.0%). Under heavy pollution conditions, the mass concentrations of SO₄^2- and NO₃^- in fine particulate matter (15.83±14.69 μg/m³, 35.10±25.15 μg/m³) in Beijing were significantly higher than those in Guangzhou (9.18±2.98 μg/m³, 14.64±8.84 μg/m³). The corresponding mass concentration (12.4%, 27.6%) was also higher than that in Guangzhou (11.0%, 17.5%). These results reflect the different formation mechanisms and influencing factors of secondary inorganic aerosol concentration in two typical southern and northern cities under clean and polluted conditions. Combined with environmental RH and meteorological condition analysis shows that both Beijing and Guangzhou, secondary inorganic aerosol on the response of the RH is completely different trends in winter. Two SIA concentration in the atmosphere with the increase of relative humidity was significantly increased in Beijing, while Guangzhou does not change significantly with the increase of RH, even under the high RH. Combined with the surface wind and backward trajectory cluster analysis, the results show that the high concentration of heavy SIA of fine particles in Beijing mainly corresponds to the warm and humid air masses in the southern region (Hebei, Shandong, Shanxi, etc.), and the rapid aqueous phase process of SIA under high RH conditions makes the SIA concentration in Beijing explosive increase under high RH conditions during the heavy pollution period. In winter, the clean and humid air mass over the ocean in Guangzhou increased the RH of the observation site, but did not cause the explosive growth of SIA. Under the clean condition, the clean and dry air mass from northwest of Beijing is more effective to reduce the concentration of fine particles in the atmosphere, so that the SIA is lower than that in Guangzhou. The results of potential source contribution function (PSCF) show that the main potential sources of NO₃^- in Guangzhou are distributed in the coastal area to the east of the observation site, while the main potential sources of SO₄^2- are distributed in the east of the observation site and the northwest of the observation site. The high value areas of the two SIA are concentrated in Dapeng Bay to the east of Shenzhen city. The potential sources of NO₃^- in winter in Beijing are mainly in Hebei Province to the South and Tianjin to the southeast of the observation site, while the potential sources of SO₄^2- are mainly in Hebei Province to the southwest of the observation site.

In this study, the variation characteristics and influencing factors of the mass concentration of secondary inorganic aerosols in summer in typical big cities and suburban stations in northern China were also discussed by comparing the observation of Beijing and Xinzhou, Shanxi in summer. The results show that the mass concentrations of SO₄^2- and NO₃^- in the atmosphere of Beijing are generally higher than those in Xinzhou in summer. During the observation period, the average mass concentrations are 16.20±10.83 μg/m³, 7.01±7.61 μg/m³ (Beijing) and 12.27±7.51 μg/m³, 5.52±5.14 μg/m³ (Xinzhou) respectively. During heavy pollution, two SIA in Beijing was significantly higher than Xinzhou, while under clean conditions, Beijing was slightly lower than Xinzhou. The sum of the SIA observed in Beijing and Xinzhou accounted for 68.7% and 65.1% of the concentration of PM2.5, respectively, indicating the dominant contribution of the SIA in atmospheric fine particulate matter in summer. The diurnal variations of SO₄^2- and NO₃^- at the two samplings showed similar characteristics. Combined with the analysis of environmental RH, the response of the two kinds of SIA to RH in Beijing and Xinzhou in summer shows a similar trend, and the concentrations of the two kinds of SIA increase obviously with the increase of RH. After the RH reaches 70%, the decrease of their concentrations may be affected by the atmospheric wet deposition. Combined with backward trajectory clustering and PSCF analysis, it is found that both Xinzhou and Beijing are affected by the polluted air mass from Hebei in summer. The high value area of PSCF in Xinzhou is located in the southwest, the South (in Shanxi Province) and the East (in Hebei Province); The potential sources of SO₄^2- are mainly located in the East (Hebei Province) and Northeast (Shanxi Province). The potential source area of NO₃^- in Beijing is mainly located in the southeast of the observation site (Tianjin area); The potential sources of SO₄^2- are mainly located in the South (Hebei Province) and Southeast (Hebei Province and Tianjin).