近年来，我国快速的城市化和工业化进程，能源消耗迅猛增长，污染物排放量巨大，导致大气细颗粒物（PM_2.5）污染问题尤为突出，呈现区域复合型污染特征，特别是京津冀所处的华北地区。灰霾天气频繁的出现，不仅给公众的生产生活及身体健康造成极大的危害，而且对区域乃至全球的气候有重要的影响。

二次气溶胶特别是二次有机气溶胶（SOA）对重污染事件PM_2.5浓度有重要贡献，模型模拟是研究SOA的重要手段之一，由于SOA的理化特性和形成机制复杂，SOA模拟机制尚不完善，其模拟结果仍有很大的不确定。本研究选取北京城区冬夏污染过程，进行一系列情景分析实验，基于三维空气质量模型（CAMx）中双产物法和挥发区间法（VBS）两种模拟机制的模拟结果，分析多个因素对模拟结果的影响，分析大气氧化剂的收支循环特征，分析SOA前体物对区域大气氧化剂、二次无机组分的影响，分析SOA、O₃、硝酸盐的浓度与人为源挥发有机物（AVOCs）、NO_x排放量的响应关系。最后解析SOA的污染源和区域传输贡献率，并分析其受模拟机制的影响，以期为科学地制定区域联防联控措施提供理论依据。主要研究结果如下：

（1）对比SOA浓度的模拟值与OC/EC最小比值法的估算值，在7月份模拟时段模型整体上可以模拟出SOA变化趋势和浓度水平，但在1月份重污染时段SOA浓度的峰值时段，模拟值有明显的低估。SOA浓度不仅明显受光化学过程影响，同样受不利气象条件的影响。在增加中等挥发有机物（IVOCs）排放源和多级老化过程后，模拟结果显著提高，特别是浓度较高的河北南部和河南北部等地区。SOA产率、氧化剂水平、NO_x浓度、老化速率等均有不同程度的影响，尤其是前体物排放量和氧化剂水平的影响较大。

（2）HO_x循环过程中OH自由基的生成量占主要部分，表明OH自由基从生成到去除经过多次链循环反应过程，HO_x自由基通过与NO、VOCs等污染物反应得以循环和互相转换，并不断生成NO₂。O₃的去除速率大于生成速率，表明O₃除了本地生成外，也受区域传输的影响。华北城市地区自由基链长高于郊区，表明城区自由基循环过程中产生的量大于新生的，从而有更高的大气氧化性。天然源挥发有机物（BVOCs）排放量的增加提高了区域大气氧化剂和二次无机组分的浓度，气温的升高提高BVOCs排放量，以及SOA、O₃的浓度，受气粒分配、酸碱平衡影响，硝酸盐和铵盐浓度降低，硫酸盐浓度升高。

（3）分析人为源VOCs、NO_x协同减排对SOA、O₃和硝酸盐的影响，O₃和SOA浓度均呈现明显非线性变化的特征，随VOCs排放量的增加而增加，而随NO_x排放量增加呈现先升高后下降的变化趋势，不同AVOCs/NO_x减排比例的结果表明短时期内应当加强AVOCs的减排，AVOCs/NO_x减排比例高于1:1情况下，三种污染物的浓度均可降低。

（4）修改CAMx模型源解析模块，使源示踪法兼容VBS机制。POA的挥发性使其区域传输贡献率降低，从而应该更关注本地及周边地区的排放控制，VBS机制提高ASOA模拟浓度和区域传输贡献率，单萜烯（TERP）与NO₃自由基的反应也提高了BSOA的区域传输贡献率。

In recent years, rapid urbanization and industrialization process has caused a rapid increase in energy consumption and huge emissions of pollutants in China. The problem of atmospheric fine particulate matter (PM_2.5) pollution is particularly prominent, showing regional complex pollution characteristics, especially in North China where Beijing, Tianjin and Hebei are located. The frequent occurrence of haze weather, which not only causes great harm to the public's production and life and physical health, but also has an important impact on regional and global climate.

Secondary aerosols, especially secondary organic aerosols (SOA), have made important contributions to the PM_2.5 concentration of heavy pollution events. Model simulation is one of the important methods for studying SOA. Due to the complex physical and chemical characteristics and formation mechanism of SOA, the SOA simulation mechanism is not perfect, and the simulation results are still very uncertain. This study selects the winter and summer pollution process in urban Beijing, conducts a series of scenario analysis experiments, and bases on the simulation results of the two product method and the volatile basis set method(VBS) in the three-dimensional air quality model(CAMx), analyzes the effects of multiple factors on the simulation results, the characteristics of the budget cycle of atmospheric oxidants, the effect of SOA precursors on regional atmospheric oxidants and secondary inorganic components, and the response relationship between SOA, O₃, nitrate concentrations and anthropogenic volatile organic compounds (AVOCs), NO_x emissions. And finally analyzes the SOA pollution sources and regional transmission contribution rates, and the impacts of simulation mechanism on the results, with a view to providing a theoretical basis for scientifically formulating regional joint prevention and control measures. The main conclusions in this thesis are summarized as follows:

 (1) Comparing the simulated value of SOA concentration with the estimated value of the OC / EC minimum ratio method, the model can simulate the trend and concentration level of SOA on the whole during the simulation period in July, while the simulated value is significantly underestimated during the peak period of the SOA concentration in January. The SOA concentration is not only significantly affected by the photochemical process, but also affected by adverse weather conditions. After increasing the emission sources of Intermediate volatile organic compounds (IVOCs) and the multi-stage aging process, the simulation results have improved significantly, especially in areas such as southern Hebei and northern Henan with higher concentrations. The SOA yield, oxidant level, NO_x concentration, and aging rate all have different effects on the simulation results, especially the precursor emissions and oxidant levels have a greater impact.

(2) The amount of OH radicals generated during the HO_x cycle accounts for the main part, it shows that OH radicals undergo multiple chain cycle reaction processes from generation to removal, HO_x radicals are circulated and converted to each other by reacting with NO, VOCs and other pollutants, and continuously generate NO₂. The removal rate of O₃ is greater than the generation rate, indicating that in addition to local generation, O₃ is also affected by regional transmission. The free radical chain length in North China is higher than that in suburbs, it shows that the amount of free radicals generated in urban areas is greater than that of nascent ones, and thus has higher atmospheric oxidation. The increase in biogenic volatile organic compounds (BVOCs) emissions increased the concentration of atmospheric oxidants and secondary inorganic components in urban areas, and the increase in air temperature increased the BVOCs emissions, as well as the concentratio-ns of SOA and O₃. The effects of gas-particle distribution and acid-base balance reduce the concentration of nitrate and ammonium and increase the concentration of sulfate.           

(3) Analyzing the impact of the collaborative reduction of AVOCs and NO_x on SOA, O₃ and nitrate concentrations, the O₃ and SOA concentrations both show markedly non-linear changes, which increase with the increase of VOCs emissions, and show a trend of increasing first and then decreasing with the increase of NO_x emissions. The results of different AVOCs/NO_x emission reduction ratios indicate that the reduction of AVOCs should be strengthened in a short period of time. When the AVOCs /NO_x emission reduction ratio is higher than 1: 1, the concentrations of all three pollutants can be reduced.

 (4) Modifying the source apportionment module of CAMx model to make the source tracing method compatible with the VBS mechanism. The results show that the volatility reduces the regional transmission contribution rate of POA, so more attention should be paid to the control of local and surrounding area emission. The VBS mechanism improves the simulated concentration and regional transmission contribu- tion rate of ASOA, and the reaction of monoterpene (TERP) with NO₃ radicals increases the regional transmission contribution rate of BSOA.