• 关键词：PM_2.5  O₃  复合污染  气象因素  天气形势  天津

• 基金项目：天津市科技计划项目（No.18ZXSZSF00160）

• 刘可欣
• 南开大学环境科学与工程学院, 国家环境保护城市空气颗粒物污染防治重点实验室, 天津 300350

• 卢苗苗
• 1. 南开大学环境科学与工程学院, 国家环境保护城市空气颗粒物污染防治重点实验室, 天津 300350;2. 中国气象局-南开大学大气环境与健康研究联合实验室, 天津 300074

• 张裕芬
• 1. 南开大学环境科学与工程学院, 国家环境保护城市空气颗粒物污染防治重点实验室, 天津 300350;2. 中国气象局-南开大学大气环境与健康研究联合实验室, 天津 300074

• 吴建会
• 1. 南开大学环境科学与工程学院, 国家环境保护城市空气颗粒物污染防治重点实验室, 天津 300350;2. 中国气象局-南开大学大气环境与健康研究联合实验室, 天津 300074

• 唐晓
• 1. 中国科学院大气物理研究所大气边界层物理和大气化学国家重点实验室, 北京 100029;2. 中国科学院区域大气环境研究卓越创新中心, 厦门 361021

• 李亚菲
• 南开大学环境科学与工程学院, 国家环境保护城市空气颗粒物污染防治重点实验室, 天津 300350

• 王自发
• 1. 中国科学院大气物理研究所大气边界层物理和大气化学国家重点实验室, 北京 100029;2. 中国科学院大学地球与行星科学学院, 北京 100049;3. 中国科学院区域大气环境研究卓越创新中心, 厦门 361021

• 摘要：天津市PM_2.5-O₃复合污染主要发生在夏秋季，本研究筛选出2017年夏季一次和秋季两次典型PM_2.5-O₃复合污染过程，系统分析污染物变化特征，探究天气形势和主要气象因子的影响.结果表明，3次污染过程PM_2.5与O₃呈现不同程度的正相关性（日均值相关系数达到0.34~0.78），O₃与PM_2.5中硫酸盐和有机碳日均浓度存在较为一致的变化趋势.与非复合污染日相比，复合污染日无机盐占PM_2.5组分的比重增加，增长率为1.9%~7.3%；而碳组分占比减小.复合污染过程发生时，天津地区处于低压槽前或高压后部，近地面弱的偏南风辐合造成较差的大气扩散条件，导致大气污染物的累积.研究结果发现，夏季和秋季PM_2.5-O₃复合污染过程需要适宜的气象条件，温度阈值分别为25~35℃和20~30℃，相对湿度分别为40%~70%和55%~100%.夏秋季复合污染过程关键无机组分及其形成机制有所差异.夏季，日间O₃等强氧化剂对SO₂的气相氧化过程和夜间高湿条件（大约60%）下液相化学反应可能是主导的化学机制，硫酸盐增长率为8.2%.秋季高湿环境（≥80%）不仅促进SO₂向硫酸盐转化，秋季第一次复合污染过程硫酸盐增长4.7%，也促进夜间N₂O₅水解反应等，秋季第二次复合污染过程硝酸盐增长6.0%，两种机制成为秋季复合日PM_2.5显著增长的关键机制.本研究揭示了驱动天津市PM_2.5-O₃复合污染过程发生的适宜气象条件、PM_2.5关键化学组分及其化学过程，为复合污染的成因及协同控制提供了参考.

• Abstract：The PM_2.5-O₃ compound pollution of Tianjin mainly occurred in summer and autumn. In this study, one typical process in summer (Case1) and two processes in autumn (Case2 and Case3) in 2017 were selected to analyze the characteristics of compound pollution and identify the influence of the meteorological conditions. A notably positive correlation between daily average concentration of PM_2.5 (especially sulfate and organic carbon) and O₃ was observed with the correlation coefficients of 0.34~0.78 in the three processes. Compared to non-compound days, the inorganic aerosols comprised an increasing fraction of chemical composition (1.9%~7.3%) in compound days, while the fraction of carbon components decreased. During the compound pollution processes, Tianjin was located in front of the low pressure trough or behind the high pressure. The convergence of weak southerly winds led to adverse atmospheric diffusion, which favored the accumulation of air pollutants. Our results showed that the temperature of about 25~35 ℃ and 20~30 ℃, and the relative humidity (RH) ranges of 40%~70% and 55%~100%, would be suitable conditions for the occurrence of compound pollution in summer and autumn, respectively. The key inorganic components and main chemical processes were different in the three cases. The gas-phase oxidation of SO₂ by high oxidants concentration in daytime and the aqueous-phase chemistry at high RH of 60% at night were the key chemical mechanism of sulfate with an increase of 8.2%. The higher RH of ≥80% in autumn effectively promoted the aqueous formation of sulfate by 4.7% in Case2. Meanwhile, the condition also enhanced the nitrate formation by 6.0% such as the hydrolysis of N₂O₅ at night in Case3. The two formation mechanism became the key mechanism for the significant growth of PM_2.5 on compound days in autumn. The study reveals suitable meteorological conditions and the possible chemical processes of the key PM_2.5 components that drive the formation of compound pollution, which is benefit for synergic control of PM_2.5 and O₃ in Tianjin.

• Key words：PM_2.5  O₃  compound pollution  meteorological condition  weather condition  Tianjin

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