中原城市冬季两次重污染形成机制及来源

为揭示郑州市冬季空气污染过程及形成原因,选取郑纺机国控站点为采样点,探讨2019年12月郑州大气污染物浓度和主要气象参数特征,对比不同污染阶段PM_2.5水溶性离子、元素和碳质组分浓度变化,并利用空气质量模型模拟结果,分析采样期间污染源排放与区域传输对采样点PM_2.5质量浓度的贡献.结果表明,采样期间第一次和第二次重污染形成和消散过程略有差异,分别呈现出"缓慢累积、缓慢清除"和"缓慢积累、快速清除"的特征.第一次和第二次重污染时段NO₃^-、SO₄^2-和NH₄⁺质量浓度占PM_2.5比值达到41.5%和46.2%,OC/EC比值分别为4.0和4.5,二次气溶胶颗粒的大量生成是两次重污染形成的主要原因.采样期间本地、东部、南部、西部和北部区域对采样点PM_2.5浓度贡献占比均值分别为58.0%、2.4%、6.7%、6.9%和12.7%,第一次重污染是本地污染物排放和外来源区域传输共同作用的结果,期间西部和南部区域及外来工业源贡献占比有所升高;而第二次重污染则主要受到本地大气污染物累积的影响,期间交通源、扬尘源和燃煤源污染贡献骤增,外部区域对采样点PM_2.5浓度的影响有所减弱.

Formation Mechanism and Source Analysis of Two Heavy Pollution Periods in Winter in a Central Plains City

To reveal the process and cause of air pollution in winter in Zhengzhou, Zhengfangji Station was selected as the sampling point to discuss the concentration of air pollutants and the characteristics of meteorological parameters in December 2019, in Zhengzhou. The concentration changes in PM_2.5 water-soluble ions, elements, and carbon components in different pollution stages were compared, and air quality model simulation results were used to analyze emissions from pollution sources and regional transmission during sampling of the PM_2.5 mass concentration at the sampling point. The results showed that there was a slight difference in the process of formation and dissipation of the first and second heavy pollution occurrences, showing the characteristics of "slow accumulation, slow removal" and "slow accumulation, fast removal", respectively. The mass concentration of NO₃^-, SO₄^2-, and NH₄⁺ accounted for 41.5% and 46.2% of PM_2.5, and the OC/EC ratios were 4.0 and 4.5 in the first and second heavy pollution periods, respectively. The formation of secondary aerosol particles was the main reason for the formation of heavy pollution. During the sampling period, the average contributions of local, eastern, southern, western, and northern regions to the PM_2.5 concentration of the sampling point were 58.0%, 2.4%, 6.7%, 6.9%, and 12.7%, respectively. The first heavy pollution period was the result of combined locally sourced pollutant emission and externally sourced regional transmission, during which the contribution from western and southern regions and external industrial sources increased. The second heavy pollution period was mainly affected by the accumulation of local air pollutants, during which the contribution of traffic, dust, and coal-fired sources increased sharply, and the impact of external areas on the PM_2.5 concentration of sampling point decreased.