太原市PM2.5积累特征及重污染天气成因分析

收集了太原市2014-2018年秋冬季（10月-翌年2月） PM_2.5、SO₂、NO₂和CO浓度数据以及对应时刻气象资料，基于逐日PM_2.5在16：00-01：00时的变化将其分为消散过程、慢速积累过程和快速积累过程，从PM_2.5积累的角度分析了太原市PM_2.5的污染特征及影响因素，并将其运用于重污染天气形成过程的探讨.结果表明，太原秋冬季慢速积累过程占比最高为44%，快速积累过程占27%，消散过程占29%.10月以慢速积累为主占比超过60%，11和12月快速积累占比最高接近40%，1、2月慢速积累再次占主导地位；快速积累过程占比最高的年份为2014年和2016年均超过35%，慢速积累和消散占比最高的年份均为2017年.慢速积累状态下，二次污染物的生成有助于PM_2.5的积累速率增加；快速积累状态下一次污染物对PM_2.5积累速率影响更明显；发生快速积累时，来自临汾、晋城等东南方向区域输送显著增加.太原市重污染天气的形成过程以慢速积累为主，占比77%.重污染天气下，市区多以硫酸盐和硝酸盐复合污染为主，而郊区以硝酸盐污染为主.

Accumulation characteristics of PM2.5 and the causes of serious pollution weather in Taiyuan city, China

Air quality and synchronous meteorological data of Taiyuan city during 2014-2018 (October to February of the next year) were collected, including the concentrations of PM_2.5, SO₂, NO₂ and CO in autumn and winter. According to the change process of PM_2.5 from 16:00 to 0:00 divided into dissipation, slow accumulation and fast accumulation processes based on the accumulation rate, the accumulation characteristics of PM_2.5 and influencing factors were analyzed and applied to discussing the formation of heavy pollution weather. The results show that, the slowest accumulation process in autumn and winter of Taiyuan accounts for 44%, the fast accumulation process accounts for 27% and the dissipation process accounts for 29%. The slow accumulation accounted for more than 60% in October, and the rapid accumulation accounted for nearly 40% in November and December, but slow accumulation dominate it again in January and February. The fast accumulation process accounted for over 35% in 2014 and 2016, while slow accumulation process and dissipation process dominate it in 2017. In the slow accumulation state, the secondary pollutants contribute significantly to the PM_2.5 accumulation rate, while the primary pollutants contribute more in the fast accumulation state. When rapid accumulation occurred, the transportation from southeast regions such as Linfen and Jincheng city increased significantly. Almost 77% of the serious pollution weather was caused by slow accumulation. Under such weather, the primary pollutants in urban area were sulfate and nitrate, while nitrate was primary in suburban area.