大连市大气污染天气特征及污染成因模拟分析

利用大连市2014~2015年地面观测资料、高空地面形势场和2015年12月NCEP/NCAR再分析资料，结合WRF-CMAQ数值模式，对大连市污染天气特征和污染过程的成因进行分析研究.结果表明：2014~2015年大连市共有大气污染日数145d，占20%，大气污染天气过程35个；发生大气污染时的高空形势场主要为槽后脊前的西北气流场，占63%，槽前西南气流场次之，占21%，槽区、脊区各占6%；地面形势场主要表现为风速较小的均压场（68%）和等压线密集风速较大的非均压场（32%）两种气压场.2015年12月出现的5次污染过程中，大气层结均为稳定层结，且近地面水平风速均值较小，对污染物垂直方向和水平方向上的扩散起到抑制作用，导致空气质量恶化；模拟结果发现大连市冬季污染过程中大气气溶胶的的主要成分是硝酸盐、铵盐和硫酸盐等细颗粒物，其中硝酸盐占比最大，且污染过程的增幅最为明显，说明机动车和燃煤排放已对大连市城市污染的形成产生重要影响.

Weather characteristics and simulation analysis on causes of air pollution in Dalian

Based on the observational data, upper air and ground surface synoptic field during 2014~2015, and NCEP/NCAR reanalysis data in December 2015, combined with WRF-CMAQ numerical model, the characteristics and the cause of the air pollution process in Dalian were analyzed. The results showed that there were 145 pollution days, accounting for 20%, and 35pollution processes in Dalian from 2014 to 2015. The upper air circulations during air pollutions were mainly northwest air flow field after the trough (accounting for 63%), and the southwest air flow field before the trough (accounting for 21%). The ground surface synoptic field were mainly in two types, which are uniform pressure field with weak wind (accounting for 68%) and intensive isobars with high-speed wind. The atmospheric stratification was stable, with weak average horizontal wind during 5air pollution processes in December 2015 in Dalian, which suppressed the dispersion of pollutant in the vertical and horizontal directions, leading to the deterioration of air quality. Results of the numerical model simulation showed that nitrate, ammonium and sulfate are the main components of aerosols during the pollution process. And the nitrate provided the first contribution and the most obvious increase during the pollution processes, which means the vehicle emission and coal-fired emission already had important impacts on the formation of urban pollution in Dalian.