中山市旱季霾特征及数值模拟分析

Characteristics and numerical simulation on the haze in dry season over Zhongshan

利用观测数据、Hysplit后向轨迹模式以及WRF-CMAQ模式对中山市旱季霾特征进行模拟分析.中山市霾污染的天气形势以大陆高压型为主.当相对湿度在71%~90%时,气溶胶浓度和能见度的负相关性最显著,且当能见度减小到5 km以下时,PM2.5浓度的大幅减小才能使能见度略有好转.最有可能引起中山发生霾天气的两条污染带,一条是沿中山至湖南南部,另一条是沿中山到粤东地区.WRF-CMAQ模式能较好地模拟出2014年1月份中山PM2.5浓度、能见度的变化趋势以及广东省区域内灰霾的污染过程.在气溶胶质量权重及消光贡献中,硫酸盐的比重最高,在高相对湿度下,二次气溶胶的消光权重超过80%.通过中山PM2.5过程分析发现,在霾过程,无冷空气时PM2.5主要来自气溶胶反应、排放源和水平平流,贡献率分别为35%、15%和10%,有冷空气时水平平流的贡献最大,达37%;在清洁过程,无冷空气时气溶胶主要靠水平平流和干沉降清除,贡献率分别为-39%和-14%,有冷空气时清除以水平平流和垂直对流、扩散为主,贡献率分别为-29%和-25%,说明不同天气条件下霾的污染和清洁机制有着明显差别.

This study investigated the characteristics of haze pollutions in dry season over Zhongshan based on observation data,Hysplit model and WRFCMAQ model. Observation data revealed that haze pollution usually happened when high pressure system was dominated. Low visibility was closely correlated with aerosol concentration when relative humidity maintained between 71% ~ 90%. In addition,under low visibility conditions,especially when visibility was less than 5 km,substantial reduction of PM2.5was the only way to improve air quality. Backward trajectory analysis indicated that there were two pollutant transport channels during haze days in Zhongshan,one from southern Hunan and the other from eastern Guangdong. WRF-CMAQ simulations can well reproduce PM2.5concentration,visibility as well as the haze event process within Guangdong. Sulfate contributed the most to PM2.5and the extinction contribution of secondary aerosol was more than 80% under high relative humidity. The process analysis demonstrated that the formationmechanism of aerosol was different under different weather conditions. On haze days without cold air,aerosol processes,emissions,and horizontal transport contributed 35%,15%,and 10% to PM2.5,respectively. Horizontal transport increased to 37% when cold air arrived. On clear days without cold air,horizontal transport and dry deposition played significant roles in aerosol removal,while when cold air arrived,horizontal transport and vertical transport were the main factors for haze removal.