2013-2015年合肥市PM2.5重污染特征研究

综合利用中国环境监测网公布的合肥市2013-2015年大气污染物浓度数据和合肥市气象站的常规气象资料，以及激光雷达探测资料、公益性行业（气象）专项（GYHY201206011）获得的气溶胶离子成分分析结果，分析了合肥市PM_2.5重污染（日均浓度>150 μg/m3）特征。结果表明:（1）2013-2015年，合肥市PM_2.5浓度和重污染天数空间分布差异明显，东北部多、西南部少，1月各站差异最大。除了低浓度日（日均浓度≤35 μg/m3），PM_2.5浓度都存在明显的日变化，午后低、早晚高，且随着污染程度加重，早上峰值出现时间推后。（2）重污染日臭氧以外的气态污染物浓度都显著上升。（3）重污染日常伴随着霾和轻雾天气，以稳定、小风天气为主，重污染日白天相对湿度偏高、风速偏小，600 m以下的消光系数显著增大且峰值高度降低。（4）重污染日PM_2.5中水溶性无机离子含量增高，其中NO₃-含量的占比增加最多，超过了SO₄2-的占比。 

Characteristics of severe PM2.5 pollution in Hefei during 2013-2015

The air quality data published by the environmental authorities, the meteorological data collected at Hefei observatory during 2013-2015, together with the vertical extinction coefficient data observed by lidar and water-soluble inorganic ions data of aerosols obtained during scientific field experiments were used to analyze characteristics of severe PM_2.5 pollution (daily average PM_2.5 concentration >150 μg/m3) in Hefei. The results show that:(1) the PM_2.5 pollution showed evident spatial differences with more severe PM_2.5 pollution days at sites in northeastern Hefei and fewer pollution days at sites in southwestern Hefei. Monthly variations of severe PM_2.5 pollution days were similar at all sites with the largest difference occurring in January. The PM_2.5 concentration showed an evident diurnal variation with two maxima in the morning and evening respectively, and the morning maximum in severe pollution days often occurred later than in light polluted days; (2) in severe PM_2.5 pollution days, the concentrations of other gas pollutants except O₃ increased obviously; (3) severe PM_2.5 pollution days usually corresponded to haze and light fog, accompanied with light winds and stable stratification. The vertical extinction coefficients of aerosols below 600 m at the noon in severe pollution days were much higher than those in other days, while the occurrence height of maximum extinction coefficient decreased; (4) in severe pollution days, the water-soluble inorganic ions in PM_2.5 became more abundant, and the percentage of NO₃- increased most, exceeding the percentage of SO₄2-. The above results advance our understanding of the role of nitrate in the formation of high level PM_2.5 and are helpful for the forecast and control of PM_2.5 pollution.