降雨过程后北京城区PM2.5日时空变化研究

随着人类环境意识的增强,人们对城市雾霾天气的忧虑与日俱增,PM2.5的时空变化和对人体健康的影响已成为关注的焦点。以往的研究多集中在不同季节或年际的变化,本文通过统计环保局发布的位于北京城区13个逐时浓度监测点降雨前后PM2.5质量浓度,并在城区布设14个采样点昼夜连续监测一次降雨后72 h内PM2.5质量浓度变化情况,研究北京市城区降雨后PM2.5日变化规律及空间分布特征,由此分析降雨对PM2.5日变化规律的影响。同时对比PM2.5与同步气象数据（温度、相对湿度）和交通数据（车辆量、车速）最值频率分布情况,进而对PM2.5日变化特征进行成因分析。随后利用GIS空间分析方法,分析了PM2.5的日空间分布特征。结果表明,降雨对颗粒物的去除作用明显,一次降雨可使PM2.5质量浓度平均下降56.3%。雨后72 h内PM2.5质量浓度均小于60μg·m-3,降雨后1 h内PM2.5质量浓度处于稳定状态,在随后的12 h内PM2.5浓度值都处于下降状态。降雨过程只降低PM2.5的质量浓度值,并不影响其日变化规律。PM2.5的日变化规律以19时为界,表现出明显的昼夜差异。白天的变化规律呈现凹型,夜间的变化规律呈现拱型。PM2.5质量浓度峰值多出现在23时或0时,谷值多出现在下午15时,该特征受气象因素影响较大,受交通源的影响作用不明显。早高峰期间,PM2.5质量浓度变化主要受交通源的影响;晚高峰期间,交通源和气象因素共同影响PM2.5质量浓度。研究区PM2.5日空间分布特征同样存在明显的昼夜差异。白天PM2.5空间分布特征为南部高北部低;PM2.5在夜间的空间分布特征则多表现为四周高、中心低,三环外围区域多为高值区。

Spatial and temporal variation of PM2.5 in Beijing city after rain

With increasing awareness of the environmental protection, residents’ concerns about the city haze weather are increasing at the same time. The spatio-temporal variation of PM2.5 and its impact on human health are becoming the focus of concerns. Previous studies mainly focus on seasonal or yearly variations. This study attempted to explore the characteristics of PM2.5 temporal daily variation and the spatial distribution after rainfall. We collected data of hourly PM2.5 concentrations before and after rainfall in 13 air sampling stations designated by the Beijing Bureau of Environmental Protection and 14 additional samplings sites in Beijing, and analyzed the impact of rainfall on the characteristics of temporal variations of PM2.5. This study further integrated with synchronous meteorological data （temperature, humidity） and traffic data （vehicle volume and speed） to reveal the reasons behind the characteristics of PM2.5 daily variation. The GIS spatial analysis method was subsequently employed to uncover the characteristics of the PM2.5spatial distribution. Results showed that rainfalls efficiently removed particles in the air. A rainfall made the concentration of PM2.5 decreased by an average of 56.3%. PM2.5 concentration was at steady state within 1 hour after rainfall, continued to decline in the next 12 hours and was less than 60μg·m-3 in all 72 hours. The rainfall has significant removal effect on particles with little impact on the diurnal temporal variation curve. The diurnal variation of PM2.5 concentrations exhibited, while the curve was concave type during the day and an arch at night. The peak value appeared at 23 or 0 o’clock and the valley value appeared at 3 pm. This characteristic was greatly influenced by meteorological factors, while traffic contribution is not significant. PM2.5 concentrations were influenced mainly by traffic factors during rush hours in the morning and by both meteorological and traffic factors during rush hours in the evening. The study area on the spatial dis