长三角典型城市PM2.5浓度变化特征及与气象要素的关系

利用长三角地区4个典型城市南京、上海、杭州、合肥2014年4月1日~2015年3月31日的PM2.5监测数据,以及同期MICAPS地面气象要素的观测资料,对该地区PM2.5浓度的变化规律及其与气象要素的关系进行了分析和讨论。结果表明:长三角地区PM2.5浓度总达标率总体表现为夏季最高,冬季最低的态势。4个城市中,上海全年总达标率最高,杭州其次,合肥最低。上海和杭州达标率月变化特征相近,南京和合肥相近;PM2.5逐小时浓度日变化曲线呈现两峰一谷型分布,最大值均出现在早晨,最小值均出现在下午16~17时之间;月平均浓度具有明显的季节变化特征,冬季最高,夏季最低;PM2.5浓度与风速呈现显著现负相关关系,受地面风向影响明显,污染物在主导风的作用下从上游污染源扩散至下风区域;与气温呈现负相关关系;从全年来看,PM2.5浓度与相对湿度呈现负相关关系,高湿度状态更有利于降水从而增加PM2.5湿清除;各个城市PM2.5浓度与气压相关性很弱,并且未通过显著性检验,可见气压是影响PM2.5浓度变化的次要因素;降水对PM2.5清除作用明显。不同城市PM2.5的变化特征及其受气象要素的影响存在差异,主要是由不同城市的地理环境、产业布局以及污染源等因素造成的。

Characteristics of PM2.5 Concentration and its Relations with Meteorological Factors in Typical Cities of the Yangtze River Delta

Based on the observational data of PM2.5 mass concentration and meteorological elements from MICAPS data in Nanjing, Shanghai, Hangzhou and Hefei, four typical cities over the Yangtze River Delta region, from April 1, 2014 to March 31, 2015, the variation of PM2.5 concentration and its relationship with meteorological factors were analyzed and discussed. The results showed that: The total standard-reaching rate of PM2.5 concentration in the Yangtze River Delta was the highest in summer, and the lowest in winter. Among four cities, Shanghai had the highest rate for the whole year, followed by Hangzhou and the lowest in Hefei. The monthly variation characteristics of PM2.5 standard-reaching rate in Shanghai and Hangzhou were similar, and Nanjing and Hefei were similar. The diurnal variation curve of PM2.5 showed a two-peak and one-grain distribution. The maximum values appeared in the morning and the lowest values appeared between 16 and 17 pm; The monthly averaged concentration had obvious seasonal variation characteristics, the highest value in winter, and the lowest in summer; PM2.5 concentration was negatively correlated with wind speed and was affected by the wind direction. Pollutants can diffuse from the upstream pollution source to the downwind area under the dominant wind direction; There was a negative correlation between PM2.5 mass concentration and temperature in the Yangtze River Delta; PM2.5 concentration in the Yangtze River Delta was negatively correlated with the relative humidity during the whole year, and the high humidity was more favorable for precipitation, which caused PM2.5 wet deposition; The correlation between PM2.5 concentration and pressure in each city was very weak, and the significance test was not passed. It can be seen that pressure was a minor factor affecting PM2.5 concentration. Precipitation had obvious scavenging effect on PM2.5. The variation of PM2.5 in different cities and the influences of meteorological factors were also different. It was mainly caused by the geographical environment, industrial distribution and emission sources of different cities.