中国城市PM_(2.5)时空动态变化特征分析:2015—2017年

Analysis of spatio-temporal characteristic of PM_(2.5) concentrations of Chinese cities: 2015—2017

近年来我国雾霾事件频发.采用2015—2017年全国329个地级及以上城市PM_(2.5)浓度每小时监测数据,利用全域空间自相关法、自然正交函数和空间描述统计分析的方法,从时空视角来揭示PM_(2.5)浓度的时间动态变化规律以及空间分布特征.研究发现:(1)从全国范围内来看,PM_(2.5)浓度均值逐年降低,降幅最高为夏季,最低为冬季,PM_(2.5)浓度位于40～60μg·m^(-3)之间的城市降幅较大.PM_(2.5)浓度年内表现为"冬高夏低,春秋居中"的时间动态变化规律,且各年PM_(2.5)浓度达优良率不断提高.(2)细颗粒物污染改善程度最大的为德州,京津冀城市群和长三角城市群改善程度居中.全国PM_(2.5)污染范围逐年缩小,但新疆西部和冀鲁豫仍为高污染区,西南和东南沿海地区为低污染区.各区域污染的空间集聚逐年缩小.优良达标率在空间分布特征上无显著变化.(3)"大气十条"部分指标已完成,未来细颗粒物污染治理重点区域仍以京津冀地区为核心.在防治空气污染方面,必须加强区域联防联控机制.

Haze-fog events have frequently occurred in China in recent years. Based on a day-level data-set of PM2.5 concentrations of 329 cities in China from 2015 to 2017,this paper employs the global spatial autocorrelation analysis,empirical orthogonal function,and spatial statistics methods to investigate the temporal dynamics of PM2.5 concentrations and their spatial patterns from the spatio-temporal perspective. The findings are the following.（1）PM2.5 concentrations are getting decrease year by year nationwide. Specifically,in terms of PM2.5 concentrations summer season sees the biggest decrease during the sample period and winter season a slight decrease. Moreover,these cities with PM2.5 concentrations ranging from 40～60 μg·m^（-3） see the largest decrease. In other words,air quality of these cities is getting improve. Besides,it shows a significant temporal pattern of high concentrations in winter,low concentrations in summer and intermediate concentrations in spring and autumn.（2） Regarding PM2.5 concentrations of 329 cities,Dezhou city sees thebiggest decrease. However,Jing-Jin-Ji urban cluster and Yangtze River Delta urban cluster show slight improvements of air quality during the sample period. On the other hand,the area of air pollution displays an ever-narrowing trend. However,the western Xinjiang and Hebei-Shandong-Henan provinces are still highly-polluted areas while the cities of the southwest and southeast China usually have low PM2.5 concentrations,indicating better air quality. Besides,spatial clustering of PM2.5 concentrations is narrowing year by year. Spatial distribution of the excellence rate of air quality of cities shows no remarkable variation.（3） Parts of targets that are set in the air pollution prevention and control action plans have already accomplished. The focus area of air pollution prevention and control should be still on the Jing-Jin-Ji urban cluster. Moreover,the joint efforts should be urgently needed to prevent and control air pollution.