四川盆地PM_(2.5)和O_(3)复合污染特征及相互作用研究

Characteristics and interaction of PM_(2.5) and O_(3) complex pollution in Sichuan Basin

基于四川盆地国控环境监测站近7年(2015—2021年)逐时大气污染监测数据,将其分为两类站点(城区站点、背景站点),分别研究不同维度(年、季、月时间尺度和不同污染水平)下细颗粒物(PM_(2.5))和臭氧(O_(3))复合污染特征及相互作用.结果表明:①四川盆地3个区域(成都平原、川南、川东北)的PM_(2.5)浓度均呈下降趋势,川南地区PM_(2.5)超标天数和平均浓度均高于成都平原和川东北地区;PM_(2.5)月均浓度呈冬春高、夏秋低的“U”型特征.②盆地O_(3)浓度呈波动下降趋势,成都平原O_(3)浓度高于川南和川东北地区;O_(3)月均浓度呈现与PM_(2.5)相反的春夏高、秋冬低的“N”型特征,背景站点略高于城区站点.③两类站点PM_(2.5)与O_(3)的相关性在PM_(2.5)污染期(11月—次年1月)和O_(3)污染期(4—8月)存在显著差异,PM_(2.5)污染期成都平原和川南的背景站点PM_(2.5)与O_(3)呈现较弱的正相关,川东北的城区站点二者则呈现负相关;随着PM_(2.5)污染水平提高,O_(3)逐时浓度日变化范围更大(峰值更高,谷值更低),小时变化率波动幅度增大,且城区站点增大程度大于背景站点.④O_(3)污染期,PM_(2.5)与O_(3)均呈现显著正相关(污染同升同降),相关系数背景站点大于城区站点;随着光化学反应强度增大,二次PM_(2.5)的浓度和贡献率随之升高,一次PM_(2.5)亦表现出更加剧烈的日变化特征.

Based on seven years(2015—2021)of hourly pollutant concentration data from national-controlled environmental monitoring sites in Sichuan Basin,this paper divided the sites into two types(urban and background sites)to investigate the complex pollution characteristics and interaction between PM_(2.5)and O_(3)under different dimensions(yearly,seasonal,monthly and under different pollution levels)respectively.The results showed that:①The PM_(2.5)concentrations in the three regions of the basin(Chengdu Plain,Southern Sichuan,and Northeast Sichuan)showed a downward trend,and the number of days with PM_(2.5)exceeding the standard and average concentrations in Southern Sichuan were higher than those in Chengdu Plain and Northeast Sichuan.The monthly average concentration of PM_(2.5)showed"u"type of high in winter and spring,and low in summer and autumn.②The O_(3)concentration in the basin also showed a downward trend,and the O_(3)concentration in the Chengdu Plain was higher than that in Southern and Northeast Sichuan.The monthly average concentration of O_(3)showed"n"type opposite to PM_(2.5),which was high in spring and summer while low in autumn and winter,and values at the background sites were slightly higher than those in urban sites.③There were significant differences in the correlation between PM_(2.5)and O_(3)at the two types of sites during the PM_(2.5)pollution period(November-January)and the O_(3)pollution period(April-August).That was PM_(2.5)and O_(3)at background sites in Chengdu Plain and Southern Sichuan showed a weak positive correlation during the PM_(2.5)pollution period,while PM_(2.5)and O_(3)at urban sites in Northeast Sichuan showed a negative correlation.With the increase of PM_(2.5)pollution level,the daily variation range of hourly O_(3)concentration was larger(higher peaks,lower troughs),the fluctuation range of hourly change rate increased,and the increase degree of urban sites was greater than that of background sites.④During the O_(3)pollution period,PM_(2.5)and O_(3)showed a significant positive correlation(pollution was rising and falling together),and the correlation coefficient of background sites was greater than that of urban sites.With the increase of photochemical reaction intensity,the concentration and contribution rate of secondary PM_(2.5)increased,and the primary PM_(2.5)also showed more drastic diurnal variation.