2015-2020年湖北省PM_(2.5)和臭氧复合污染特征演变分析

Characteristic and Trend Analysis of PM_(2.5) and Ozone in Air Compound Pollution in Hubei Province During 2015-2020

为揭示湖北省PM_(2.5)和臭氧(O_(3))复合污染演变特征,基于湖北省17个地市的空气质量国控点和武汉市大气超级站组分监测数据,全面分析湖北省17个地市2015—2020年PM_(2.5)和O_(3)的时空变化特征及相关关系,探讨PM_(2.5)和O_(3)协同效应的成因机理.结果表明:①2015—2020年,湖北省PM_(2.5)显著改善,平均降幅为4.7μg/(m^(3)·a),但冬季负荷仍较高,主要集中于中部地区;O_(3)污染凸显,平均增幅为3.8μg/(m^(3)·a),污染集中在4—10月的暖季,东部地区最严重,近两年超标天数已与PM_(2.5)相当.②湖北省PM_(2.5)和O_(3)关联日趋密切,协同效应显著,日评价指标显示夏季二者呈显著正相关(相关系数为0.57),近两年当PM_(2.5)浓度≤50μg/m^(3)时,相关系数高达0.63;冬季PM_(2.5)浓度与Ox(O_(3)+NO_(2))浓度呈正相关,尤其2020年东部城市二者相关性高达0.46,显示大气氧化性对PM_(2.5)二次污染的重要性.③以武汉市为例,归纳PM_(2.5)和O_(3)复合污染的成因,暖季低PM_(2.5)背景下,高温、中等湿度和弱风速的气象条件以及VOCs和NO_(x)等前体物的高浓度排放,使得受VOCs主控的光化学反应加剧,易造成O_(3)污染,从而加强PM_(2.5)二次生成;冬季高的大气氧化性,叠加不利气象条件,促进颗粒物的二次生成,导致重污染时PM_(2.5)组分以硝酸盐等二次无机组分为主.研究显示,湖北省PM_(2.5)和O_(3)协同控制重点为,在保持现有NO_(x)控制力度基础上强化VOCs控制,遏制暖季和东部区域O_(3)浓度上升,加强冬季和中部PM_(2.5)治理.

In order to reveal the evolution characteristics of compound air pollution,spatiotemporal characteristics of PM_(2.5) and O_(3),as well as their correlation relationships and the formation mechanism of the synergistic effect,were comprehensively analyzed based on the monitoring data in 17 cities in Hubei Province from 2015 to 2020 and the atmospheric superstation in Wuhan.The results indicated:(1)PM_(2.5) pollution was significantly mitigated with a decline rate of 4.7μg/(m^(3)·a),and O_(3) pollution worsened with a growth rate of 3.8μg/(m^(3)·a)and it appeared frequently in the warm season(April to October).In addition,PM_(2.5) concentration in winter was still high,especially in central cities.The number of days with O_(3) exceeding the standard in eastern cities was the same to the number of days with PM_(2.5) exceeding the standard in the past two years.(2)The PM_(2.5) and O_(3) in Hubei Province had an increasingly close relationship,and the synergistic effect was significant.The daily values showed that PM_(2.5) and O_(3) had a significant positive correlation in summer(the correlation coefficient(R)is 0.57),and R was as high as 0.63 when PM_(2.5)≤50μg/m^(3) in the past two years.In addition,there was a positive correlation between PM_(2.5) and Ox in winter,with the highest in eastern cities in 2020(0.46),showing the importance of atmospheric oxidation for the secondary pollution of PM_(2.5).(3)The causes of the synergistic effect of PM_(2.5) and O_(3) in Wuhan were as follows.In the warm season,the intensified O_(3) photochemical reaction was controlled by VOCs due to high temperature,moderate humidity,weak wind and the high emissions of precursors(VOCs and NO_(x))under the background of low PM_(2.5),which will cause O_(3) pollution,thereby enhancing the secondary transformation of PM_(2.5).In winter,high atmospheric oxidation and unfavorable weather conditions promoted secondary aerosol transformation.During the heavy pollution episodes,PM_(2.5) components were mainly secondary inorganic components such as nitrate.(4)The coordinated control in Hubei Province is mainly to strengthen the control of VOCs on the basis of maintaining NO_(x) control,suppress the rise of O_(3) concentration in warm season,especially in the eastern region,and enhance the control of PM_(2.5) in winter,especially in the central region.