天气形势对2014—2018年关中地区各季节空气质量的影响

Influence of synoptic situations on the air quality of different seasons in the Guanzhong basin from 2014 to 2018

天气形势是驱动大气污染物变化的最初动力,其与大气污染有着密切联系。探究天气形势对各季节空气质量的影响,可为污染防控提供一定的指导意见。本文利用NCEP-FNL再分析资料、环境监测数据,研究了天气形势对2014—2018年关中地区各季节空气质量的影响。结果表明:春、秋、冬季“槽西南型”和“高压东南型”对大气污染物浓度减小的影响幅度最大,夏季“低压北部型”和“过渡型”对臭氧最大8小时浓度(O_(3_8h_max))减小的影响幅度最大,在各季节出现以上天气形势时,空气质量一般较好;其余天气形势对大气污染物浓度变化的影响幅度基本均为正值。各年份各季节有利天气形势下污染物浓度均低于不利天气形势;春季、秋季和冬季有利天气形势下的PM_(2.5)、PM_(10)浓度相较不利天气形势下分别减少64.93%、57.14%,55.30%、49.50%和46.61%、34.63%。夏季(O_(3_8h_max))在有利天气形势下相较不利天气形势下降28.80%。对天气形势与大气污染物浓度变化趋势的分析表明:2014—2018年在各季节均呈现出当有利天气形势天数增加(不利天气形势天数减少)时,污染物浓度下降;当有利天气形势天数减少(不利天气形势天数增加)时,污染物浓度出现上升的规律。而在2016年秋季出现的有利天气形势天数较2015年增加,但污染物平均浓度却高于2015年的现象,主要可能是由于沙尘天气增加所导致的。

Background,aim,and scope Elevated atmospheric pollutants,such as particulate matter(PM)and ozone(O_(3)),exert negative impacts on human health and the environment.The worsening O_(3) pollution in the Guanzhong basin(GZB)has attracted widespread attention of the public and scholars.Previous studies have demonstrated that meteorological conditions play a substantial role in the formation,transformation,diffusion,transport,and removal of atmospheric pollutants.When pollutant emissions remain unchanged,the transformation of the atmospheric chemical state mainly depends on meteorological conditions.Recent studies on the influence of synoptic situations on air quality mostly focused on the winter season in the Beijing-Tianjin-Hebei region,Yangtze River Delta,and Pearl River Delta.This study attempted to investigate the evolution characteristics of air quality and its possible relationship with meteorological conditions in the GZB in all four seasons from 2014 to 2018.Materials and methods Using the NCEP-FNL reanalysis data,the large-scale synoptic situations influencing the GZB were analyzed in all four seasons from 2014 to 2018.Along with air quality measurements,we further explored the evolution characteristics of air quality and its connection to the synoptic situations in the GZB in different seasons.Results On average,the PM_(2.5) and PM_(10) concentrations under favorable conditions in spring,autumn,and winter were 64.93%,57.14%,55.30%,49.50%,46.61%and 34.63%lower than those under unfavorable conditions,respectively.The maximum daily average 8 h O_(3) concentration under favorable conditions was 28.80%lower than that under unfavorable conditions in summer.Discussion The prevailing synoptic situations in the four seasons were quite different.In spring,the main synoptic situations included“north-low”and“southwest-trough”.In summer,“north-low”and“inland-high”were the prevailing synoptic situations.In autumn,the predominant synoptic situations were“north-low”and“inland-high”.In winter,the prevailing synoptic conditions were“north-low”,“southeast-trough”,and“inland high”.The air pollutions in the GZB have progressively deteriorated from 2014 to 2018,with the summertime MDA8 O_(3) concentration increasing from about 100μg·m^(−3) to 140μg·m^(−3),the wintertime PM_(2.5) concentration increasing from 74.19μg·m^(−3) to 110.41μg·m^(−3),and the PM_(10) increasing from 135.32μg·m^(−3) to 163.80μg·m^(−3),although the aggressive emission mitigation strategies have been carried out since 2013.In general,the air pollution decreased as the number of days with favorable synoptic situations increased,and vice versa.However,in the autumn of 2016,the number of days with favorable conditions increased compared with that in 2015,but the air pollution levels were higher than those in 2015.This might have occurred because more dust weather occurred in 2016.The unfavorable synoptic situations for O_(3)(“north-low”and“transition”)were quite different from those of PM(“southwest-trough”and“southeast-high”)owing to the different formation mechanisms of O_(3) and PM.Conclusions The air pollutant concentrations under favorable conditions in all four seasons were lower than those under unfavorable conditions.For PM pollution,the favorable synoptic situations included“southwest-trough”and“southeast-high”in spring,autumn,and winter.For O_(3) pollution in summer,“north-low”and“transition”were the two favorable synoptic situations.Recommendations and perspectives Uncertainties may exist in the results owing to the category method of synoptic situations.Future studies should include synoptic analysis at more levels and at more times.More quantitative studies are necessary to further investigate the relationship between meteorological conditions and air quality to provide guidance for air quality forecasting and warning.