北京典型主城区冬季大气污染特征分析

Characteristics of Air Pollution in a Typical Main Urban Area of Beijing in Winter

利用布设于北京市典型主城区的在线空气质量监测站2015年12月数据(小时质量浓度),探究北京主城区冬季大气污染特征的影响因素。结果表明,冬季主城区大气中O_3污染较轻,而NO_2、NO_x和PM_(2.5)污染较为严重。监测期间NO_2、NO_x和PM_(2.5)最大日均浓度分别是GB3095—2012二级标准浓度限值的2.0、6.4和4.3倍,超标天数分别占总天数的58.1%、48.4%和83.9%;而O_3浓度未超过二级标准限值。相关性分析表明,各污染物及能见度之间都呈现出高度相关性(P<0.01)。其中,主城区环境空气中PM_(2.5)与NO_x和NO_2正相关系数分别高达0.752和0.839,O_3与PM_(2.5)、NO_x和NO_2均在P<0.01水平上呈负相关关系,其中NO_2与O_3负相关性最大(r=-0.772,P=3.124×10-141);能见度与PM_(2.5)、NO_x和NO_2浓度存在显著负相关关系,其中与PM_(2.5)负相关性最大(r=-0.922,P=3.338×10-294),此外,能见度与O_3在P<0.01的水平上呈高度正相关性。工作日NO_2、NO_x和PM_(2.5)小时浓度整体高于周末,污染物浓度曲线均出现2个峰值(浓度峰Ⅰ、浓度峰Ⅱ),工作日浓度峰Ⅰ受06:00—09:00市民工作早高峰出行影响,周末浓度峰Ⅰ受02:00—05:00外埠货车进城影响;工作日和周末的污染物浓度峰Ⅱ都出现在22:00左右。O_3的工作日和周末浓度曲线变化基本一致,均呈"双峰"形态,O_3浓度峰Ⅰ出现在14:00左右,高浓度O_3主要来源于大气光化学作用产生的二次污染,浓度峰Ⅱ出现在04:00、05:00左右,其值约为峰Ⅰ值的40%,可能与平流层臭氧垂直气流输送有关。

Based on the hourly data from the air quality monitoring station during December2015,the winter air pollutioncharacteristics in Beijing typical main urban area was investigated.The results showed that the O3pollution in ambient air wasrelatively light,but NO2,NOx and PM2.5all had a severity of air quality problem.During December,the maximum daily averageconcentrations of NO2,NOx,and PM2.5were2.0,6.4and4.3times of GB3095-2012ambient air quality standard ClassⅡthreshold,respectively.The quantity of NO2,NOx and PM2.5non-attainment days occupied58.1%,48.4%and83.9%of the totalmonth,respectively.The mass concentration of O3attained the standard.SPSS analysis results showed a series of high correlationsamong each certain pollutant and visibility(P<0.01).In main urban area ambient air,PM2.5had high positive correlations both withNOx and NO2(r=0.752and r=0.839,P<0.01).O3had high negative correlations with PM2.5,NOx and NO2(P<0.01),among whichthe negative correlation between O3and NO2was the highest((r=-0.772,P=3.124×10-141).The visibility had high negativecorrelations with PM2.5,NOx and NO2(P<0.01),among which the negative correlation between visibility and PM2.5was the mostsignificant(r=-0.922,P=3.338×10-294).However,there was a positive correlation between the visibility and O3.The hourly massconcentration of NO2,NOx and PM2.5on weekdays was generally higher than that on weekends.Two peak concentration values ofNO2,NOX and PM2.5(PeakⅠand PeakⅡ)appeared both on weekdays and weekends.Affected by a morning peak travelingworking schedule,the weekday PeakⅠappeared during6to9am and the weekend Peak I appeared during2to5am due toheavy-duty truck interstate travel.As the pollutant concentration increased,the PeakⅡfor both weekdays and weekends appearedat about22:00.O3hourly mass concentration fluctuation was found almost the same both on weekdays and weekends.O3curvesduring the weekday and weekend both had a“double peak”shape.Peak I for O3mass concentration,which formed from thesecondary pollution caused by atmospheric photochemical reaction,appeared at around14pm.PeakⅡappeared at around4or5am,which may resulted from the vertical airflow of stratospheric ozone in the early morning.The O3concentration PeakⅡvalueaccounted for40%of the PeakⅠ.