中国东西部典型本底站黑碳气溶胶时空分布及来源分析

Characteristics of spatial and temporal distribution and source apportionment of black carbon aerosols at typical baseline stations in eastern and western China

基于2007-2018年4个代表性大气本底站(临安、上甸子、龙凤山和瓦里关)的逐小时黑碳(black carbon,BC)观测数据和同期气象资料,开展中国东西部BC时空变化特征分析;利用黑碳仪模型和浓度权重轨迹(concentration weighted trajectory,CWT)分析法对比分析了各站点BC的来源类型和潜在源区。结果表明:(1)中国BC质量浓度分布呈现“东高西低”的特点,各站点BC多年平均质量浓度依次为临安站[(3553±2336)ng·m^(-3)]、上甸子站[(2045±1918)ng·m^(-3)]、龙凤山站[(1966±2104)ng·m^(-3)]、瓦里关站[(455±380)ng·m^(-3)]。(2)东西部4个典型本底站点BC质量浓度季节变化和日变化特征不同。东部站点为冬季最高、春秋季次之、夏季最低,而西部站点表现为春季最高、夏季次之、冬季再次之、秋季最低;东部站点BC质量浓度日变化以“双峰型”分布为主,西部瓦里关站呈“昼高夜低”的高山站特征。研究期内,各站BC呈逐年显著下降的趋势,体现了中国大气污染治理的成效。(3)BC主要来自液态燃料的燃烧(简记为“BC liquid”);受冬季采暖影响,夏季BC liquid大于冬季。(4)受亚洲季风影响,不同季节近地面风场对东西部站点BC质量浓度的影响不同,BC潜在来源也不同。东部站冬季潜在源区多在周边大城市群,高值区范围较大;夏季多来自各站偏南方向。西部瓦里关站夏季潜在源区为四川北部城市群,冬季为中国兰州附近和印度北部。

Using the hourly black carbon(BC)mass concentration and the meteorological data from 2007 to 2018 at Lin’an(LA)station,Shangdianzi(SDZ)station,Longfengshan(LFS)station,and Waliguan(Mt.WLG)station,4 typical baseline stations in China,the characteristics of spatial and temporal variations of BC are evaluated in eastern and western China.Combined with the Aethalometer model and the concentration weighted trajectory(CWT)model,the source types and potential source areas of BC are identified.The results are illustrated below.(1)The BC mass concentrations show large fluctuation,referred to as the“high in the east and low in the west”geographical distribution.The annual mean BC mass concentrations at each site are(3553±2336)ng·m^(-3)(LA),(2045±1918)ng·m^(-3)(SDZ),(1966±2104)ng·m^(-3)(LFS),and(455±380)ng·m^(-3)(Mt.WLG).(2)The seasonal variation of BC mass concentration is characterized differently in the east and west of China.In the east,the BC mass concentration is the highest in winter,followed by autumn and spring,and the summer has the lowest BC mass concentration;while in the west,it shows the seasonal variation of BC in the order of spring>summer>winter>autumn.Meanwhile,the diurnal variation is observed.The eastern stations are dominated by the bimodal pattern,whereas the western station(Mt.WLG)is a high-altitude station with a pattern of“high in the daytime and low at night”.During the study period,the BC mass concentrations show a significant decline trend of interannual variation,reflecting the effectiveness of air pollution control in China.(3)The proportion of BC sources is dominated by the burning of liquid fuels(BC liquid).The proportion of BC liquid in summer is higher than that in winter influenced by winter heating.(4)The effect of surface wind fields on BC mass concentrations varies between seasons due to the East Asian monsoon,as well as the potential sources.In winter,the BC in eastern stations mostly comes from the surrounding urban agglomerations with a large scale of high values;in summer,it tends to originate from the southern part of each station.In summer,the high potential source areas of the western station(Mt.WLG)are the northern Sichuan urban agglomerations,while in winter,the BC is mainly from the surrounding areas of Lanzhou in China and northern India.