大气NR-PM_(1)特性的多尺度演变及其影响机制

Multi-scale evolutions of atmospheric NR-PM_(1) characteristics and its influencing mechanisms

通过采用气溶胶化学组分在线监测质谱仪(ACSM)实时监测了北京市东南城区2021年12月至2022年11月大气非难熔亚微米颗粒物NR-PM_(1)及其组分有机物(Org)、硫酸盐(SO_(4)^(2-))、硝酸盐(NO_(3)^(-))、铵盐(NH_(4)^(+))和氯化物(Cl^(-))浓度,分析研究了NR-PM_(1)及其组分不同时间尺度,特别是污染期间的变化特征,以及影响二次硫酸盐和硝酸盐形成的重要因素.同时,结合正交矩阵因子分析法(PMF)和后向轨迹聚类分析法分别探究了有机气溶胶(OA)不同时段物种的变化特征,以及不同时段气团长距离传输对NR-PM_(1)及其组分的影响机制.结果表明,研究期间NR-PM_(1)年均质量浓度为(7.60±10.35)μg/m^(3),低于2016年以来相应的年均值,并呈现出逐年下降的趋势,不同季节其平均浓度呈现出秋季>春季>冬季>夏季的季节变化特征,不同季节其日变化均呈现出夜间高于白天的特征.NR-PM_(1)物种年均质量浓度呈现出Org>NO_(3)^(-)>NH_(4)^(+)~SO_(4)^(2-)>Cl^(-)的特征,其中Org对NR-PM_(1)的贡献最大,约为41.16%,其后依次为硝酸盐33.05%,铵盐12.47%,硫酸盐11.99%,氯化物最小,约为1.33%.不同季节NR-PM_(1)组分浓度的昼夜变化均较小,NR-PM_(1)及其组分在霾污染天的平均浓度均大于臭氧污染天和清洁天.大气中碱性NH_3的存在以及霾污染天的气象条件更有利于气态前体物的二次转化.不同季节OA物种有所不同,冬季、春季和秋季的二次有机气溶胶(SOA)是OA的主要组分,而夏季一次有机气溶胶(POA)是OA的主要组分,霾污染天和臭氧污染天OA均主要受二次有机物生成的影响.不同季节气团传输途径有所不同,值得注意的是霾污染天主要受东南方向和南方向短距离气团输送的影响,且NO_(3)^(-)对NR-PM_(1)的贡献较大.O_(3)污染天主要受南方向的短距离气团输送的影响,而清洁天以西北方向长距离气团输送为主.

An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was deployed to in situ measure the concentrations of non-refractory submicron particulate NR-PM_(1) and its species as organics Org,sulfate SO_(4)^(2-),nitrate NO_(3)^(-),ammonium NH_(4)^(+)and chloride Cl^(-)at the southeast urban area in Beijing from December 2021 to November 2022,and further investigate the change characteristics of NR-PM_(1) and its species at different time scales,especially during the different pollution periods,and the important factors affecting the formation of secondary sulfate and nitrate.Meanwhile,the positive matrix factorization PMF and backward trajectory clustering analysis were used to study the change characteristics of organic aerosol OA components in the different periods,and the influence mechanism of air mass long-distance transport on NR-PM_(1) and its species in the different periods,respectively.The results showed that the annual average mass concentration of NR-PM_(1) during the study period was (7.60±10.35)μg/m~3,being lower than the corresponding annual average since 2016,and showed a decline trend year by year.The average concentrations of NR-PM_(1)in different seasons showed an obvious seasonal variation characterized by autumn>spring>winter>summer,and the diurnal variations in different seasons followed the order of night>day.The average annual mass concentration of NR-PM_(1) species showed an order of Org>NO_(3)^(-)>NH_(4)^(+)~SO_(4)^(2-)>Cl^(-),among which Org contributed the largest fraction of NR-PM_(1) with about 41.16%,followed by nitrate 33.05%,ammonium 12.47%,sulfate 11.99%,and chloride contributing the lowest fraction with 1.33%.The diurnal variations of NR-PM_(1) concentrations in different seasons were all smaller,and the average concentrations of NR-PM_(1) and its species in haze days were higher than those in ozone pollution days and clean days.The presence of alkaline NH_(3) in the atmosphere and the meteorological conditions during the haze days were more favorable for the secondary transformation of gaseous precursors.The OA components were different in different seasons.SOA in winter,spring and autumn is the main component of OA,while POA in summer is the main component of OA.OA in haze and ozone-polluted days was mainly affected by secondary organic matter.The transport pathways of air mass were different in different seasons.It is noted that the haze pollution days were mainly affected by the short-distance transports of air mass from the southeast direction and the south direction,and NO_(3)^(-)showed a greater contribution to NR-PM_(1).O_(3)-polluted days were mainly affected by short-distance transports of air mass from the south direction,while clean days were mainly affected by long-distance transports of air mass from the northwest direction.