北京市二次有机气溶胶生成潜势的日变化规律

Diurnal Variation of SOA Formation Potential from Ambient Air at an Urban Site in Beijing

二次有机气溶胶(secondary organic aerosol,SOA)是大气细粒子(PM_(2.5))的重要组成部分.研究实际大气SOA生成潜势的日变化规律对于认知SOA生成转化机制及其对大气细粒子污染的影响具有重要意义.首次使用氧化流动管反应器(oxidation flow reactor,OFR)研究了北京夏季城市大气SOA生成潜势的日变化规律,利用高浓度的羟基自由基(·OH)氧化进入反应器内的环境空气,直接测定SOA的生成潜势.结果表明,一天内,SOA生成潜势的小时均值在3.9~9.4μg·m^(-3)范围内变化,呈现夜间高白天低的趋势,在16:00左右达到最低.SOA生成潜势和甲苯等城市典型挥发性有机物(volatile organic compounds,VOCs)变化趋势一致,而和臭氧浓度反相关.实验结果表明,除了边界层高度变化影响污染物浓度进而影响SOA生成潜势以外,夏季白天强烈的光化学反应导致环境大气VOCs的消耗,对降低环境气体白天的SOA生成潜势值也有重要影响.同国外同类研究相比,北京环境大气由于具有更高的VOCs浓度,其SOA生成潜势要明显高于其他地区,可能对北京地区细颗粒物污染具有重要贡献.

Secondary organic aerosol（SOA） is an important component of atmospheric fine particles（PM_（2.5））.The study of the diurnal variation of SOA formation potential is important for understanding the evolution of SOA and its contribution to fine particle pollution.The oxidation flow reactor（OFR） was used to study the SOA formation potential of ambient air in summer at an urban site in Beijing.The high concentration of OH radicals in the reactor can oxidize the volatile organic compounds（VOCs） and lead to SOA formation.The hour average SOA formation potential varied between 3.9-9.4 μg·m（-3） in a day and had a higher value at night than in the daytime.The lowest value of SOA formation potential was about 3.9 μg·m（-3） observed at 16： 00 in the afternoon.This variation of SOA formation potential is consistent with the typical VOCs,such as toluene,and inversely related to the concentration of ozone.In addition to the impact of change in the height of the boundary layer,experimental data showed that the reduction of VOCs in photo-oxidation in the daytime was an important reason for the decrease of SOA formation potential in daytime.Compared to similar studies in developed countries,the SOA formation potential was higher in Beijing due to the higher concentrations of VOCs and might make an important contribution to the fine particle pollution in Beijing.