上海城区PM_(2.5)中有机组分及硝基芳香化合物分布特征

Characteristics of Nitroaromatic Compounds in PM_(2.5) in Urban Area of Shanghai

硝基芳香化合物(NACs)是细颗粒物中含氮化合物的重要组成部分,研究其在大气中的污染特征和季节变化,有助于表征大气细颗粒物中含氮有机化合物特性,并为城市氮氧化物削减提供科学支撑.采集并分析了上海城区2018年3月~2019年2月大气PM_(2.5)样品,采用超高效液相色谱-轨道阱质谱(UPLC-Orbitrap MS)在PM_(2.5)样品中定性检测到了2439~3695个有机物,内标法定量了9种NACs,春季ρ(NACs)范围为3.12~16.8 ng·m^(-3),平均值为9.31 ng·m^(-3);夏季ρ(NACs)范围为1.05~9.70 ng·m^(-3),平均值4.16 ng·m^(-3);秋季ρ(NACs)范围为2.87~36.27 ng·m^(-3),平均值9.84 ng·m^(-3),冬季ρ(NACs)范围为4.83~56.23 ng·m^(-3),平均值为22.37 ng·m^(-3).9种硝基芳香化合物中,4个季节均以4-硝基苯酚为主,所占质量分数大于25%.夏季5-硝基水杨酸质量分数为36%,冬季的质量分数为19%,季节性变化显著.经相关性分析,上海夏季NACs浓度与大气氧化性相关较好,说明以二次生成为主,冬季的生物质燃烧和机动车排放是大气NACs的主要来源.

Nitroaromatic compounds(NACs)are an important class of nitrogen-containing compounds in fine particles.The investigation of characteristics and seasonal variation of NACs in PM_(2.5) increases our knowledge about nitrogen-containing compounds and contributes to the scientific basis in formulating reduction policies of NOx in urban areas.In this study,we analyzed the chemical composition of PM_(2.5) samples collected from March 2018 to February 2019 in an urban location in Shanghai.A total of 2439-3695 organic molecular formulas were detected using UPLC-Orbitrap MS.Nine NACs were quantified using an internal standard method.In spring,ρ(NACs)ranged from 3.12 to 16.76 ng·m^(-3),and the average concentration was 9.31 ng·m^(-3).In summer,it ranged from 1.05 to 9.70 ng·m^(-3),and the average value was 4.16 ng·m^(-3).In autumn,it ranged from 2.87 to 36.27 ng·m^(-3),and its average was 9.84 ng·m^(-3).In winter,it ranged from 4.83 to 56.23 ng·m^(-3),and the average was 22.37 ng·m^(-3).4-Nitrophenol accounted for more than 25%of the quantified NACs in different seasons.In summer,the concentration of 5-nitrosalicylic acid accounted for 36%,but it decreased to 19%in winter.NACs in summer mainly originated from secondary formation,as evidenced by their clear correlation with the oxidant level,whereas biomass burning became the main source of NACs in winter.