浙江省中西部典型地区PM_(2.5)中二次有机气溶胶示踪物的分布特征

Characterization of Secondary Organic Tracers in PM_(2.5) in a Representative City in Mid-Western Zhejiang Province

为了解我国中小城市地区SOA (二次有机气溶胶)的质量浓度及来源,采集了浙江省中西部典型地区——兰溪市城区和近郊2个站点2016年四季的PM_(2.5)样品,利用GC/MS (气相色谱/质谱)分析了PM_(2.5)中11种指示不同来源的SOA示踪物的质量浓度水平,利用示踪物产率法估算了不同来源前体物对SOC (二次有机碳)的贡献.结果表明:兰溪市PM_(2.5)中ρ(异戊二烯SOA示踪物)的年均值为40. 79 ng/m3,约占检测示踪物总质量浓度的89%;ρ(α-蒎烯SOA示踪物)、ρ(β-石竹烯SOA示踪物)和ρ(甲苯SOA示踪物)的年均值分别为4. 09、0. 36和1. 01 ng/m3.ρ(异戊二烯SOA示踪物)和ρ(α-蒎烯SOA示踪物)存在夏季>秋季>春季>冬季的季节性变化趋势,ρ(β-石竹烯SOA示踪物)为秋季、冬季>春季、夏季,而ρ(甲苯SOA示踪物)的季节性变化不显著,表明不同类型VOCs(挥发性有机物)前体物排放量的季节性变化明显不同.基于示踪物产率法的估算结果表明:夏季异戊二烯等植物源VOCs可能是兰溪市PM_(2.5)中SOA的主要来源;而春季、秋季、冬季甲苯等人为源VOCs是SOA的主要前体物,贡献了兰溪市PM_(2.5)中ρ(SOC)的60%左右.研究显示,减少人为源VOCs的排放对相关地区灰霾及大气细颗粒物污染的防控具有重要作用.

In order to understand the concentrations and sources of the secondary organic aerosols （SOA） in the medium and small cities in China, PM 2.5 samples were collected in four seasons in 2016 at an urban site and a suburban site of Lanxi City, a representative city in the middle-west of Zhejiang Province. The mass concentrations of 11 organic tracers for SOA from different precursors in the samples were measured with GC MS. ρ （SOC from different precursors） and their contributions to the total SOC were estimated with the tracer-based method. Results showed that the annual average ρ （SOA tracers for isoprene） in PM 2.5 in Lanxi City was 40.79 ng/ m^ 3, accounting for about 89% of the quantified SOA tracers. The annual average ρ （α-pinene SOA tracers）, ρ （β-caryophyllene SOA tracers） and ρ （toluene SOA tracers） were 4.09, 0.36 and 1.01 ng /m^ 3, respectively. Similar seasonal trend of summer〉autumn〉spring〉winter was found for ρ （isoprene SOA tracers） and ρ （α-pinene SOA tracers）, while it was higher in autumn and winter than that in spring and summer for ρ （β-caryophyllene SOA tracer）, the seasonal variation of ρ （toluene SOA tracer） was not significant. The differences in the seasonal variations of the SOA tracers indicated that the seasonal emission trends for the target VOCs were different. ρ （SOC） estimation with the tracer-based method suggested that the biogenic VOCs, such as isoprene, might be the main precursors of the summer SOA in Lanxi City, while in spring, autumn and winter, anthropogenic VOCs, such as toluene, contributed about 60% or more of the ρ （SOC） in PM 2.5 in Lanxi City. This study showed that reducing the emissions of the anthropogenic VOCs is very important for controlling haze and fine particles in Lanxi City and other cities.