北京市大气环境PM2.5和PM1及其碳质组分季节变化特征及来源分析

大气颗粒物是影响我国大多数城市环境空气质量的首要污染物,近年来随着监测技术的进步和采样设备的改进,相关研究对象逐渐从大粒径的PM_10、PM_(2.5)转移到更小粒径的PM_1上.碳质组分是大气颗粒物的重要组成部分.以北京市为研究区域,选取2016年7月、10月及2017年1月、4月作为4个季节的代表月,对大气环境中的PM_(2.5)和PM_1进行采集,分析了二者的质量浓度和季节变化特征.采用两层嵌套气象-空气质量模型系统(WRF-CMAQ)耦合模型对采样时段进行了模拟,分析观测期间PM_(2.5)和PM_1的来源贡献,并使用因子分析法解析了碳质组分的来源.结果表明,PM_(2.5)和PM_1的质量浓度均呈现春、夏、秋、冬这4个季节递增的趋势;PM_1是PM_(2.5)中的主要组成,而且秋冬季节随着灰霾发生频率的增加,PM_1质量浓度占PM_(2.5)的比值明显升高;北京市大气环境中存在明显的二次污染,且SOC更容易在粒径更小的PM_1中积聚.散煤燃烧、机动车尾气排放、居民面源及生物质燃烧排放是北京市大气颗粒物的重要贡献来源;汽油车尾气、柴油车尾气、生物质燃烧和燃煤排放是北京市大气颗粒物中碳质组分的主要来源.

Seasonal Variation and Source Analysis for PM2.5, PM1 and Their Carbonaceous Components in Beijing

Atmospheric particulate matter is the primary pollutant affecting the ambient air quality in most Chinese cities. In recent years, with the progress of monitoring technology and improvement in sampling equipment, the relevant research objects gradually shift from larger particle sizes (PM₁₀ and PM_2.5) to smaller particle size (PM₁). The carbonaceous component is an important part of atmospheric particulate matter. Taking Beijing as the research area, sampling for PM_2.5 and PM₁ was conducted in July and October of 2016, and January and April of 2017 as representative months of four seasons. Mass concentrations and seasonal variation characteristics for PM_2.5 and PM₁ were analyzed. The two-layer, nested, meteorology-air quality coupling model system (WRF-CMAQ) was used to model air circulation during the sampling period and thus analyze the source contributions for PM_2.5 and PM₁. The factor analysis method was also used to analyze the source apportionment of carbonaceous components. The results are as followed:the mass concentrations of PM_2.5 and PM₁ showed an increasing trend by spring, summer, autumn and winter. PM₁ was the main part of PM_2.5, and with the increasing frequency of haze in autumn and winter, the mass concentration ratio of PM₁/PM_2.5 became significantly higher. The authors contend that secondary pollution exists in Beijing''s atmosphere, and SOC is more likely to accumulate in smaller particle size. Widespread coal combustion, vehicle emission, residential emission source and biomass combustion emissions are the major contributors to atmospheric particulates, while gasoline engine exhaust, diesel vehicle exhaust, biomass combustion and coal combustion emission are the main source of carbonaceous components in PM_2.5 and PM₁ in Beijing.