[Seasonal Variation and Source Analysis for PM_2.5, 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.