Analysis of the Characteristics and Sources of Carbonaceous Aerosols in PM _2.5 in the Beijing, Tianjin, and Langfang Region, China

Abstract

PM _2.5 samples from Beijing, Tianjin, and Langfang were simultaneously collected from 20 November 2016 to 25 December 2016, and the organic carbon (OC) and elemental carbon (EC) content in the samples were measured and analyzed. The pollution characteristics and sources of OC and EC in atmospheric PM _2.5 for three adjacent cities were discussed. The average mass concentrations of OC in PM _2.5 in Beijing, Tianjin, and Langfang were 27.93 ± 23.35 μg/m ³, 25.27 ± 12.43 μg/m ³, and 52.75 ± 37.97 μg/m ³, respectively, and the mean mass concentrations of EC were 6.61 ± 5.13 μg/m ³, 6.14 ± 2.84 μg/m ³, and 12.06 ± 6.81 μg/m ³, respectively. The average mass concentration of total carbon (TC) accounted for 30.5%, 24.8%, and 49% of the average mass concentration of PM _2.5 in the atmosphere. The total carbonaceous matter (TCA) in Beijing, Tianjin, and Langfang was 51.29, 46.57, and 96.45 μg/m ³, respectively. The TCA was the main component of PM _2.5 in the region. The correlation between OC and EC in the three cities showed R ² values of 0.882, 0.633, and 0.784 for Beijing, Tianjin, and Langfang, respectively, indicating that the sources of urban carbonaceous aerosols had good consistency and stability. The OC/EC values of the three sampling points were 4.48 ± 1.45, 4.42 ± 1.77, and 4.22 ± 1.29, respectively, considerably greater than 2, indicating that the main sources of pollution were automobile exhaust, and the combustion of coal and biomass. The OC/EC minimum ratio method was used to estimate the secondary organic carbon (SOC) content in Beijing, Tianjin and Langfang. Their values were 10.73, 10.71, and 19.51, respectively, which accounted for 38%, 42%, and 37% of the average OC concentration in each city, respectively. The analysis of the eight carbon components showed that the main sources of pollutants in Beijing, Tianjin, and Langfang were exhaust emissions from gasoline vehicles, but the combustion of coal and biomass was relatively low. The pollution of road dust was more serious in Tianjin than in Beijing and Langfang. The contribution of biomass burning and coal-burning pollution sources to atmospheric carbon aerosols in Langfang was more prominent than that of Beijing and Tianjin.