Characteristics of Carbonaceous Species in PM2.5 in Chengdu Under the Background of Emission Reduction

Abstract

The Air Pollution Prevention and Control Action Plan and Three-year Plan on Defending the Blue Sky promulgated by the State Council of the People's Republic of China have played an important role in the overall improvement of air quality in China. However, few studies have evaluated the implementation effects of these two policies in Sichuan Basin and the new characteristics of PM2.5 chemical components after the implementation of these policies. The key periods for evaluating the implementation effects of these two pollution reduction policies are 2017 and 2020, respectively. In order to study the atmospheric PM2.5 and carbonaceous species in Chengdu during these two periods, this study sampled the PM2.5 in Chengdu from October 2016 to July 2017 and December 2020, respectively, and the organic carbon (OC) and elemental carbon (EC) were analyzed. The results showed that the annual ρ(PM2.5) from 2016-2017 in Chengdu was (114.0±76.4) μg·m-3. The maximum value of the ρ(PM2.5) appeared in winter[(193.3±98.5) μg·m-3], and the minimum value appeared in spring[(73.8±32.3) μg·m-3]. By contrast, the ρ(PM2.5) in winter decreased significantly in 2020, with a value of (96.0±39.3) μg·m-3. The annual ρ(OC) and ρ(EC) from 2016-2017 were (21.1±16.4) μg·m-3 and (1.9±1.3) μg·m-3, which accounted for 18.5% and 1.7% of the PM2.5 mass, respectively. The seasonal variation characteristic of ρ(OC) was:winter[(40.6±21.5) μg·m-3]>autumn[(17.0±7.0) μg·m-3]>summer[(14.4±3.9) μg·m-3]>spring[(12.6±6.0) μg·m-3], whereas the ρ(EC) in the four seasons were close, ranging from 1.3 to 2.4 μg·m-3. The annual ρ(SOC) was (9.4±9.1) μg·m-3, which accounted for 44.5% of the OC mass. Compared with that in winter 2016, the ρ(OC) decreased by 52.7% in winter 2020, whereas the ρ(EC) increased by 26.1%. With the aggravation of pollution, the change trends of carbon species and their contributions were different. Compared with that in winter 2016, the variation in the contribution of OC with the aggravation of pollution in winter 2020 was more stable, whereas the proportion of SOC increased more obviously. There were obvious differences in the direction of air masses and the potential source area of pollutants in each season. Although there was no significant change in the direction of air masses in winter 2020 compared with those in winter 2016, the pollutant concentrations corresponding to each cluster decreased significantly, and the potential source area of pollutants expanded significantly to the eastern area.