Seasonal variations of mass absorption efficiency of elemental carbon in PM2.5 in urban Guangzhou of South China

Abstract

This study investigates seasonal variations of mass absorption efficiency of elemental carbon (MAE_EC) and possible influencing factors in urban Guangzhou of south China. Mass concentrations of elemental carbon (EC) and organic carbon (OC) in PM_2.5 and aerosol absorption coefficient (b_ap) at multi-wavelengths were simultaneously measured in four seasons of 2018–2019 at hourly resolution by a semi-continuous carbon analyzer and an aethalometer. Seasonal average mass concentrations of EC were in the range of 1.36–1.70 μgC/m³ with a lower value in summer than in the other seasons, while those of OC were in the range of 4.70–6.49 μgC/m³ with the lowest value in summer and the highest in autumn. Vehicle exhaust from local traffic was identified to be the predominant source of carbonaceous aerosols. The average aerosol absorption Ångström exponents (AAE) were lower than 1.2 in four seasons, indicating EC and b_ap were closely related with vehicle exhaust. Seasonal MAE_EC at 550 nm was 11.0, 8.5, 10.4 and 11.3 m2/g in spring, summer, autumn, and winter, respectively. High MAE_EC was related with the high mass ratio of non-carbonaceous aerosols to EC and high ambient relative humidity.