Aircraft observations of aerosols and BC in autumn over Guangxi Province, China: Diurnal variation, vertical distribution and source appointment

Abstract

To understand the vertical distribution characteristics of aerosols and black carbon (BC) in southwest China, 12 sorties were conducted from October 10 to November 3, 2020, and the vertical profiles of aerosols and BC at different times in Nanning, Guangxi Province, in autumn were obtained. The contents of aerosols (Na <100 cm−3) and BC (MBC <0.11 μg∙m−3) at 2000–6000 m were small and did not change with height. The vertical profiles of Na and MBC below 2000 m were affected by the boundary layer (PBL), and the vertical profiles had obvious diurnal variations. Aerosols and BC in the residual layer (RL) entered PBL at 10:00–12:00, resulting in increased the values of Na (1971 cm−3) and MBC (2.93 μg∙m−3) in PBL. Under intense turbulent activity in PBL from 13:00 to 15:00, Na and MBC changed little with height. At 17:00, PBL height dropped, aerosols and BC remained in RL. From 18:00 to 22:00, the PBL height decreased, and the aerosols and BC were trapped below 200 m. BC below 2000 m was mainly from fossil fuel combustion. Between 2000 m and 6000 m, MBCff > MBCbb at 12:00–17:00, and MBCbb was similar to MBCff at 10:00, 18:00 and 22:00. The air masses passing over Southeast Asian countries and Guangdong Province brought more BC to Guangxi Province. Air masses from different sources had different effects on aerosols in Guangxi Province. Below 3000 m, the value of Na under the influence of land air mass was greater than that under the influence of ocean air mass. Above 3000 m, different sources of air mass mainly affected the aerosol number concentration spectrum. Under the influence of ocean air mass, the number and concentration of aerosol with particle size of 0.11 μm and 0.24 μm had increased in Guangxi Province.