Impact of PM_(2.5) chemical compositions on aerosol light scattering in Guangzhou - the largest megacity in South China

摘要

Daily PM_(2.5) samples were collected in Guangzhou - the largest megacity in South China, for a period of one month in each season during 2009-2010. Mass concentrations of water-soluble inorganic ions, organic carbon (OC) and elemental carbon (EC) in PM_(2.5) were determined, and aerosol scattering coefficient (b_(sp)) was synchronously measured. The daily PM_(2.5) mass concentrations ranged from 21.0 to 213.6 ug m~3 with an annual average of 76.8 ± 41.5 μg m~(-3). The highest seasonal average PM_(2.5) was observed in winter (103.3 ± 50.1 μg m~(-3)) and the lowest in summer (38.6 ± 15.7 μg m~(-3)). Annual average PM2.5 mass scattering efficiency (MSE) was 3.5 ± 0.9 m~2 g~(-1), with obvious seasonal variations in sequence of autumn (4.5 ± 0.2 m~2 g~(-1)) > winter (3.9 ± 0.5 m~2 g~(-1)) ＞ spring (3.0 ± 0.4 m~2 g~(-1)) > summer (23 ± 03 m~2 g~(-1)). To determine the relationship between b_(sp) and the chemical components of PM_(2.5) b_(sp) was reconstructed in each season using the original IMPROVE formula with a modification of including sea salt aerosols. The estimated b_(sp) using this method was 22 ± 28% smaller on annual average compared to the measurements. Multiple linear regression of measured b_(sp) against (NH_4)_2SO_4, NH_4NO_3, OM (Organic Mass). SS (Sea Salt). FS (Fine Soil), and CM (Coarse Mass) were also performed in all the four seasons. The estimated b_(sp) from using the regression equation was 4 ± 12% larger than the measured values. On average, (NH_4)_2SO_4, NR_4NO_3, OM, SS, FS and CM accounted for 50 ± 11%, 18 ± 10%, 19 ± 5%, 5 ± 4%, 3 ± 2% and 5 ± 6%, respectively, of the estimated b_(sp).