Characteristics, sources and evolution processes of atmospheric organic aerosols at a roadside site in Hong Kong

摘要

A sampling campaign was conducted at an urban roadside site in Hong Kong from Nov. to Dec. in 2017 using a suite of state-of-the-art instruments to monitor compositions of non-refractory sub-micron particulate matter (NR-PM1) and gaseous pollutants. Results showed that the average NR-PM1 concentration was 26.1 +/- 0.7 mu g/m(3) (average +/- 95% confidence interval) and organic aerosol (OA) contributed the most to NR-PM1 with a proportion of 57.7 +/- 0.2%. The aerosol size distributions of bulk composition of NR-PM1 presented a peak at similar to 600 nm with internal mixtures of the organic and inorganic components, while there were a larger proportion of primary organic particles at 200 nm, indicating intensive emissions of primary organics at this site. Positive matrix factorization (PMF) analysis was applied to the measurement data and four OA components were identified, including a hydrocarbon-like OA (HOA) factor, a cooking organic aerosol (COA) factor and two oxygenated OA (OOA) factors of different oxidation levels: less oxidized OOA (LO-OOA) and more oxidized OOA (MO-OOA). Strikingly, the contribution of MO-OOA was the highest (30.9 +/- 0.4%), suggesting high oxidation degree and/or high regional background in the roadside environment. Moreover, the proportion of COA reached 25.4 +/- 0.3% at this roadside site with heavy traffic fleet, which was even higher than the percentage of HOA (p 0.01). The average ratio of C3H3O+ / C3H5O+ (2.01 +/- 0.01) and the opposite pattern of C3H3O+/C3H5O+ to O-x during daytime hours suggested that the COA was oxidized to some extent when transported to the site. The findings implied that cooking activities are a significant source of organic aerosols in Hong Kong, even at a busy road. Control measures should focus on both cooking and traffic emissions in Hong Kong.