Aerosol optical properties observed during Campaign of Air QualityResearch in Beijing 2006 (CAREBeijing-2006): Characteristicdifferences between the inflow and outflow of Beijing city air

摘要

Ground-based measurements of aerosol optical properties were conducted duringCampaign of Air Quality Research in Beijing 2006 (CAREBeijing-2006) (11 August to9 September 2006) at a suburban site ~30 km south of Beijing. Averaged over themeasurement campaign (arithmetic mean ± standard deviation), the total scatteringcoefficients (σ_s) were 469 374 Mm~(-1)(450 nm), 361 ± 295 Mm~(-1)(550 nm), and 249 ±206 Mm~(-1)(700 nm) and the absorption coefficient (σ_a) was 51.8 ± 36.5 Mm~(-1)(532 nm).The average Angstrom exponent was 1.42 ± 0.19 (450 nm/700 nm) and the average singlescattering albedo (w532) was 0.86 ± 0.07 (532 nm) with minimum values as low as 0.5.Pronounced diurnal cycles were observed inσ_s, σ_a, and ω_(532)and can be explained byboundary layer mixing effects. Additionally, an enhancement of absorbing particles in theearly morning (0500-0800 local time) was observed; this may be attributed to sootemissions from traffic activity. When the measured air masses originated in the north andpassed over Beijing, the single scattering albedo was generally low (w532 < 0.8), whichindicates that the local emissions of particulate matter in Beijing were dominated byprimary particles from combustion sources (soot). The southerly inflow to Beijing hadtypically very high σ_sand higher than average ω_(532)values, suggesting a large amount ofsecondary aerosol (e.g., sulfate and oxidized organics). Overall, the results suggest that amajority of the particle pollution in Beijing is transported into the city from the south.