资源环境科技发展态势分析平台

Aerosol optical properties are important indices for monitoring atmospheric aerosol pollution. In this study, we report the seasonal and diurnal variability of major aerosol optical parameters, including scattering coefficient (σ_s), absorbing coefficient (σ_a), single scattering albedo (SSA), together with PM_2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) and PM₁₀ (particulate matter with aerodynamic diameter ≤ 10 μm) mass concentrations measured at an urban site in Beijing from September 2017 to August 2019. The relationships between these aerosol properties with meteorological conditions, in particular, the mixing layer height (MLH), wind speed, and wind direction, are further investigated. Results show that the annual average values of PM_2.5 and PM₁₀ mass concentrations, σ_s, and σ_a during the study period are 54 ± 54 μg/m³, 100 ± 72 μg/m³, 170 ± 180 Mm⁻¹, 17 ± 15 Mm⁻¹ respectively, which are much lower than those previously reported, indicating the effectiveness of strict pollution control strategies implemented in recent years. SSA is calculated with σ_s and σ_a, whose annual average value is 0.88 ± 0.07. Seasonally, σ_a exhibits dual peaks except in summer, PM_2.5 and PM₁₀ concentrations are the highest value in the spring, whereas σ_s has the highest value in the summer with a secondary peak in the spring. The diurnal cycle of σ_a is highly anti-correlated with that of the MLH. For σ_s, PM_2.5 and PM₁₀, their diurnal cycles often peak around noon and are in phase with the MLH in the spring and summer, which may be associated with the photochemical production of secondary aerosols. σ_s, σ_a, PM₁₀, and PM_2.5 concentrations are inversely related to wind speed, but PM₁₀ starts to increase as wind speed exceeds 4 m/s, possibly caused by dust and catkins. The increase in wind speed also weakens the aerosol-MLH relationship. Back trajectory analysis indicates that high aerosol concentrations are mostly associated with southward and westward airmasses.