Aerosol Optical Properties in Summer in Typical Urban Area of Beijing: Variations, Potential Sources, and Influence on Ground-Level-Ozone Formation Mechanism

Atmospheric aerosols directly or indirectly affect the concentrations of other atmospheric components (e.g., ozone) through radiative effects and their surface chemistry, therefore studies on the optical and radiative properties of aerosols could provide effective information for atmospheric environmental pollution control. In this study, key optical parameters of aerosols and comprehensive observation of atmospheric photochemistry in urban areas of Beijing were carried out in summer in 2019 to investigate the aerosol optical properties, potential sources, and their effects on ozone photochemical formation mechanisms in the typical urban area of Beijing. The results showed that the aerosols in the urban area of Beijing had strong scattering properties in summer, and the classification of aerosols showed that moderately scattering fine-mode aerosols (24.58%) accounted for the largest percentage. High relative humidity (RH) environment further enhanced the scattering ability of scattering aerosols, but had no such effect on the absorbing aerosols. The contribution of regional transport to PM 2.5 was more significant than that of local sources in Beijing, which was mainly influenced by Hebei, Tianjin and Shandong, where the aerosols from this region were mainly fine-modal and had a strong scattering ability. The simulation results of NCAR MM indicated that the total incremental effect of ozone precursors and atmospheric aerosols on ozone formation was 6.26 ppbv for haze pollution episodes compared to clean days during the observation period. Single scattering albedo (SSA) and aerosol optical depth (AOD) were the dominant factors affecting ozone growth or reduction with the low concentration of nitrogen oxides (NO x ) and volatile organic compounds (VOCs), the mean contribution of extinction from SSA and AOD to ozone concentration increment were 11.25 and –3.94 ppbv, respectively. The results of this study could provide some reference for the development of synergistic PM 2.5 and ozone pollution prevention and control strategies.