Abstract
Aerosol particles can strongly affect both air quality and the radiation budget of the atmosphere. Above Beijing, the capital city of China, large amounts of aerosols within the atmospheric column have caused the deterioration of local air quality and have influenced radiative forcings at both the top and the bottom of the atmosphere (BOA and TOA). Observations of aerosol radiative forcing and its efficiency have been made using two sun-photometers in urban Beijing between 2013 and 2015, and have been analyzed alongside two air quality monitoring stations’ data by dividing air quality conditions into unpolluted, moderately polluted, and heavily polluted days. Daily average PM2.5 concentrations varied greatly in urban Beijing (5.5–485.0 µg/m3) and more than one-third of the analyzed period is classified as being polluted according to the national ambient air quality standards of China. The heavily polluted days had the largest bottom of atmosphere (BOA) and top of atmosphere (TOA) radiative forcings, but the smallest radiative forcing efficiencies, while the unpolluted days showed the opposite characteristics. On heavily polluted days, the averaged BOA aerosol radiative forcing occasionally exceeded −150 W/m2, which represents a value about three-times greater than that for unpolluted days. BOA aerosol radiative forcing was around two-to-three times as large as TOA aerosol radiative forcing under various air quality conditions, although both were mostly negative, suggesting that aerosols had different magnitudes of cooling effects at both the surface and the top of the atmosphere. Unpolluted days had the largest average values of aerosol radiative forcing efficiencies at BOA (and TOA) levels, which exceeded −190 W/m2 (−70 W/m2), compared with the lowest average values in heavily polluted days of around −120 W/m2 (−55 W/m2). These results suggest that the high concentrations of particulate matter pollution in the urban Beijing area had a strong cooling effect at both BOA and TOA levels.
Highlights
Aerosols can strongly influence the earth’s energy budget by scattering and absorbing solar radiation [1,2]
Inversions of data obtained from ground-based aerosol observation networks—especially Aerosol Robotic Network (AERONET)—provide a unique and reliable data source that can be used to examine the effects of radiative forcing under different aerosol loading conditions [11,12]
Due to the accuracy of aerosol properties retrieved by this system, AERONET measurements are regarded as an important benchmark for the validation of various satellite aerosol retrievals [25], and are commonly used to calculate radiative forcing [26]
Summary
Aerosols can strongly influence the earth’s energy budget by scattering and absorbing solar radiation [1,2]. Aerosol particles within an atmospheric column may alter the radiative balance at its Remote Sens. Aerosols can impact the radiative balance of the atmosphere by influencing the microphysical properties of clouds [6]. Variations in the microphysical properties of these particles (e.g., size distribution, single scattering albedo, and refractive indices) may play important roles in radiative forcing. Can provide detailed information about the optical and microphysical properties of aerosols, as well as radiative forcing through utilizing the direct and scattering measurements [7,8,9]. Inversions of data obtained from ground-based aerosol observation networks—especially AERONET—provide a unique and reliable data source that can be used to examine the effects of radiative forcing under different aerosol loading conditions [11,12]
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