An Examination of the Effects of Aerosol ChemicalComposition and Size on Radiative Properties of Multi-Component Aerosols

The sensitivity of aerosol radiative properties (i.e., scattering coefficient, extinction coefficient, single scatter albedo, and asymmetry factor) and radiation transmission to aerosol composition, size distributions, and relative humidity (RH) is examined in this paper. Mie calculations and radiation calculations using a tropospheric visible radiation model are performed. The aerosol systems considered include inorganic and organic ions (e.g., Cl-, Br-, , , Na+, , K+, Ca2+, Mg2+, HCOO-, CH3COO-, CH3CH2COO-, CH3COCOO-, OOCCOO2-, MSA1-), and (2) water-insoluble inorganic and organic compounds e.g., (black carbon, n-alkanes, SiO2, Al2O3, Fe2O3 and other organic compounds). The partial molar refraction method and the volume-average method are used to calculate the real and imaginary parts of refractive index of real aerosols, respectively. The sensitivity simulations show that extinction coefficient increases by 70% when RH varies from 0 to 80%. Both extinction coefficient and asymmetry factor increase by ~48% when real part varies from 1.40 to 1.65. Scattering coefficient and single scattering albedo decrease by 18% and 24%, respectively, when the imaginary part varies from –0.005 to –0.1. Scattering and extinction coefficients increase by factors of 118 and 123, respectively, when the geometric mean radius varies from 0.05 to 0.3 ?m. Scattering and extinction coefficients and asymmetry factor increase by factors of 389, 334, and 5.4, respectively, when geometric standard deviation varies from 1.2 to 3.0. The sensitivity simulations using a tropospheric visible radiation model show that the radiation transmission is very sensitive to the change in geometric mean radius and standard deviation;other factors are insignificant.

Large contributions of emission reductions and meteorological conditions to the abatement of PM_(2.5)in Beijing during the 24th Winter Olympic Games in 2022

To guarantee the blue skies for the 2022 Winter Olympics held in Beijing and Zhangjiakou from February 4 to 20,Beijing and its surrounding areas adopted a series of emission control measures.This provides an opportunity to determine the impacts of large-scale temporary control measures on the air quality in Beijing during this special period.Here,we applied the WRF-CMAQ model to quantify the contributions of emission reduction measures and meteorological conditions.Results show that meteorological conditions in 2022 decreased PM_(2.5)in Beijing by 6.9 and 11.8μg/m^(3)relative to 2021 under the scenarios with and without emission reductions,respectively.Strict emission reduction measures implemented in Beijing and seven neighboring provinces resulted in an average decrease of 13.0μg/m^(3)(-41.2%)in PM_(2.5)in Beijing.Over the entire period,local emission reductions contributed more to good air quality in Beijing than nonlocal emission reductions.Under the emission reduction scenario,local,controlled regions,other regions,and boundary conditions contributed 47.7%,42.0%,5.3%,and 5.0%to the PM_(2.5)concentrations in Beijing,respectively.The results indicate that during the cleaning period with the air masses from the northwest,the abatements of PM_(2.5)were mainly caused by local emission reductions.However,during the potential pollution period with the air masses from the east-northeast and west-southwest,the abatements of PM_(2.5)were caused by both local and nonlocal emission reductions almost equally.This implies that regional coordinated prevention and control strategies need to be arranged scientifically and rationally when heavy pollution events are forecasted.