A Physically Based PM$_{\text{2.5}}$ Estimation Method Using AERONET Data in Beijing Area

Over the past few years, regional air pollution has frequently occurred in Mid-Eastern China, especially in Beijing. As the primary pollutant in urban air, atmospheric particulate matter (PM) not only leads to the decrease of atmospheric visibility, but also increases the mortality and morbidity of respiratory system diseases. By analyzing aerosol volume size distribution data downloaded from the AERONET official website, we find that the size distribution of aerosol in Beijing appears a bimodal log-normal structures and parameters of fine mode in AERONET data are mainly contributed by PM<inline-formula><tex-math notation="LaTeX">$_{\text{2.5}}$</tex-math></inline-formula>. In this paper, a physically based model is developed to estimate the concentration of PM<inline-formula> <tex-math notation="LaTeX">$_{\text{2.5}}$</tex-math></inline-formula>, in which, fine mode aerosol optical depth (AOD) at 440, 550, and 675 nm, Effective Radius of the Fine particles, ground-based fine particulate matter (PM <inline-formula><tex-math notation="LaTeX">$_{\text{2.5}}$</tex-math></inline-formula>) data, relative humidity, and boundary layer height data from 2015 to 2016 are used. Those from 2015 are used for calculating integrated extinction efficiencies (〈<italic>Qext</italic>〉) based on the model, and those from 2016 are used for PM <inline-formula><tex-math notation="LaTeX">$_{\text{2.5}}$</tex-math></inline-formula> validation. Result shows that R ² of retrieved PM<inline-formula><tex-math notation="LaTeX">$_{\text{2.5}}$</tex-math></inline-formula> against ground-based PM<inline-formula><tex-math notation="LaTeX">$_{\text{2.5}}$</tex-math></inline-formula> can reach to 0.70 and RMSE is 33.67 μg/m³ at Beijing site at 440 nm. This study concludes that this method has the potential to retrieve PM<inline-formula><tex-math notation="LaTeX">$_{\text{2.5}}$</tex-math> </inline-formula> by using AERONET AOD in Beijing, which is independent of ground-based PM<inline-formula> <tex-math notation="LaTeX">$_{\text{2.5}}$</tex-math></inline-formula> measurement.