Variabilities in PM2.5 and Black Carbon Surface Concentrations Reproduced by Aerosol Optical Properties Estimated by In-Situ Data, Ground Based Remote Sensing and Modeling

Abstract

Because of the increased temporal and spatial resolutions of the sensors onboard recently launched satellites, satellite-based surface aerosol concentration, which is usually estimated from the aerosol optical depth (AOD), is expected to become a strategic tool for air quality studies in the future. By further exploring the relationships of aerosol concentrations and their optical properties using ground observations, the accuracies of these products can be improved. Here, we analyzed collocated observations of surface mass concentrations of fine particulate matter (PM2.5) and black carbon (BC), as well as columnar aerosol optical properties from a sky radiometer and aerosol extinction profiles obtained by multi-axis differential optical absorption spectroscopy (MAX-DOAS), during the 2019–2020 period. We focused the analyses on a daily scale, emphasizing the role of the ultraviolet (UV) spectral region. Generally, the correlation between the AOD of the fine fraction (i.e., fAOD) and the PM2.5 surface concentration was moderately strong, regardless of considerations of boundary layer humidity and altitude. In contrast, the fAOD of the partial column below 1 km, which was obtained by combining sky radiometer and MAX-DOAS retrievals, better reproduced the variability of the PM2.5 and resulted in a linear relationship. In the same manner, we demonstrated that the absorption AOD of the fine fraction (fAAOD) of the partial column was related to the variability of the BC concentration. Analogous analyses based on aerosol products from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) confirmed these findings and highlighted the importance of the shape of the aerosol profile. Overall, our results indicated a remarkable consistency among the retrieved datasets, and between the datasets and MERRA-2 products. These results confirmed the well-known sensitivity to aerosol absorption in the UV spectral region; they also highlighted the efficacy of combined MAX-DOAS and sky radiometer observations.

Comment on acp-2022-110

“…Therefore, as CAMS simulations did not include the Finally, we considered the changes in light-absorbing aerosol in both the boundary layer and the total column. Although this dataset is characterized by high uncertainty (Damiani et al, 2021), the values in 2020 were clearly the lowest on record. The largest relative changes (not shown) occurred before the state of emergency (i.e., in January and February), while the largest absolute change occurred in fall; nonetheless, some reduction was apparent in May.…”

“…Light-absorbing aerosols within the boundary layer were estimated to be described in Damiani et al (2021), combining sky radiometer and MAX-DOAS optical property data at UV wavelengths. Then, in the following analysis, we examine the finemode absorbing AOD within the partial column below 1 km (i.e., fAAOD [0-1 km]), which was computed by combining the columnar fine-mode fraction (FMF) and single scattering albedo (SSA) parameters retrieved from the sky radiometer with the mean partial column AOD estimated from MAX-DOAS measurements.…”

“…Finally, we combined optical property information retrieved by a sky radiometer with MAX-DOAS data to estimate lightabsorbing aerosols within the boundary layer (Damiani et al, 2021), as described in Section 2.2.…”

“…In this huge urbanized region, lightabsorbing aerosols tend to be produced mainly by local pollution. However, transboundary transport has been shown to further modulate the light-absorbing aerosol dataset (Damiani et al, 2021), complicating the attribution of effects to the pandemic.…”