Long-term variations of aerosol optical properties over Wuhan with polarization lidar

Abstract

Aerosols greatly impact the global and regional climate system and public health. We conducted lidar measurements at Wuhan (30.53°N, 114.37°E) from October 2010 to June 2020 and analyzed the massive dataset with an automatic lidar processing algorithm, to investigate the long-term variations of aerosols. Lidar-derived total aerosol optical depth (AOD) at 532 nm shows an interannual decrease of −0.049 since 2010. Compared with AODs in other megacities worldwide, the AOD for Wuhan shows the largest decrease rate. After separating AOD contributions from boundary layer (BL) and free troposphere (FT), different evolution patterns are revealed with AOD decrease rates of −0.009 and −0.044 per year for FT and BL, respectively, which indicates more than 80% of AOD decrease are associated with reductions of local emissions. In addition, BL AOD was always larger than FT AOD before COVID-19 lockdown. However, this relation was conversed thereafter, with the lowest value of 0.125 for BL AOD since 2010, which is only the half of FT AOD within the same period. This feature corroborates strong influences of COVID-19 lockdown on human activities and local emissions. These findings can improve our understandings of regional aerosol responses to pollution controls and aerosol direct impacts on regional climate.