Impacts of Pyrocb Injection Amount and Height on Model-Simulated Aerosol Optical Properties and Radiative Forcing after the Australian New Year Super Outbreak

Intense pyroCb activities directly inject gases and particles into the stratosphere. The long-lived pyroCb plume alters incoming solar radiation and results in substantial impacts on climate. Previous studies showed that there are a large amount of uncertainties of pyroCb injection amount and height. Therefore, it is necessary to investigate how these uncertainties affect aerosol optical properties and the relevant aerosol radiative forcing (ARF). In this study, we used the chemistry transport model GEOS-Chem incorporated with sectional advanced particle microphysics (APM) module (GCAPM) to simulate the evolution of pyroCb plume after the Australian New Year Super Outbreak (ANYSO). A three dimensional emission inventory was created with ~0.7 Tg stratospheric smoke mass estimated from top-down method in Peterson et al., 2021 considering the injection height observed by CALIOP. GCAPM simulated daily aerosol extinction at 700 nm (AEC_700) was compared with daily aerosol extinction at 675 nm (AEC_675) retrieved by OMPS-LP from 12/01/2019 to 06/30/2020. The comparison indicated that GCAPM simulation significantly underestimated aerosol extinction retrieved by OMPS-LP when using the default ANYSO emission. After applying the scaling factor gained by the top-down estimation of aerosol extinction in January to black carbon and organic carbon emitted by ANYSO, GCAPM simulated AEC_700 was enhanced by a factor of ~2 and was closer the OMPS-LP retrieved AEC_675. The comparison between model simulation and satellite retrieval also indicated that the high values of AEC_700 simulated by GCAPM were located at 12–16 km, while the high values of AEC_675 retrieved by OMPS-LP were located at 8–12 km. The sensitive study of new injection height (NIH) indicated that NIH extended the lifetime of aerosol at the high altitude (14–18 km). The simulation that uses NIH and scaling factor showed better agreement with OMPS-LP retrievals than the other 3 cases. The analysis of the spatial distributions and temporal variations of model simulation and satellite retrieval also indicated that the difference of peak times of GCAPM simulated AEC_700 and OMPS-LP retrieved AEC_675 may be caused by the heterogeneous distribution of plumes in the early period of ANYSO. Due to limitations in the geographical sampling of OMPS-LP, the high values of aerosol extinction represent by GCAPM with coarse grids may be missed in OMPS-LP retrievals. Our study also found that the changes of ARF due to different injection amount and height assumptions are comparable to the ARF caused by the default injection assumption. The impacts of different aerosol schemes (e.g. bulk aerosol and sectional aerosol) and initial size distribution assumptions will be discussed.