The use of satellite-measured aerosol optical depth to constrain biomass burning emissions source strength in a global model GOCART

Biomass burning (BB) is one of the major contributors to emissions of carbonaceous atmospheric aerosol. Optically and chemically potent BB particles play important roles in atmospheric processes through their impact on air quality, visibility, human health, and as one of the factors affecting global climate through direct and indirect radiative effects. As chemistry transport models are among the major tools for studying earth and atmospheric processes, it is important to represent BB processes as accurately as possible. Simulations of BB emissions in aerosol models strongly depend on the inventories that define emission source locations and strength. In this work, we use 13 global biomass burning emission estimates, including widely used Global Fire Emission Database (GFED) monthly and daily versions, Fire Radiative Power (FRP)-based Quick Fire Emission Dataset QFED, and several combinations of fuel consumption estimates, aerosol emission factors and Moderate Resolution Imaging Spectroradiometer (MODIS)-based burned area products as alternative inputs to the global Goddard Chemistry Aerosol Radiation and Transport (GOCART) model. The resultant simulated aerosol optical depth (AOD) and its spatial distributions are compared to AOD snapshots measured by the MODIS instrument for 124 fire events occurring between 2006 and 2007. BB aerosol emission estimates by all 13 emission options are compared on a global scale and implications of regional differences are discussed. Performance of all emission options, with the exception of FRP-based QFED, when used as a source of BB emissions in the GOCART model, were assessed on a regional basis, showing where and to what degree the different options overestimate, underestimate and provide good agreement with the observation. QFED developers use MODIS AOD as one of the parameters to calibrate their product during its production, so comparison of QFED-based GOCART-simulated AOD with MODIS measurements was not performed. It is also shown that the quantitative relationship between BB aerosol emissions and model-simulated AOD is related to the horizontal plume dispersion, which can be approximated by the wind speed in the planetary boundary layer. Thus, given average wind speed of the smoke plume environment, MODIS-measured AOD can provide a constraint to the strength of BB sources