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

Simulations of biomass burning (BB) emissions in chemistry transport models strongly depend on the inventories that define emission source location and strength. We use 13 global biomass burning emission estimates, including the widely used Global Fire Emission Database (GFED) monthly and daily versions, Fire Radiative Power (FRP)-based Quick Fire Emission Data set QFED, and 11 calculated emissions from different combinations of burned area based on the Moderate Resolution Imaging Spectroradiometer (MODIS) products, effective fuel load, and species emission factors as alternative inputs to the global Goddard Chemistry Aerosol Radiation and Transport (GOCART) model. The resultant simulated aerosol optical depth (AOD) and its spatial distribution are compared to AOD snapshots measured by the MODIS instrument for 124 fire events occurring between 2006 and 2007. This comparison exposes the regional biases of each emission option. GOCART average fire AOD values compare best to MODIS-measured AOD when the daily GFED inventory is used as input to GOCART. Even though GFED-based emission options provide the lowest emissions in the tropics, GFED-based GOCART AOD compares best with MODIS AOD in tropical cases. Fire-counts-based emission options give the largest emission estimates in the boreal regions, and the model performs best at higher latitudes with these inputs when compared to MODIS. Comparison of total annual BB emissions by all inventories suggests that burned area estimates are usually the largest source of disagreement. It is also shown that the quantitative relationship between BB aerosol emission rate and model-simulated AOD is related to the horizontal plume dispersion, which can be approximated by the wind speed in the planetary boundary layer in most cases. Thus, given average wind speed of the smoke plume environment, MODIS-measured AOD can provide a constraint to the strength of BB sources at the level of individual plumes.