Variation of Modified Combustion Efficiency and Its Impact on Biomass Burning Emission Estimation in Africa

Abstract

Biomass burning (BB) is one of the largest sources of trace gases and primary carbonaceous particles in the global troposphere, posing great impacts on air quality and regional climate. Accurate quantification of BB emissions is vital for assessing its environmental and climate impacts. However, there are still large uncertainties in current BB emission inventories due to poorly characterized emission rates under different combustion states. The fixed emission factor (EF) instead of varying EF associated with different combustion efficiencies may be the reason for the bias. Here, based on satellite-retrieved carbon dioxide (CO₂) and carbon monoxide (CO), the modified combustion efficiency (MCE) is derived for fire-prone regions in Africa. The monthly and inter-annual variability of MCE shows a good correlation with meteorological variables such as relative humidity. Therefore, variable EF was established based on its statistical relationship with MCE for different fire-emitted species. Application of such MCE-dependent EF in the global climate-chemistry model can greatly improve the performance of wildfire smoke pollution during the fire season, indicated by an increase of 31% in aerosol optical depth (AOD) and a 50% reduction in normalized mean bias compared with AOD observations. The study elucidates the critical role of meteorology in BB emission estimates and highlights the importance of implementing a dynamic fire emission inventory in response to meteorological conditions.