Chemical Characterization of Primary Water-Soluble Organic Gas Emissions from African Biomass Burning

Wildfires and other biomass burning (BB) events emit substantial amounts of water-soluble organic (WSO) gases into the atmosphere, where they can subsequently partition into cloud and aerosol water. Native African plant material has been grossly understudied compared to other geographic regions despite accounting for nearly half of the worldwide BB emissions. This study characterized primary WSO gas emissions from laboratory burns of eight native African biomass fuels (acacia, wanza, mukusi, mosetlha, mopane, savannah grass, mokala, and olive) under smoldering conditions. WSO gases were collected using mist chambers and analyzed by reversed-phase liquid chromatography coupled to a high-resolution quadrupole time-of-flight mass spectrometer. Acacia, mukusi, mokala, and grass exhibited the largest primary gaseous WSO carbon emission factors, and wanza showed the smallest. We determined the dependence of both NOx and WSO gas emissions on biomass fuel under identical combustion conditions. While only modest variations in relative concentrations of CxHyOz compounds were observed between other fuels, wanza exhibited high relative concentrations of CxHyOzN compounds and NO2/NOx, suggesting that its combustion yields nitroaromatics, making it likely a poor choice for indoor heating and cooking purposes. A total of 31 unique molecules are discussed along with their potential implications for aqueous secondary organic aerosol (aqSOA).