Impacts of biomass burning on tropospheric CO, NOx, and O-3

This study utilizes the National Oceanic and Atmospheric Administration Geo physical Fluid Dynamics Laboratory three-dimensional global chemical transp ort model to quantify the impacts of biomass burning on tropospheric concen trations of carbon monoxide (CO), nitrogen oxides (NOx), and ozone (O-3). W e construct updated global sources that emit 748 Tg CO/yr and 7.8 Tg N/yr i n the surface layer. Both sources include six types of biomass: forest, sav anna, fuelwood, agricultural residues, domestic crop residues (burned in th e home for cooking and/or heating), and dried animal waste. Timing for the burning of forest, savanna, and agricultural residues is based upon regiona l cultural use of fire, vegetation type, local climate, and information gat hered from satellite observations, while emissions from the burning of fuel wood, domestic crop residues, and dried animal waste are constant throughou t the year. Based on agreement with observations, particularly of CO, we co nclude that the collective uncertainty in our biomass burning sources is mu ch less than the factor of two suggested by previous estimates of biomass b urned in the tropics annually. Overall, biomass burning is a major source o f CO and NOx in the northern high latitudes during the summer and fall and in the tropics throughout most of the year. While it contributes more than 50% of both the NOx and CO in the boundary layer over major source regions, it has a much larger global impact on the CO-distribution in comparison to either NOx or O-3, contributing 15 to 30% of the entire tropospheric CO ba ckground. The only significant biomass burning contribution to NOx at 500 m bar, due to the short lifetime of NOx in the lower troposphere, is a plume occurring July through October in the Southern Hemisphere subtropical free troposphere, stretching from South America to the western Pacific. The larg est impacts on O-3 are limited to those regions where NOx impacts are large as well. Near the surface, biomass burning indirectly contributes less tha n half of the total O-3 concentrations over major tropical source regions, up to 15% throughout the year in the tropics, and 10 to 20% throughout the Southern Hemisphere during September through November. At 500 mbar, the lar gest contribution to O-3 (20 - 30%) is correlated with the NOx plume during July through November. Biomass burning contributes less than 15% of either NOx or O-3 in the upper troposphere.