Indirect contributions of global fires to surface ozone through ozone-vegetation feedback

Fire is an important source of surface ozone (O3), which causes damage to vegetation and reduces stomatal conductance. Such processes can feed back to inhibit dry deposition and indirectly enhance surface O3. Here, we apply a fully coupled chemistry-vegetation model to estimate the indirect contributions of global fires to surface O3 through O3-vegetation feedback during 2005–2012. Fire emissions directly increase the global mean annual O3 by 1.2 ppbv (5.0 %) with a maximum of 5.9 ppbv (24.4 %) averaged over central Africa by emitting substantial number of precursors. Considering O3-vegetation feedback, fires additionally increase surface O3 by 0.5 ppbv averaged over the Amazon in October, 0.3 ppbv averaged over southern Asia in April, and 0.2 ppbv averaged over central Africa in April. During extreme O3-vegetation interactions, such feedback can rise to > 0.6 ppbv in these fire-prone areas. Moreover, large ratios of indirect-to-direct fire O3 are found in eastern China (3.7 %) and the eastern U.S. (2.0 %), where the high ambient O3 causes strong O3-vegetation interactions. With likelihood of increasing fire risks in a warming climate, fires may promote surface O3 through both direct emissions and indirect chemistry-vegetation feedbacks. Such indirect enhancement will cause additional threats to public health and ecosystem productivity.