Abstract
Abstract. Fire is an important source of ozone (O3) precursors. The formation of surface O3 can cause damage to vegetation and reduce 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 annual mean O3 by 1.2 ppbv (5.0 %) with a maximum of 5.9 ppbv (24.4 %) averaged over central Africa by emitting a 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 a 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 US (2.0 %), where the high ambient O3 causes strong O3–vegetation interactions. With the 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.
Highlights
Tropospheric ozone (O3) is a toxic air pollutant with detrimental effects on vegetation (Yue and Unger, 2014; Juránet al., 2021)
We find that fire-induced O3 causes a positive feedback to surface [O3] mainly because of the inhibition effects on stomatal conductance
O3– vegetation feedback driven by fires enhances surface annual [O3] by 0.13 ppbv averaged over the Amazon, 0.12 ppbv averaged over central Africa, and 0.09 ppbv averaged over southern Asia
Summary
Tropospheric ozone (O3) is a toxic air pollutant with detrimental effects on vegetation (Yue and Unger, 2014; Juránet al., 2021). Modeling studies estimated that O3 damage reduces global GPP by 1.5 %–3.6 % with regional maximum reductions of 8 %– 20 % over eastern US, western Europe, and eastern China (Yue and Unger, 2014; Lei et al, 2020; Zhu et al, 2021). The damaged vegetation decreases isoprene emissions and stomatal conductance (Wittig et al, 2009; Feng et al, 2019), which influence O3 production and Published by Copernicus Publications on behalf of the European Geosciences Union. Weakened leaf-level transpiration following O3 damage modulates meteorological parameters, such as surface air temperature and atmospheric relative humidity, leading to substantial biogeophysical feedbacks on surface O3 (Lombardozzi et al, 2012; Sadiq et al, 2017)
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