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Natural and Anthropogenic Impacts on Global Tropospheric OH and Methane Lifetime: A Multi-Model Analysis From AerChemMIP
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DOI：10.1029/2025JD045874.png)
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Abstract
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This study assesses the influence of natural and anthropogenic emissions on tropospheric hydroxyl radical concentrations ([OH]) and methane (CH4) lifetime using multi-model simulations from the AerChemMIP experiments of CMIP6. Compared to the preindustrial era, we find that 2014-level anthropogenic emissions, which increase global [OH] by 1.1 (0.7-2.1) & times; 105 molecules cm-3, and doubled natural emissions, which decrease global [OH] by 0.9 (0.2-1.4) & times; 105 molecules cm-3, have comparable impacts on global [OH] and CH4 lifetime. The impact of both anthropogenic and natural emissions reflects a complex counterbalance among different sources. Doubling biogenic non-methane volatile organic compounds (NMVOCs) and lightning NOx (LNOx) results in a 2.5 (1.3-3.0) & times; 105 molecules cm-3 decrease and a 2.1 (1.6-2.6) & times; 105 molecules cm-3 increase in global [OH], respectively, and these are the primary natural factors regulating [OH]. Anthropogenic emissions primarily affect [OH] through near-term climate forcers (NTCFs), increasing [OH] by 2.5 (2.0-3.7) & times; 105 molecules cm-3, partially offset by well-mixed greenhouse gases. Among NTCFs, NOx and NMVOC emissions dominate, increasing global [OH] by 4.5 (3.2-6.1) & times; 105 molecules cm-3 and decreasing it by 1.8 (1.5-2.3) & times; 105 molecules cm-3, respectively. Regionally, anthropogenic emissions increase the North to South ratio of [OH], whereas natural emissions decrease it. The global [OH] under preindustrial conditions shows 1%-2% interannual variability, with upper-tropospheric variations primarily driven by lightning NOx. The global [OH] is nearly five times more sensitive per Tg N to LNOx than to anthropogenic NOx, highlighting the importance of accurately representing natural emissions to better constrain [OH].
Keywords:
methane
natural emissions
anthropogenic emissions
hydroxyl radical
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