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CH4 Boosts the Atmospheric Nitrate-to-HONO Formation by Photoinduced •CH3 Radicals.

Xin Zhang,Hong Wang,Shujun Liu,Yanxia Wang,Meijia Jiang,Jiayan Yu,Miao Feng,Xinwei Li,Fan Dong

Published 2025 in Journal of the American Chemical Society

ABSTRACT

The impact of rising CH4 concentrations has become a key global focus in air pollution and climate change, as its photoconversion generates highly reactive methyl radicals with translational potential. However, the overlooked role of •CH3 radicals on HONO formation has led to the underestimated contribution of greenhouse gases on atmospheric oxidative capacity. Here, we propose a CH4-promoted nitrate photolysis route where the nitrate-to-HONO is significantly promoted, varying from 46.98% to 95.75% as the relative humidity increased. In situ spectroscopic and theoretical analyses reveal that the •CH3 radicals activate the NO3- molecule to facilitate N-O bond cleavage and promote H2O dissociation to supply hydrogen atoms for HONO formation, with pivotal •OH radicals from H2O further enhancing this effect under high RH conditions. We also roughly estimated the enhancement of the atmospheric •OH radical budget by CH4 and confirmed its environmental significance through demonstrations on the surfaces of atmospheric fine particulate matter and industrial photoactive materials. This work underscores the interactive relationship between CH4 and atmospheric oxidative capacity and provides direct evidence for the observed enhancement of atmospheric oxidative capacity contributed by greenhouse gases.

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