Declining Δ17O of nitrate in the northeastern Tibetan Plateau reveals changing atmospheric oxidative capacity

In recent decades, the warm-wet climate has markedly altered the hydrological and ecological systems of the Tibetan Plateau, potentially leading to changes in its atmospheric oxidative capacity. Stable isotopic compositions (δ15N, δ18O, Δ17O) of atmospheric nitrate can provide direct evidence on nitrogen oxide sources and oxidation pathways. Here we characterize the atmospheric oxidative capacity transformation over the past two decades (2002-2023) in the northeastern Tibetan Plateau by combining nitrate isotopic measurements in an ice core collected in Anemaqen with numerical model (GEOS-Chem) simulations. We observed a decreasing trend in Δ17O-NO3- from 2008 to 2023 and interpreted it as evidence for an increasing importance of the hydroxyl radical in nitrate production. This trend may reflect an enhanced atmospheric oxidative capacity driven by rising humidity and increased microbial nitrogen oxides emissions associated with warming and wetting trends on the Tibetan Plateau. These findings point to a possible sensitivity of regional atmospheric oxidative capacity to climate change. Climatic shift affects the atmospheric oxidative capacity of the Tibetan Plateau, highlighted by an increase in biogenic nitrogen oxides emissions from microbial soil activity, as revealed through nitrate isotopic measurements from an ice core to analyze atmospheric oxidative capacity since 2002.