Impacts of land-use change on century-scale global soil NO x emissions using the biogeochemical model VISIT

Abstract Soils represent a significant natural source of nitric oxide (NO), a precursor of nitrogen oxides (NO x ) that play an essential role in atmospheric chemistry and radiative forcing. However, historical estimates of global soil NO x emissions have been constrained by limited long-term nitrogen input datasets and methodological gaps in process representation. In this study, we present the first century-scale simulation of global soil NO x emissions (1850–2020) using the biogeochemical model VISIT (The Vegetation Integrative SImulator for Trace gases), coupled with the newly developed History of anthropogenic Nitrogen inputs dataset of harmonized anthropogenic nitrogen inputs. Our results reveal that total global soil NO x emissions increased gradually from an average of 22.1 Tg N yr −1 prior to 1900 to 25.3 Tg N yr −1 in the 2010s, with emissions above the canopy ranging from 12.2 to 13.6 Tg N yr −1 . Notably, while soil NO x emissions from natural ecosystems showed a marginal decline, the contribution of agricultural soils experienced a more than fourfold increase to global NO x emissions, driven primarily by fertilizer and manure application since the mid-20th century. This led to a more than fourfold increase in the share of agricultural land in global soil NO x emissions, rising from 7.8% to 31.3%. Regional analysis indicates substantial increases in Europe, Asia, and North America, with soil NO x emissions becoming a dominant source in sparsely populated and arid regions. These findings underscore the growing importance of soil-derived NO x in the global nitrogen budget and its implications for future air quality and climate mitigation strategies. This work provides a robust basis for refining emission inventories and supports the development of region-specific nitrogen management to mitigate unintended NO x emissions from soils. On the other hand, benchmarking against the results in Nitrogen Model Inter-comparison Project (NMIP2) revealed significant divergence in global soil NO x emissions between models, with the VISIT estimates on the higher end, highlighting the urgent need for improved process representation and observational constraints.