Global and Regional Patterns of Soil Nitrous Acid Emissions and Their Acceleration of Rural Photochemical Reactions

Abiotic and biotic releases of nitrous acid (HONO) from soils contribute substantially to the missing source of tropospheric HONO and hydroxyl radicals (OH). However, global and regional patterns of soil HONO emissions are rarely quantified, and the contributions of such emissions to atmospheric oxidization capacity are unclear. Here, we present that the best estimate of global soil HONO emissions in 2017 was 9.67 with a range of 7.36–11.99 Tg N yr⁻¹, and cropland soils accounting for ∼79%. The analyses also indicate that regional soil HONO emissions enhanced ground OH concentrations by 10%–60% and ozone concentrations by 0.5–1.5 ppb in daytime in the ambient area of Shanghai, China. The impact of soil HONO emissions on OH budgets was more significant in rural than urban areas. These findings suggest that the soil HONO emissions, especially from cropland, could quicken photochemical reactions, and aggravate air pollution in rural areas.