Active Nitrogen Cycle Driven by Solar Radiation in Clean Desert Air

Deserts have been recognized as constantly releasing reactive nitrogen compounds to the atmosphere due to the subsoil-storage leaching and surface-deposit evaporation induced by solar radiative heating. However, this release and the consequent response of the nitrogen cycles in desert air have not been evaluated and are overlooked in most regional and global models. In our nitrate measurements, including nitric acid and particulate nitrate, in clean air, that is, in the absence of or with minor anthropogenic influences, in a Chinese desert, diurnal nitrate variations consisting of daytime increases and nighttime decreases were observed in the range of 1.3–3.7 μgm⁻³ in summer, 0.1–2.6 μgm⁻³ in spring, and 0.2–1.3 μgm⁻³ in autumn. These values are considerably higher than those observed in remote marine and forest areas. Simulations with a regional transport model demonstrate that the variation could be largely accounted for by the oxidation of soil-emitted reactive nitrogen compounds by photochemical-reactions products. These results indicate an active nitrogen cycle in clean desert air, which is the consequence of the coordination of solar radiation-induced surface soil emission and subsequent photochemical reactions. Satellite data of NO₂ further indicate possible similar cycles in most major desert areas worldwide. By including this nitrogen cycle in the vast desert areas and its subsequent effects, such as those on ozone chemistry, climate models may thus provide a better understanding of the global nitrogen budget in the historical and developing Earth ecosystems.