Photochemical emission and fixation of NOX gases in soils

Abstract

Gaseous nitrogen oxides (NOx), which result from combustion of fossil fuels, volcanic eruptions, forest fires, and biological reactions in soils, not only affect air quality and the atmospheric concentration of ozone, but also contribute to global warming and acid rain. We provide evidence of gas exchange in soils involving emissions of NOx by effect of photochemical reactions, and their counterpart fixation through photocatalytic reactions under UV-Visible irradiation. The catalytic activity promoting NOx capture as nitrate varied widely amongst different soil types, from low in quartzitic sandy soils to high in iron oxide and TiO2 rich soils. Clay soils with significant amounts of smectite also exhibited high rates of NOx sequestration and fixed amounts of N comparable to NO (nitric oxide) losses through biotic reactions. This mechanism of N fixation provides a new insight into the nitrogen cycle and may inspire alternative strategies to reduce NO emissions from soils.