Soil nitrites influence atmospheric chemistry

Public discussion of climate change typically revolves around greenhouse gases, aerosol particles, and the role of human actions (1–3), but it is just beginning to reflect an awareness of the important role played by the global nitrogen cycle (4). It has been difficult, however, to disentangle the nitrogen cycle's role in climate change owing to its complex interactions with other biogeochemical cycles, including the carbon and sulfur cycles (5), and with factors such as soil, vegetation, and water. These interactions can lead to unexpected, nonlinear responses in the Earth system as a whole. On page 1616 of this issue, Su et al. (6) illuminate one poorly understood set of interactions, showing that nitrite in soil can produce nitrous acid (HONO) emissions that are a source of hydroxyl (OH) radicals in the atmosphere. The finding helps identify one source of “missing” atmospheric HONO, and highlights how HONO emissions could rise with increasing temperatures and nitrogen fertilizer use.