Erschienen in:
Biogeosciences, 16 (2019) 9, Seite 2003-2031
Sprache:
Englisch
DOI:
10.5194/bg-16-2003-2019
ISSN:
1726-4189
Entstehung:
Anmerkungen:
Beschreibung:
Abstract. The reactive trace gases nitric oxide (NO) and nitrous acid (HONO) arecrucial for chemical processes in the atmosphere, including the formation ofozone and OH radicals, oxidation of pollutants, and atmosphericself-cleaning. Recently, empirical studies have shown that biological soilcrusts are able to emit large amounts of NO and HONO, and they may thereforeplay an important role in the global budget of these trace gases. However,the upscaling of local estimates to the global scale is subject to largeuncertainties, due to unknown spatial distribution of crust types and theirdynamic metabolic activity. Here, we perform an alternative estimate ofglobal NO and HONO emissions by biological soil crusts, using a process-basedmodelling approach to these organisms, combined with global datasets of climate and land cover. We thereby consider that NO and HONO areemitted in strongly different proportions, depending on the type of crust andtheir dynamic activity, and we provide a first estimate of the globaldistribution of four different crust types. Based on this, we estimate globaltotal values of 1.04 Tg yr−1 NO–N and 0.69 Tg yr−1 HONO–Nreleased by biological soil crusts. This corresponds to around 20 % ofglobal emissions of these trace gases from natural ecosystems. Due to the lownumber of observations on NO and HONO emissions suitable to validate themodel, our estimates are still relatively uncertain. However, they areconsistent with the amount estimated by the empirical approach, whichconfirms that biological soil crusts are likely to have a strong impact onglobal atmospheric chemistry via emissions of NO and HONO.