Background-like nitrate in desert air

摘要

The atmospheric nitrogen cycle is a key process driving the earth's environmental evolution. Current model studies require knowledge of NO_x soil emissions from various land types, but desert emissions remain unquatified or are not addressed with high confidence. Our measurements at two observatories in Taklimakan desert during a dust episode showed an approximately stable and dust-independent nitrate in the air. Its concentration estimated from PM_(2.5), PM_(10) and TCP samples under non-dust, floating dust and dust storm conditions was 3.81 ± 1.24 μg m~(-3), 2.95 ± 0.69 μg m~(-3), 4.99 ± 1.71 μg m~(-3), respectively, despite the more-than-one-order difference of dust loading. This concentration was much larger than that in remote marine and tropical forest air. Comprehensive investigation revealed a similar presence of nitrate in other desert air. The nitrate was hypothesized to be the consequence of the conversion of NO_x released from desert soils. These results indicate a background-like nitrate and active reactions of nitrogen compounds in desert air.