Research brief: Soil emissions increase nitrogen oxide in lower atmosphere

Soils have long been considered a significant source of reactive nitrogen to the atmosphere, but quantifying their emissions and impact has proven challenging. Through their reactivity, nitrogen radicals such as nitrous acid (HONO) can strongly influence the oxidation chemistry of the lower atmosphere, but this same reactivity makes them difficult to measure.

Over a three-month campaign in summer and autumn 2017, we measured nitrogen oxides including HONO at Broadmeadows, in northern Melbourne, using the MAX-DOAS technique. This spectroscopic method, which uses scattered sunlight measured at different viewing angles, to reconstruct the vertical distribution of atmospheric gases.

Our results showed consistently high daytime levels of HONO close to the ground at Broadmeadows, which could not be explained using the known chemical mechanisms but showed a strong dependence on the local soil moisture content.

This finding suggests that soil emissions may be increasing the oxidising capacity and nitrogen oxide content of the lower atmosphere. Ongoing measurements and modelling will seek to uncover what impact this may have on other important atmospheric constituents including ozone, and the the associated levels of pollution in Melbourne.


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