A038-0002
Soil NO emissions in a SE Australian Eucalypt Forest

Tuesday, 8 December 2020
Poster
Hyunjin An1, Kirsti Ashworth2, Thomas King1, Frances Phillips3, Clare Paton-Walsh4 and Kathryn Emmerson5, (1)University of Lancaster, Lancaster, United Kingdom, (2)Lancaster University, Lancaster Environment Centre, Lancaster, United Kingdom, (3)University of Wollongong, Wollongong, Australia, (4)University of Wollongong, Centre for Atmospheric Chemistry, School of Chemistry, Wollongong, NSW, Australia, (5)CSIRO Marine and Atmospheric Research, Aspendale, Australia
Abstract:
Nitrogen oxides (NOx=NO+NO2) play a pivotal role in the tropospheric oxidation reactions of volatile organic compounds (VOCs), resulting in the formation of ozone and secondary organic aerosol. Although >90% of NOx is released through anthropogenic activities, natural sources, e.g. soils, lightning, contribute most of the reactive nitrogen in rural and remote areas. The emissions of NOx from forest soils are often ignored and,hence, are not well-understood. However, as the world’s forests contribute roughly 80% of global terpenoid emissions, a highly reactive group of VOCs that are estimated to increase the atmospheric lifetime of methane by 10-12 years, it is critical to fully characterize all in-situ sources and sinks of reactive nitrogen.

We deployed a pair of soil chambers (Lancaster University Dynamic Soil Chambers (LU-DySC)) and NOx analysers to measure NO and NO2 concentrations above the soil during the Characterising Organics and Aerosol Loading over Australia (COALA) 2020 field campaign at Cataract Scout Camp, New South Wales, between January and March 2020. The first of the chambers was installed on 2 sets of collars (with and without leaf litter) ~100m from the main measurement site on a daily rotating basis. The second chamber which had an integral base separating it from the soil, was simultaneously deployed to provide an ambient NOx measurement for reference.

Sample concentrations of NO and NO2 were 0.24 and 1.63 ppbv, much lower than recorded at the main observation site. However, there was a clear diel pattern in both NO and NO2 concentrations in the soil chambers, which were less variable than ambient levels and well correlated with photosynthetically active radiation (PAR). The profiles, with a pronounced midday peak, are typical of biogenic emissions. The difference between the sample and the reference chamber indicates flux of NOx. From comparison with ambient concentrations, we deduce a positive (emission) flux of NO from the soil, and negative (loss) of NO2 at soil-level. NO fluxes were higher from “no litter” than “with litter” soil collars, suggesting a possible chemical loss due to VOC emissions from the litter.

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