Modeling Gaseous Nitrogen Emissions from Soils and Their Impacts on Atmospheric Chemistry

BRIAN GAUDET, ManishKumar Shrivastava, Jie Zhang, Quazi Rasool, Jerome Fast, Rahul Zaveri, Sheng-Lun Tai, Pacific Northwest National Laboratory

     Abstract Number: 399
     Working Group: Bioaerosols in Agriculture: Sources, Risks and Mitigation

Abstract
Near urban areas, anthropogenic emissions of oxides of nitrogen (NO) are often the dominant contributor to atmospheric NOx chemistry, however, in rural areas away from urban centers, emissions of NO from soil due to microbial processes could be significant. Soil microbial nitrogen emissions have been thought to make up 20-25% of total NO emissions globally. These emissions are a product of both nitrification and denitrification processes in the soil, but the relative rates of emissions of different nitrogen-containing species (e.g., NO, NH3, HONO, N2) are functions of soil properties such as temperature, moisture content, pH, and soil carbon and nitrogen pools. Within chemical transport models, when soil NO emissions are included, these emissions are frequently expressed as simple functions of available soil nitrogen. However, realistic simulations of the contributions of soil NO emissions to atmospheric chemistry at regional and subannual temporal scales requires representing the impacts of the variations in soil temperature and moisture content on soil nitrification and denitrification rates. Towards that end, we have implemented mechanistic soil NO and NH3 parameterizations that are calculated online using inputs from geographical databases and from an explicit soil biogeochemical model within the Weather Research and Forecasting Model coupled to Chemistry (WRF-Chem). We then simulate both the spring and summer times during the 2016 HISCALE field campaign over the Southern Great Plains (SGP), and evaluate the predicted concentrations of various species (NOx, ozone, aerosols) against measurements. We show how the differences in the meteorology during the spring and summer lead to differences in the contributions of soil NO emissions to atmospheric chemistry, and highlight large regional differences due to heterogeneous soil surface properties.