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Modeling and Recent Shift in the Composition of Atmospheric Reactive Nitrogen
Citation:
Bash, J., D. Schwede, E. Cooter, K. Foley, AND Johnt Walker. Modeling and Recent Shift in the Composition of Atmospheric Reactive Nitrogen. Webinar for CENRS Air Quality Research Subcommittee, RTP, NC, April 20, 2017.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Computational Exposure Division (CED) develops and evaluates data, decision-support tools, and models to be applied to media-specific or receptor-specific problem areas. CED uses modeling-based approaches to characterize exposures, evaluate fate and transport, and support environmental diagnostics/forensics with input from multiple data sources. It also develops media- and receptor-specific models, process models, and decision support tools for use both within and outside of EPA.
Description:
Nitrogen is an essential building block of all proteins and thus an essential nutrient for all life. Reactive nitrogen, which is naturally produced via enzymatic reactions, forest fires and lightning, is continually recycled and cascades through air, water, and soil media. Human activity has perturbed this cycle through the combustion of fossil fuels and synthesis of fertilizers. In excess reactive nitrogen can lead to ozone and particulate matter formation in the atmosphere, biodiversity loss in terrestrial ecosystems and eutrophication in aquatic ecosystems. The anthropogenic contribution to this cycle is now larger than natural sources in the United States and globally. There is a need to improve the modeling of the cycling of reactive nitrogen in the environment to better understand how anthropogenic inputs are perturbing air quality and ecosystem health. Here we will present the parameterizations of the multimedia transport processes in the Community Multiscale Air Quality Model and the parameterization of agricultural practices, primarily through mineral fertilizer application to crops, the largest source of environmental reactive nitrogen. Here we will focus on modeling of the atmospheric and soil components of the nitrogen cascade, with an emphasis on ammonia, emerging measurement techniques, and the potential for model improvements using emerging measurements, existing networks and modeling. The U.S. EPA’s Community Mulitscale Air Quality (CMAQ) model will be briefly evaluated against observational trends in total nitrogen deposition and ambient air quality from 2002 to 2012. Recent measurements and our modeling results indicate that atmospheric nitrogen composition and deposition is shifting from oxidized species, largely originating from combustion sources, to reduced nitrogen, largely originating from agricultural practices. The change in the composition of reactive nitrogen and its impact on atmospheric composition and deposition will be explored. We will conclude with an assessment of the progress made to date on the modeling of reactive nitrogen in the environment, recent model development efforts and the research needs to further this research.
