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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/gmd-2018-276
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gmd-2018-276
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Development and technical paper 13 Nov 2018

Development and technical paper | 13 Nov 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).

Mechanistic representation of soil nitrogen emissions in the Community Multi-scale Air Quality (CMAQ) model v 5.1

Quazi Z. Rasool1,a, Jesse O. Bash2, and Daniel S. Cohan1 Quazi Z. Rasool et al.
  • 1Department of Civil and Environmental Engineering, Rice University, Houston, Texas, USA
  • 2Computational Exposure Division, National Exposure Research Laboratory, Office of Research and Development, US Environmental Protection Agency, RTP, NC, USA
  • acurrently at: Department of Environmental Science and Engineering, UNC-Chapel Hill, NC, USA

Abstract. Soils are important sources of emissions of nitrogen (N)-containing gases such as nitric oxide (NO), nitrous acid (HONO), nitrous oxide (N2O), and ammonia (NH3). However, most contemporary air quality models lack a mechanistic representation of the biogeochemical processes that form these gases. They typically use heavily parameterized equations to simulate emissions of NO independently from NH3, and do not quantify emissions of HONO or N2O. This study introduces a mechanistic, process-oriented representation of soil emissions of N species (NO, HONO, N2O, and NH3) that we have recently implemented in the Community Multi-scale Air Quality (CMAQ) model. The mechanistic scheme accounts for biogeochemical processes for soil N transformations such as mineralization, volatilization, nitrification, and denitrification. The rates of these processes are influenced by soil parameters, meteorology, land use, and mineral N availability. We account for spatial heterogeneity in soil conditions and biome types by using a global dataset for soil carbon (C) and N across terrestrial ecosystems to estimate daily mineral N availability in non-agricultural soils, which was not accounted in earlier parameterizations for soil NO. Our mechanistic scheme also uses daily year-specific fertilizer use estimates from the Environmental Policy Integrated Climate (EPIC v.0509) agricultural model. A soil map with sub-grid biome definitions was used to represent conditions over the continental United States. CMAQ modeling for May and July 2011 shows improvement in model performance in simulated NO2 columns compared to Ozone Monitoring Instrument (OMI) satellite retrievals for regions where soils are the dominant source of NO emissions. We also assess how the new scheme affects model performance for NOx (NO+NO2), fine nitrate (NO3) particulate matter, and ozone observed by various ground-based monitoring networks. Soil NO emissions in the new mechanistic scheme tend to fall between the magnitudes of the previous parametric schemes and display much more spatial heterogeneity. The new mechanistic scheme also accounts for soil HONO, which had been ignored by parametric schemes.

Quazi Z. Rasool et al.
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Quazi Z. Rasool et al.
Data sets

Mechanistic representation of soil nitrogen emissions in CMAQ version 5.1 Q. Z. Rasool, J. O. Bash, and D. S. Cohan https://doi.org/10.3334/ORNLDAAC/1661

Model code and software

Mechanistic representation of soil nitrogen emissions in CMAQ version 5.1 Q. Z. Rasool, J. O. Bash, and D. S. Cohan https://doi.org/10.3334/ORNLDAAC/1661

Quazi Z. Rasool et al.
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Short summary
Soils are long overlooked as source of reactive nitrogen (N) emissions that get pronounced in summer ozone season (growing season) and increasingly important as fertilizer use grows, while fossil fuel combustion sources of N decline. Mechanistic process models of soil N emissions are used in earth science and soil biogeochemical modeling, on a site scale. This work mechanistically models soil N emissions for the first time on a regional scale to better understand their air quality impacts.
Soils are long overlooked as source of reactive nitrogen (N) emissions that get pronounced in...
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