Assessing the roles emission sources and atmospheric processes play in simulating <i>δ</i><sup>15</sup>N of atmospheric NO<sub><i>x</i></sub> and NO<sub>3</sub><sup>−</sup> using CMAQ (version 5.2.1) and SMOKE (version 4.6)
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Published:2022-06-01
Issue:10
Volume:15
Page:4239-4258
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ISSN:1991-9603
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Container-title:Geoscientific Model Development
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language:en
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Short-container-title:Geosci. Model Dev.
Author:
Fang HuanORCID, Michalski GregORCID
Abstract
Abstract. Nitrogen oxides (NOx= nitric oxide (NO) + nitrogen dioxide
(NO2)) are important trace gases that affect atmospheric chemistry, air
quality, and climate. Contemporary development of NOx emissions
inventories is limited by the understanding of the roles of vegetation (net
NOx source or net sink), vehicle emissions from gasoline- and
diesel-powered vehicles, the application of NOx emission control
technologies, and accurate verification techniques. The nitrogen stable
isotope composition (δ15N) of NOx is an effective tool to
evaluate the accuracy of the NOx emission inventories, which are based
on different assumptions. In this study, we traced the changes in δ15N values of NOx along the “journey” of atmospheric NOx,
driven by atmospheric processes after different sources emit NOx into the
atmosphere. The 15N was incorporated into the emission input dataset,
generated from the US EPA trace gas emission model SMOKE (Sparse Matrix
Operator Kernel Emissions). Then the 15N-incorporated emission input
dataset was used to run the CMAQ (Community Multiscale Air Quality) modeling
system. By enhancing NOx deposition, we simulated the expected δ15N of NO3-, assuming no isotope fractionation during
chemical conversion or deposition. The simulated spatiotemporal patterns in
NOx isotopic composition for both SMOKE outputs (simulations under
the “emission only” scenario) and CMAQ outputs (simulations under the “emission
+ transport + enhanced NOx loss” scenario) were compared with
corresponding measurements in West Lafayette, Indiana, USA. The simulations
under the emission + transport + enhanced NOx loss scenario were
also compared to δ15N of NO3- at NADP (National
Atmospheric Deposition Program) sites. The results indicate the potential
underestimation of emissions from soil, livestock waste, off-road vehicles,
and natural-gas power plants and the potential overestimation of emissions
from on-road vehicles and coal-fired power plants, if only considering the
difference in NOx isotopic composition for different emission sources.
After considering the mixing, dispersion, transport, and deposition of
NOx emission from different sources, the estimation of atmospheric
δ15N(NOx) shows better agreement (by ∼ 3 ‰) with observations.
Funder
Purdue Research Foundation Purdue Climate Change Research Center, Purdue University
Publisher
Copernicus GmbH
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