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- Title
iNRACM: incorporating 15N into the Regional Atmospheric Chemistry Mechanism (RACM) for assessing the role photochemistry plays in controlling the isotopic composition of NOx, NOy, and atmospheric nitrate.
- Authors
Fang, Huan; Walters, Wendell W.; Mase, David; Michalski, Greg
- Abstract
Nitrogen oxides, classified as NO x (nitric oxide (NO) + nitrogen dioxide (NO 2)) and NO y (NO x+ NO 3 , N 2 O 5 HNO 3 , + HNO 4+ HONO + Peroxyacetyl nitrate (PAN) + organic nitrates + any oxidized N compound), are important trace gases in the troposphere, which play an important role in the formation of ozone, particulate matter (PM), and secondary organic aerosols (SOA). There remain many uncertainties in the origin and fate of atmospheric N compounds including the understanding of NO y cycling, NO x emission budgets, unresolved issues within the heterogeneous uptake coefficients of N 2 O 5 , and the formation of organic nitrates in urban forests, to name a few. A potential tool to resolve some of these uncertainties are using natural abundance N isotopes in NO y compounds. Here we have developed a photochemical mechanism used to simulate tropospheric photochemistry to include 15 N compounds and reactions as a means to simulate δ15 N values in NO y compounds. The 16 N compounds and 96 reactions involving N used in the Regional Atmospheric Chemistry Mechanism (RACM) were replicated using 15 N in a new mechanism called i N RACM. The 192 N reactions in i N RACM were tested to see if isotope effects were relevant with respect to significantly changing the δ15 N values (±1 ‰) of NO x , HONO, and/or HNO 3. The isotope fractionation factors (α) for relevant reactions were assigned based on recent experimental or calculated values. Each relevant reaction in the i N RACM mechanism was tested individually and in concert in order to assess the controlling reactions. The controlling reactions and their diurnal importance are discussed. A comparison between i N RACM predictions and observed δ15 N NO 3- in particulate matter from Tucson, Arizona, suggests the model, and isotope fractionation factors incorporated into it, are accurately capturing the isotope effects occurring during the photochemistry of NO y. The implication is that measurements of δ15 N in NO y compounds may be a new way of tracing in situ N chemistry and a means of assessing NO x emission budgets.
- Subjects
ATMOSPHERIC chemistry; PARTICULATE matter; TRACE gases; NITRIC oxide; ISOTOPIC fractionation; AIR pollutants; PEROXYACETYL nitrate; PHOTOCHEMISTRY
- Publication
Geoscientific Model Development, 2021, Vol 14, Issue 8, p5001
- ISSN
1991-959X
- Publication type
Article
- DOI
10.5194/gmd-14-5001-2021