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- Title
Assessment of Nocturnal NO<sub>x</sub> Heterogeneous Reaction Mechanisms in the Community Multiscale Air Quality (CMAQ) Model.
- Authors
Hoffman, Alicia; Bertram, Timothy H.; Holloway, Tracey; Harkey, Monica
- Abstract
Nitrogen oxides (NOx) have adverse human health impacts and play a central role in the production of ozone and PM2.5. Nighttime heterogeneous chemistry regulates the nocturnal reservoirs and sinks of NOx such as N2O5 removal and ClNO2 production. However, existing parameterizations of nocturnal NOx heterogeneous chemistry in air quality models do not capture the variability in observations. Here, we implemented for the first time in the Community Multiscale Air Quality (CMAQ) model the Gaston N2O5 uptake (γ(N2O5)) mechanism that accounts for the role of particulate organic matter in regulating N2O5 uptake and the Staudt ClNO2 yield (Φ(ClNO2)) mechanism that includes the role of reactive solutes in suppressing ClNO2 production. With the Gaston and Staudt parameterizations, the coarse mode contributed modestly to N2O5 loss (17.2%) but significantly to ClNO2 production (60.3%), highlighting the impact of coarse mode chemistry. The Gaston γ(N2O5) parameterization in the fine mode increased agreement between modeled N2O5 concentration and observations (RMSEnew = 0.37ppb) compared to the model default (RMSEdefault = 0.43ppb). The Gaston γ(N2O5) parameterization was overall biased low due to underestimates in modeled particle oxygen to carbon ratio (O:C). The Staudt Φ(ClNO2) parameterization resulted in further underestimation (NMBnew = −73.7%) compared to the model default (NMBdefault = −37.9%) because of underestimation of fine mode particle chloride concentration. We expect that the updated parameterizations may more accurately capture the mean state and variability in γ(N2O5) and Φ(ClNO2) under conditions where model particulate O:C and chloride are better represented. Plain Language Summary: Air pollutants such as nitrogen oxides (NOx) are regulated by the U.S. EPA because of their negative human health and environmental impacts. Modeling of NOx chemistry is important for both understanding what leads to air pollution events and assessing how to improve poor air quality. Accurate treatment of relevant nighttime reactions that impact NOx is necessary to reproduce air quality conditions, yet current model representations miss the effects of complex particle composition. We implement two updated mechanisms in the Community Multiscale Air Quality (CMAQ) model that are representative of complex particle chemistry with the goal of improving model predictions of nighttime NOx. The updated mechanisms improved performance of these nighttime reactions compared to existing model mechanisms for some chemical species, but none of the model simulations captured the full range of observed values. Further updates to the model representation of particle composition may result in additional improvements to nighttime NOx chemistry. Key Points: Updated parameterizations for N2O5 uptake and ClNO2 yield in the Community Multiscale Air Quality (CMAQ) model highlight the impact of coarse mode chemistry on NOxThe Gaston N2O5 uptake parameterization in the fine mode increased agreement between modeled and observed N2O5 concentrationModel results show an underestimation of modeled particle oxygen to carbon ratio and fine mode particle chloride concentration
- Subjects
UNITED States. Environmental Protection Agency; AIR quality; NITROGEN oxides; PARTICULATE matter; AIR pollutants; AIR pollution; COMPLEX compounds; CATALYTIC reduction
- Publication
Journal of Geophysical Research. Atmospheres, 2024, Vol 129, Issue 10, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2023JD040290