Examining the impact of heterogeneous nitryl chloride production on air quality across the United States
The heterogeneous hydrolysis of dinitrogen pentoxide (N<sub>2</sub>O<sub>5</sub>) has typically been modeled as only producing nitric acid. However, recent field studies have confirmed that the presence of particulate chloride alters the reaction product to produce nitryl chl...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2012-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/12/6455/2012/acp-12-6455-2012.pdf |
| Summary: | The heterogeneous hydrolysis of dinitrogen pentoxide (N<sub>2</sub>O<sub>5</sub>) has
typically been modeled as only producing nitric acid. However, recent field
studies have confirmed that the presence of particulate chloride alters the
reaction product to produce nitryl chloride (ClNO<sub>2</sub>) which undergoes
photolysis to generate chlorine atoms and nitrogen dioxide (NO<sub>2</sub>). Both
chlorine and NO<sub>2</sub> affect atmospheric chemistry and air quality. We
present an updated gas-phase chlorine mechanism that can be combined with
the Carbon Bond 05 mechanism and incorporate the combined mechanism into the
Community Multiscale Air Quality (CMAQ) modeling system. We then update the
current model treatment of heterogeneous hydrolysis of N<sub>2</sub>O<sub>5</sub> to
include ClNO<sub>2</sub> as a product. The model, in combination with a
comprehensive inventory of chlorine compounds, reactive nitrogen,
particulate matter, and organic compounds, is used to evaluate the impact of
the heterogeneous ClNO<sub>2</sub> production on air quality across the United
States for the months of February and September in 2006. The heterogeneous
production increases ClNO<sub>2</sub> in coastal as well as many in-land areas in
the United States. Particulate chloride derived from sea-salts,
anthropogenic sources, and forest fires activates the heterogeneous
production of ClNO<sub>2</sub>. With current estimates of tropospheric emissions,
it modestly enhances monthly mean 8-h ozone (up to 1–2 ppbv or 3–4%) but
causes large increases (up to 13 ppbv) in isolated episodes. This chemistry
also substantially reduces the mean total nitrate by up to 0.8–2.0 μg m<sup>−3</sup>
or 11–21%. Modeled ClNO<sub>2</sub> accounts for up to 6% of the
monthly mean total reactive nitrogen. Sensitivity results of the model
suggest that heterogeneous production of ClNO<sub>2</sub> can further increase
O<sub>3</sub> and reduce TNO<sub>3</sub> if elevated particulate-chloride levels are
present in the atmosphere. |
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| ISSN: | 1680-7316 1680-7324 |