Development of a chlorine chemistry module for the Master Chemical Mechanism
The chlorine atom (Cl·) has a high potential to perturb atmospheric photochemistry by oxidizing volatile organic compounds (VOCs), but the exact role it plays in the polluted troposphere remains unclear. The Master Chemical Mechanism (MCM) is a near-explicit mechanism that has been widely...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-10-01
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| Series: | Geoscientific Model Development |
| Online Access: | http://www.geosci-model-dev.net/8/3151/2015/gmd-8-3151-2015.pdf |
| Summary: | The chlorine atom (Cl·) has a high potential to perturb
atmospheric photochemistry by oxidizing volatile organic compounds (VOCs),
but the exact role it plays in the polluted troposphere remains unclear. The
Master Chemical Mechanism (MCM) is a near-explicit mechanism that has been
widely applied in the atmospheric chemistry research. While it addresses
comprehensively the chemistry initiated by the OH, O<sub>3</sub> and NO<sub>3</sub>
radicals, its representation of the Cl· chemistry is incomplete as
it only considers the reactions for alkanes. In this paper, we develop a
more comprehensive Cl· chemistry module that can be directly
incorporated within the MCM framework. A suite of 205 chemical reactions
describes the Cl·-initiated degradation of alkenes, aromatics,
alkynes, aldehydes, ketones, alcohols, and some organic acids and nitrates,
along with the inorganic chemistry involving Cl· and its
precursors. To demonstrate the potential influence of the new chemistry
module, it was incorporated into a MCM box model to evaluate the impacts of
nitryl chloride (ClNO<sub>2</sub>), a product of nocturnal halogen activation by
nitrogen oxides (NO<sub><i>X</i></sub>), on the following day's atmospheric
photochemistry. With constraints of recent observations collected at a
coastal site in Hong Kong, southern China, the modeling analyses suggest
that the Cl· produced from ClNO<sub>2</sub> photolysis may substantially
enhance the atmospheric oxidative capacity, VOC oxidation and O<sub>3</sub>
formation, particularly in the early morning period. The results demonstrate
the critical need for photochemical models to include more detailed chlorine
chemistry in order to better understand the atmospheric photochemistry in
polluted environments subject to intense emissions of NO<sub><i>X</i></sub>, VOCs and
chlorine-containing constituents. |
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| ISSN: | 1991-959X 1991-9603 |