Global impacts of tropospheric halogens (Cl, Br, I) on oxidants and composition in GEOS-Chem
Item
Title (Dublin Core)
Global impacts of tropospheric halogens (Cl, Br, I) on oxidants and composition in GEOS-Chem
Description (Dublin Core)
We present a simulation of the global present-day composition of the troposphere which includes the chemistry of halogens (Cl, Br, I). Building on previous work within the GEOS-Chem model we include emissions of inorganic iodine from the oceans, anthropogenic and biogenic sources of halogenated gases, gas phase chemistry, and a parameterised approach to heterogeneous halogen chemistry. Consistent with Schmidt et al. (2016) we do not include sea-salt debromination. Observations of halogen radicals (BrO, IO) are sparse but the model has some skill in reproducing these. Modelled IO shows both high and low biases when compared to different datasets, but BrO concentrations appear to be modelled low. Comparisons to the very sparse observations dataset of reactive Cl species suggest the model represents a lower limit of the impacts of these species, likely due to underestimates in emissions and therefore burdens. Inclusion of Cl, Br, and I results in a general improvement in simulation of ozone (O<sub>3</sub>) concentrations, except in polar regions where the model now underestimates O<sub>3</sub> concentrations. Halogen chemistry reduces the global tropospheric O<sub>3</sub> burden by 18.6 %, with the O<sub>3</sub> lifetime reducing from 26 to 22 days. Global mean OH concentrations of 1.28 × 10<sup>6</sup> molecules cm<sup>−3</sup> are 8.2 % lower than in a simulation without halogens, leading to an increase in the CH<sub>4</sub> lifetime (10.8 %) due to OH oxidation from 7.47 to 8.28 years. Oxidation of CH<sub>4</sub> by Cl is small (∼ 2 %) but Cl oxidation of other VOCs (ethane, acetone, and propane) can be significant (∼ 15–27 %). Oxidation of VOCs by Br is smaller, representing 3.9 % of the loss of acetaldehyde and 0.9 % of the loss of formaldehyde.
Creator (Dublin Core)
Sherwen, Tomás
Schmidt, Johan A.
Evans, Mat J.
Carpenter, Lucy J.
Großmann, Katja
Eastham, Sebastian D.
Jacob, Daniel J.
Dix, Barbara
Koenig, Theodore K.
Sinreich, Roman
Ortega, Ivan
Volkamer, Rainer
Saiz-Lopez, Alfonso
Prados-Roman, Cristina
Mahajan, Anoop S.
Ordóñez, Carlos
Date (Dublin Core)
2018-11-01
Type (Dublin Core)
Text
Format (Dublin Core)
application/pdf
Identifier (Dublin Core)
10.5194/acp-16-12239-2016
https://acp.copernicus.org/articles/16/12239/2016/
Source (Dublin Core)
eISSN: 1680-7324
Language (Dublin Core)
eng
