Sensitivity of a global model to the uptake of N<sub>2</sub>O<sub>5</sub> by tropospheric aerosol
The uptake of N<sub>2</sub>O<sub>5</sub> on aerosol impacts atmospheric concentrations of NO<sub>x</sub> and so O<sub>3</sub>, OH, and hence CH<sub>4</sub>. Laboratory studies show significant variation in the rate of uptake, with a general...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2010-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/10/7409/2010/acp-10-7409-2010.pdf |
| Summary: | The uptake of N<sub>2</sub>O<sub>5</sub> on aerosol impacts atmospheric concentrations of NO<sub>x</sub> and so O<sub>3</sub>, OH, and hence CH<sub>4</sub>. Laboratory studies show significant variation in the rate of uptake, with a general decline in the value of γ<sub>N<sub>2</sub>O<sub>5</sub></sub> over the last decade as increasingly relevant tropospheric proxies have been studied. In order to understand the implication of this decline for tropospheric composition, a global model of tropospheric chemistry and transport (GEOS-Chem) is run with differing values of γ<sub>N<sub>2</sub>O<sub>5</sub></sub> (0.0, 10×10<sup>−6</sup>, 10×10<sup>−4</sup>, 10<sup>−3</sup>, 5×10<sup>−3</sup>, 10<sup>−2</sup>, 2×10×10<sup>−2</sup>, 0.1, 0.2, 0.5, and 1.0). We identify three regimes in the model response. At low values of γ<sub>N<sub>2</sub>O<sub>5</sub></sub>, the model shows reduced sensitivity to the value of γ<sub>N<sub>2</sub>O<sub>5</sub></sub> as heterogeneous uptake of γ<sub>N<sub>2</sub>O<sub>5</sub></sub> does not provide a significant pathway to perturb NO<sub>x</sub> burdens. At high values of γ<sub>N<sub>2</sub>O<sub>5</sub></sub> the model again shows reduced sensitivity to the value of γ<sub>N<sub>2</sub>O<sub>5</sub></sub>, as NO<sub>x</sub> loss through heterogeneous removal of γ<sub>N<sub>2</sub>O<sub>5</sub></sub> is limited by the rate of production of NO<sub>3</sub>, rather than the rate of heterogeneous uptake. At intermediate values of γ<sub>N<sub>2</sub>O<sub>5</sub></sub> the model shows significant sensitivity to the value of γ<sub>N<sub>2</sub>O<sub>5</sub></sub>. We find regional differences in the model's response to changing γ<sub>N<sub>2</sub>O<sub>5</sub></sub>. Regions with high aerosol surface area and low temperatures show NO<sub>3</sub> production becoming rate limiting at lower γ<sub>N<sub>2</sub>O<sub>5</sub></sub> values than regions with lower aerosol surface area and higher temperatures. The northern extra-tropics show significant sensitivity to the value of γ<sub>N<sub>2</sub>O<sub>5</sub></sub> at values consistent with current literature (0.001–0.02), thus an accurate description of γ<sub>N<sub>2</sub>O<sub>5</sub></sub> is required for adequate simulation of O<sub>3</sub> burdens and long-range transport of pollutants in this region. <br><br> Our model simulations also provide insight into the sensitivity of coupled chemistry-aerosol simulations to the choice of γ<sub>N<sub>2</sub>O<sub>5</sub></sub>. We find little change in the global sensitivity of NO<sub>x</sub>, O<sub>3</sub> and OH to γ<sub>N<sub>2</sub>O<sub>5</sub></sub> in the range 0.05 to 1.0, but a significant drop in sensitivity below this range. Thus simulations of the coupled impact of both chemistry and aerosol changes through time will be sensitive to the choice of γ<sub>N<sub>2</sub>O<sub>5</sub></sub>. |
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| ISSN: | 1680-7316 1680-7324 |