Influence of aerosol chemical composition on N<sub>2</sub>O<sub>5</sub> uptake: airborne regional measurements in northwestern Europe
Aerosol chemical composition was found to influence nighttime atmospheric chemistry during a series of airborne measurements in northwestern Europe in summer conditions, which has implications for regional air quality and climate. The uptake of dinitrogen pentoxide, γ (N<sub>2&...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/15/973/2015/acp-15-973-2015.pdf |
| Summary: | Aerosol chemical composition was found to influence nighttime atmospheric chemistry during
a series of airborne measurements in northwestern Europe in summer conditions, which has
implications for regional air quality and climate. The uptake of dinitrogen pentoxide, γ
(N<sub>2</sub>O<sub>5</sub>), to particle surfaces was found to be modulated by the amount of water
content and ammonium nitrate present in the aerosol. The conditions prevalent in this study
suggest that the net uptake rate of N<sub>2</sub>O<sub>5</sub> to atmospheric aerosols was relatively
efficient compared to previous studies, with γ (N<sub>2</sub>O<sub>5</sub>) values in the range
0.01–0.03. This is likely a consequence of the elevated relative humidity in the region, which
promotes greater aerosol water content. Increased nitrate concentrations relative to particulate
water were found to suppress N<sub>2</sub>O<sub>5</sub> uptake. The results presented here contrast with
previous ambient studies of N<sub>2</sub>O<sub>5</sub> uptake, which have generally taken place in
low-nitrate environments in the USA. Comparison of the N<sub>2</sub>O<sub>5</sub> uptake derived from the
measurements with a parameterised scheme that is based on the ratio of particulate water to
nitrate yielded reasonably good agreement in terms of the magnitude and variation in uptake,
provided the effect of chloride was neglected. An additional suppression of the parameterised
uptake is likely required to fully capture the variation in N<sub>2</sub>O<sub>5</sub> uptake, which could
be achieved via the known suppression by organic aerosol. However, existing parameterisations
representing the suppression by organic aerosol were unable to fully represent the variation in
N<sub>2</sub>O<sub>5</sub> uptake. These results provide important ambient measurement constraint on our
ability to predict N<sub>2</sub>O<sub>5</sub> uptake in regional and global aerosol
models. N<sub>2</sub>O<sub>5</sub> uptake is a potentially important source of nitrate aerosol and a sink
of the nitrate radical, which is the main nocturnal oxidant in the atmosphere. The results further
highlight the importance of ammonium nitrate in northwestern Europe as a key component of
atmospheric composition in the region. |
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| ISSN: | 1680-7316 1680-7324 |