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| Titel |
WRF-Chem model predictions of the regional impacts of N2O5 heterogeneous processes on night-time chemistry over north-western Europe |
| VerfasserIn |
D. Lowe, S. Archer-Nicholls, W. Morgan, J. Allan, S. Utembe, B. Ouyang, E. Aruffo, M. Le Breton, R. A. Zaveri, P. Di Carlo, C. Percival, H. Coe, R. Jones, G. McFiggans |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 3 ; Nr. 15, no. 3 (2015-02-09), S.1385-1409 |
| Datensatznummer |
250119397
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| Publikation (Nr.) |
 copernicus.org/acp-15-1385-2015.pdf |
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| Zusammenfassung |
Chemical modelling studies have been conducted over north-western
Europe in summer conditions, showing that night-time dinitrogen
pentoxide (N2O5) heterogeneous reactive uptake is important
regionally in modulating particulate nitrate and has a~modest
influence on oxidative chemistry. Results from Weather Research and
Forecasting model with Chemistry (WRF-Chem) model
simulations, run with a detailed volatile organic compound (VOC)
gas-phase chemistry scheme and the Model for Simulating Aerosol
Interactions and Chemistry (MOSAIC) sectional aerosol scheme,
were compared with a series of airborne gas and particulate
measurements made over the UK in July 2010. Modelled mixing ratios of
key gas-phase species were reasonably accurate (correlations with
measurements of 0.7–0.9 for NO2 and O3). However
modelled loadings of particulate species were less accurate
(correlation with measurements for particulate sulfate and ammonium
were between 0.0 and 0.6). Sulfate mass loadings were particularly low
(modelled means of 0.5–0.7 μg kg−1air,
compared with measurements of
1.0–1.5 μg kg−1air). Two flights from the
campaign were used as test cases – one with low relative humidity (RH)
(60–70%), the other with high RH (80–90%). N2O5
heterogeneous chemistry was found to not be important in the low-RH
test case; but in the high-RH test case it had a strong effect and
significantly improved the agreement between modelled and measured
NO3 and N2O5. When the model failed to capture
atmospheric RH correctly, the modelled NO3 and N2O5
mixing ratios for these flights differed significantly from the
measurements. This demonstrates that, for regional modelling which
involves heterogeneous processes, it is essential to capture the
ambient temperature and water vapour profiles.
The night-time NO3 oxidation of VOCs across the whole region
was found to be 100–300 times slower than the daytime OH
oxidation of these compounds. The difference in contribution was less
for alkenes (× 80) and comparable for dimethylsulfide (DMS). However the
suppression of NO3 mixing ratios across the domain by
N2O5 heterogeneous chemistry has only a very slight,
negative, influence on this oxidative capacity. The influence on
regional particulate nitrate mass loadings is stronger. Night-time
N2O5 heterogeneous chemistry maintains the production of
particulate nitrate within polluted regions: when this process is
taken into consideration, the daytime peak (for the 95th percentile)
of PM10 nitrate mass loadings remains around
5.6 μg kg−1air, but the night-time minimum
increases from 3.5 to 4.6 μg kg−1air. The
sustaining of higher particulate mass loadings through the night by
this process improves model skill at matching measured aerosol nitrate
diurnal cycles and will negatively impact on regional air quality,
requiring this process to be included in regional models. |
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