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| Titel |
Physical and chemical properties of the regional mixed layer of Mexico's Megapolis Part II: evaluation of measured and modeled trace gases and particle size distributions |
| VerfasserIn |
C. Ochoa, D. Baumgardner, M. Grutter, J. Allan, J. Fast, B. Rappenglueck |
| 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 ; 12, no. 21 ; Nr. 12, no. 21 (2012-11-05), S.10161-10179 |
| Datensatznummer |
250011559
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| Publikation (Nr.) |
 copernicus.org/acp-12-10161-2012.pdf |
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| Zusammenfassung |
This study extends the work of Baumgardner et al. (2009) in which
measurements of trace gases and particles, at a remote, high altitude
mountain site, 60 km from Mexico City were analyzed with respect to the
origin of the air masses. In the current evaluation, the temperature, water
vapor mixing ratio (WMR), ozone (O3), carbon monoxide (CO), sulfur
dioxide (SO2) and acyl peroxy nitrate (APN) are simulated with the
WRF-Chem chemical transport model and compared with the measurements at the
mountain site. Comparisons between the model and measurements are also
evaluated for particle size distributions (PSDs) of the mass concentrations
of sulfate, nitrate, ammonium and organic mass (OM). The model predictions
of the diurnal trends in temperature, WMR and trace gases were generally
well correlated; 13 of the 18 correlations were significant at a confidence
level of <0.01. Less satisfactory were the average hourly differences
between model and measurements that showed predicted values within expected,
natural variation for only 10 of the 18 comparisons. The model performed
best when comparing with the measurements during periods when the air
originated from the east. In that case all six of the parameters being
compared had average differences between the model and measurements less
than the expected standard deviation. For the cases when the air masses are
from the southwest or west northwest, only two of the comparisons from each
case showed differences less than the expected standard deviation. The
differences appear to be a result of an overly rapid growth of the boundary
layer predicted by the model and too much dilution. There also is more
O3 being produced, most likely by photochemical production, downwind of
the emission sources than is predicted by the model.
The measured and modeled PSD compare very well with respect to their general
shape and the diameter of the peak concentrations. The spectra are log
normally distributed with most of the mass in the accumulation mode centered
at 200 ± 20 nm and little observed or predicted changes with respect to
the time when the RML is above the Altzomoni research station. Only the
total mass changes with time and air mass origin. The invariability of
average diameter of the accumulation mode suggests that there is very little
growth of the particles by condensation or coagulation after six hours of
aging downwind of the major sources of anthropogenic emissions in Mexico's
Megapolis. This could greatly simplify parameterization in climate models
although it is not known at this time if this invariance can be extended to
other megacity regions. |
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