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| Titel |
Seasonal and diurnal trends in black carbon properties and co-pollutants in Mexico City |
| VerfasserIn |
A. Retama, D. Baumgardner, G. B. Raga, G. R. McMeeking, J. W. Walker |
| 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. 16 ; Nr. 15, no. 16 (2015-08-28), S.9693-9709 |
| Datensatznummer |
250120002
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| Publikation (Nr.) |
 copernicus.org/acp-15-9693-2015.pdf |
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| Zusammenfassung |
The Mexico City metropolitan area (MCMA) is a region that continues to grow
in population and vehicular traffic as well as being the largest source of
short-lived climate pollutants (SLCP) in Latin America. The local city
government has made significant progress in controlling some of these
pollutants, i.e., ozone (O3) and carbon monoxide (CO), but particulate
matter (PM2.5 and PM10) and black carbon (BC) have shown a less
positive response to mitigation strategies that have been in place for
almost 3 decades. For the first time, extended measurements of equivalent black
carbon (eBC), derived from light absorption measurements, have been made using a
Photoacoustic Extinctiometer (PAX) over a 13 month
period from March 2013 through March 2014. The daily trends in workdays
(Monday through Saturday) and Sunday eBC, PM2.5 and the co-pollutants
CO, O3 and NOx are evaluated with respect to the three primary
seasons in the MCMA: rainy, cold and dry and warm and dry.
The maximum values in all of the particle and gas concentrations were
significantly larger (Student's t test, P < 0.05) during the dry
periods than in the rainy season. The changes from rainy to dry seasons for
eBC, PM2.5, CO, O3 and NOx were 8.8 to 13.1 μg m−3 (40 %), 49 to 73 μg m−3 (40 %), 2.5 to 3.8 ppm
(40 %), 73 to 100 ppb (30 %) and 144 to 252 ppb (53 %), respectively.
The primary factors that lead to these large changes between the wet and dry
seasons are the accelerated vertical mixing of boundary layer and free
tropospheric air by the formation of clouds that dilutes the concentration
of the SLCPs, the decreased actinic flux that reduces the production of
ozone by photochemical reactions and the heavy, almost daily rain that
removes particulate matter.
A significant "weekend effect" was also identified, particularly the
decrease in BC due to fewer large transport vehicles that are fueled by
diesel, which produces a large fraction of the BC. The other co-pollutant
concentrations are also significantly less on weekends except for O3
that shows no change in maximum values from workdays to Sundays. This lack of
change is a result of the balancing effects of lower precursor gases, i.e.,
VOCs, offset by lower concentrations of NOx, that is an O3
inhibitor.
A comparison of the average maximum value of eBC measured during the 1
year period of the current study, with maximum values measured in shorter
field campaigns in 2000 and 2006, shows no significant change in the eBC
emissions over a 14 year period. This suggests that new methods may need to
be developed that can decrease potentially toxic levels of this particulate
pollutant. |
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