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| Titel |
Evaluation of mobile emissions contributions to Mexico City's emissions inventory using on-road and cross-road emission measurements and ambient data |
| VerfasserIn |
M. Zavala, S. C. Herndon, E. C. Wood, T. B. Onasch, W. B. Knighton, L. C. Marr, C. E. Kolb, L. T. Molina |
| 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 ; 9, no. 17 ; Nr. 9, no. 17 (2009-09-02), S.6305-6317 |
| Datensatznummer |
250007601
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| Publikation (Nr.) |
 copernicus.org/acp-9-6305-2009.pdf |
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| Zusammenfassung |
Mobile emissions represent a significant fraction of the total anthropogenic
emissions burden in the Mexico City Metropolitan Area (MCMA) and, therefore,
it is crucial to use top-down techniques informed by on-road exhaust
measurements to evaluate and improve traditional bottom-up official
emissions inventory (EI) for the city. We present the measurements of
on-road fleet-average emission factors obtained using the Aerodyne mobile
laboratory in the MCMA in March 2006 as part of the MILAGRO/MCMA-2006 field
campaign. A comparison of our on-road emission measurements with those
obtained in 2003 using essentially the same measurement techniques and
analysis methods indicates that, in the three year span, NO emission factors
remain within the measured variability ranges whereas emission factors of
aldehydes and aromatics species were reduced for all sampled driving
conditions.
We use a top-down fuel-based approach to evaluate the mobile emissions from
the gasoline fleet estimated in the bottom-up official 2006 MCMA mobile
sources. Within the range of measurement uncertainties, we found probable
slight overpredictions of mean EI estimates on the order of 20–28% for CO
and 14–20% for NO. However, we identify a probable EI discrepancy of VOC
mobile emissions between 1.4 and 1.9; although estimated benzene and toluene
mobile emissions in the inventory seem to be well within the uncertainties
of the corresponding emissions estimates. Aldehydes mobile emissions in the
inventory, however, seem to be underpredicted by factors of 3 for HCHO and 2
for CH3CHO. Our on-road measurement-based estimate of annual emissions
of organic mass from PM1 particles suggests a severe underprediction
(larger than a factor of 4) of PM2.5 mobile emissions in the inventory.
Analyses of ambient CO, NOx and CO/NOx concentration trends in the
MCMA indicate that the early morning ambient CO/NOx ratio has decreased
at a rate of about 1.9 ppm/ppm/year over the last two decades due to
reductions in CO levels rather than by NOx. These trends, together with
the analysis of fuel sales and fleet size, suggest that the relative
contribution of diesel vehicles to overall NOx levels has increased
over time in the city. Despite the impressive increase in the size of the
vehicle fleet between 2000 and 2006, the early morning ambient
concentrations of CO and NOx have not increased accordingly, probably
due to the reported low removal rates of older vehicles, which do not have
emissions control technologies, and partially due to the much lower
emissions from newer gasoline vehicles. This indicates that an
emission-based air quality improvement strategy targeting large reductions
of emissions from mobile sources should be directed towards a significant
increase of the removal rate of older, highly-polluting, vehicles. |
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