Evaluation of mobile emissions contributions to Mexico City's emissions inventory using on-road and cross-road emission measurements and ambient data

dc.contributor.authorZavala, M.en
dc.contributor.authorHerndon, S. C.en
dc.contributor.authorWood, E. C.en
dc.contributor.authorOnasch, T. B.en
dc.contributor.authorKnighton, W. B.en
dc.contributor.authorMarr, Linsey C.en
dc.contributor.authorKolb, C. E.en
dc.contributor.authorMolina, L. T.en
dc.contributor.departmentCivil and Environmental Engineeringen
dc.description.abstractMobile 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 CH(3)CHO. Our on-road measurement-based estimate of annual emissions of organic mass from PM(1) particles suggests a severe underprediction (larger than a factor of 4) of PM(2.5) mobile emissions in the inventory. Analyses of ambient CO, NO(x) and CO/NO(x) concentration trends in the MCMA indicate that the early morning ambient CO/NO(x) 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 NO(x). These trends, together with the analysis of fuel sales and fleet size, suggest that the relative contribution of diesel vehicles to overall NO(x) 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 NO(x) 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.en
dc.description.sponsorshipUS Department of Energy's Atmospheric Sciences Program DE-FG02-05ER63980, DE-FG02-05ER63982en
dc.description.sponsorshipUS National Science Foundation's Atmospheric Chemistry Program ATM-0528170, ATM-528227en
dc.description.sponsorshipMexico's Comision Ambiental Metropolitanaen
dc.identifier.citationZavala, M., Herndon, S. C., Wood, E. C., Onasch, T. B., Knighton, W. B., Marr, L. C., Kolb, C. E., and Molina, L. T.: Evaluation of mobile emissions contributions to Mexico City's emissions inventory using on-road and cross-road emission measurements and ambient data, Atmos. Chem. Phys., 9, 6305-6317, doi:10.5194/acp-9-6305-2009, 2009.en
dc.publisherCopernicus Publicationsen
dc.rightsIn Copyrighten
dc.subjectMotor-vehicle emissionsen
dc.subjectMetropolitan areasen
dc.subjectMCMA-2003 campaignen
dc.subjectExhaust emissionsen
dc.subjectOzone productionen
dc.subjectNitrogen oxidesen
dc.subjectField campaignen
dc.subjectAir qualityen
dc.subjectMeteorology & atmospheric sciencesen
dc.titleEvaluation of mobile emissions contributions to Mexico City's emissions inventory using on-road and cross-road emission measurements and ambient dataen
dc.title.serialAtmospheric Chemistry and Physicsen
dc.typeArticle - Refereeden


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