HR: 13:55h
AN: A13I-02    [Abstracts]
TI: Eddy Covariance Flux Measurements of Pollutant Gases in the Mexico City Urban Area: a Useful Technique to Evaluate Emissions inventories
AU: * Velasco, E
EM: evelasco@mce2.org
AF: Molina Center for Energy & the Environment, La Jolla, La Jolla, CA 92037, United States
AU: Grivicke, R
AF: Laboratory for Atmospheric Research, Washington State University, Pullman, WA 99164- 2910, United States
AU: Pressley, S
EM: spressle@wsu.edu
AF: Laboratory for Atmospheric Research, Washington State University, Pullman, WA 99164- 2910, United States
AU: Allwine, G
AF: Laboratory for Atmospheric Research, Washington State University, Pullman, WA 99164- 2910, United States
AU: Jobson, T
EM: tjobson@wsu.edu
AF: Laboratory for Atmospheric Research, Washington State University, Pullman, WA 99164- 2910, United States
AU: Westberg, H
EM: westberg@wsu.edu
AF: Laboratory for Atmospheric Research, Washington State University, Pullman, WA 99164- 2910, United States
AU: Lamb, B
EM: blamb@wsu.edu
AF: Laboratory for Atmospheric Research, Washington State University, Pullman, WA 99164- 2910, United States
AU: Ramos, R
AF: SMA-GDF, Agricultura 21, Mexico City, 11800, Mexico
AU: Molina, L
AF: Molina Center for Energy & the Environment, La Jolla, La Jolla, CA 92037, United States
AB: Direct measurements of emissions of pollutant gases that include all major and minor emissions sources in urban areas are a missing requirement to improve and evaluate emissions inventories. The quality of an urban emissions inventory relies on the accuracy of the information of anthropogenic activities, which in many cases is not available, in particular in urban areas of developing countries. As part of the MCMA-2003 field campaign, we demonstrated the feasibility of using eddy covariance (EC) techniques coupled with fast-response sensors to measure fluxes of volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City. Those flux measurements demonstrated to be also a valuable tool to evaluate the emissions inventory used for air quality modeling. With the objective to confirm the representativeness of the 2003 flux measurements in terms of magnitude, composition and diurnal distribution, as well to evaluate the most recent emissions inventory, a second flux system was deployed in a different district of Mexico City during the 2006 MILAGRO field campaign. This system was located in a busy district surrounded by congested avenues close to the center of the city. In 2003 and 2006 fluxes of olefins and CO2 were measured by the EC technique using a Fast Isoprene Sensor calibrated with a propylene standard and an open path Infrared Gas Analyzer (IRGA), respectively. Fluxes of aromatic and oxygenated VOCs were analyzed by Proton Transfer Reaction-Mass Spectroscopy (PTR-MS) and the disjunct eddy covariance (DEC) technique. In 2006 the number of VOCs was extended using a disjunct eddy accumulation (DEA) system. This system collected whole air samples as function of the direction of the vertical wind component, and the samples were analyzed on site by gas chromatography / flame ionization detection (GC-FID). In both studies we found that the urban surface is a net source of CO2 and VOCs. The diurnal patterns were similar, but the 2006 fluxes showed higher magnitudes. This difference was due to the different characteristics of the monitored sites rather than an increment of the emissions over a 3-year period. The diurnal patterns of VOCs and CO2 fluxes were strongly related to vehicular traffic. Toluene and methanol fluxes also exhibited a strong influence from non-mobile sources; in particular the 2006 flux measurements were influenced on some days by the application of a resin to the sidewalks in the neighborhood near the flux tower. The fluxes of individual hydrocarbons measured by DEA showed good agreement with the fluxes measured by EC and DEC which demonstrates that the DEA method is valuable for flux measurements of additional individual species. Finally, the comparisons between the measured fluxes of VOCs and the emissions reported by the emissions inventory for the monitored sector of the city showed that these last were within the observed variability of the measured fluxes.
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting