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Published: 2008

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This project was one of three collaborating grants funded by DOE/ASP to characterize the fine particulate matter (PM) and secondary PM precursors in the Mexico City Metropolitan Area (MCMA) during the MILAGRO Campaign. The overall effort of MCMA-2006, one of the four components, focused on i) examination of the primary emissions of fine particles and precursor gases leading to photochemical production of atmospheric oxidants and secondary aerosol particles; ii) measurement and analysis of secondary oxidants and secondary fine PM production, with particular emphasis on secondary organic aerosol (SOA), and iii) evaluation of the photochemical and meteorological processes characteristic of the Mexico City Basin. The collaborative teams pursued the goals through three main tasks: i) analyses of fine PM and secondary PM precursor gaseous species data taken during the MCMA-2002/2003 campaigns and preparation of publications; ii) planning of the MILAGRO Campaign and deployment of the instrument around the MCMA; and iii) analysis of MCMA-2006 data and publication preparation. The measurement phase of the MILAGRO Campaign was successfully completed in March 2006 with excellent participation from the international scientific community and outstanding cooperation from the Mexican government agencies and institutions. The project reported here was led by the Massachusetts Institute of Technology/Molina Center for Energy and the Environment (MIT/MCE2) team and coordinated with DOE/ASP-funded collaborators at Aerodyne Research Inc., University of Colorado at Boulder and Montana State University. Currently 24 papers documenting the findings from this project have been published. The results from the project have improved significantly our understanding of the meteorological and photochemical processes contributing to the formation of ozone, secondary aerosols and other pollutants. Key findings from the MCMA-2003 include a vastly improved speciated emissions inventory from on-road vehicles: the MCMA motor vehicles produce abundant amounts of primary PM, elemental carbon, particle-bound polycyclic aromatic hydrocarbons, carbon monoxide and a wide range of air toxics; the feasibility of using eddy covariance techniques to measure fluxes of volatile organic compounds in an urban core and a valuable tool for validating local emissions inventory; a much better understanding of the sources and atmospheric loadings of volatile organic compounds; the first spectroscopic detection of glyoxal in the atmosphere; a unique analysis of the high fraction of ambient formaldehyde from primary emission sources; characterization of ozone formation and its sensitivity to VOCs and NOx; a much more extensive knowledge of the composition, size distribution and atmospheric mass loadings of both primary and secondary fine PM, including the fact that the rate of MCMA SOA production greatly exceeded that predicted by current atmospheric models; evaluations of significant errors that can arise from standard air quality monitors for O3 and NO2; and the implementation of an innovative Markov Chain Monte Carlo method for inorganic aerosol modeling as a powerful tool to analyze aerosol data and predict gas phase concentrations where these are unavailable. During the MILAGRO Campaign the collaborative team utilized a combination of central fixed sites and a mobile laboratory deployed throughout the MCMA to representative urban and boundary sites to measure trace gases and fine particles. Analysis of the extensive 2006 data sets has confirmed the key findings from MCMA-2002/2003; additionally MCMA-2006 provided more detailed gas and aerosol chemistry and wider regional scale coverage. Key results include an updated 2006 emissions inventory; extension of the flux system to measure fluxes of fine particles; better understanding of the sources and apportionment of aerosols, including contribution from biomass burning and industrial sources; a comprehensive evaluation of metal containing particles in a complex urban environment; identification of a close correlation between the rate of production of SOA and "Odd Oxygen" (O3 + NO3) and primary organic PM with CO in the urban plume; a more sophisticated understanding of the relationship between ozone formation and ozone precursors: while ozone production in the urban area is VOC-limited, the response is mostly NOx-limited in the surrounding mountain. Comparison of the findings from 2003 and 2006 also confirm that the VOC levels have decreased during the three-year period, while NOx levels remain the same. The results from the 2002/2003 and 2006 have been presented at international conferences and communicated to Mexican government officials. In addition, a large number of graduate students and post-doctoral associates were involved in the project. All data sets and publications are available to the scientific community.