This award will support studies of organic and other aerosols and their regional impact through the integration of modeling studies with the extensive multi-platform ground-, aircraft- and satellite-based measurements obtained during the 2006 MILAGRO (Megacity Initiative: Local And Global Research Observations) Campaign in the Mexico City Metropolitan Area. An updated comprehensive measurement-based emissions inventory of gases and particulate matter (PM) will be developed and will be used as input to chemical transport models. In turn, the capability of the chemical transport models to reproduce the rich MILAGRO PM and trace gas data sets will be evaluated. Chemical transport modeling studies will be conducted using a modified version of an on-line coupled Weather Research Forecasting Model with Chemistry (WRF-CHEM). A meteorological ensemble technique will be used to investigate the meteorological impacts on PM simulations. The project will address five specific objectives: i) to improve the estimates of gaseous and PM emissions and the meteorological fields; ii) to characterize formation of secondary organic aerosol (SOA) from different emission sources; iii) to assess the impact of biomass burning and biogenic sources on PM; iv) to quantify the relative contribution of anthropogenic vs. natural sources of PM on the regional scale; and v) to investigate the impact of urban aerosols on regional photochemistry and meteorology.

The project will provide support for postdoctoral researchers. The results of this study will be of value to the scientific community, but also be used in presentations to Mexican authorities interested in regional air quality.

Project Report

The overall goal of this project is to contribute to the characterization of organic aerosol (OA) and its regional impacts through the integration of modeling studies with the extensive multi-platform ground-, aircraft- and satellite-based measurements obtained during the 2006 MILAGRO (Megacity Initiative: Local and Global Research Observations) Campaign in the Mexico City Metropolitan Area (MCMA). Airborne particulate matter, emitted and/or formed from a wide variety of anthropogenic and natural sources, such as biomass burning, has a wide range of impacts, from damaging human health and visibility to altering the earth’s climate. Results from this project have contributed to current knowledge on the sources and evolution of organic aerosols and shed some light on the effects of aerosols on regional air quality and climate, two of the most important environmental challenges facing policy makers today, especially in fast growing megacities such as Mexico City. They have helped to identify different emissions sources of organic aerosols and assess their impact on regional meteorology and photochemistry, evaluate the source contributions to fine particle concentrations, as well as provide a rigorous evaluation of emissions estimates and transport in the air quality models. A comprehensive measurement-constrained emissions inventory of gases and particulate matter (PM) has been developed from the extensive multi-platform measurements obtained during the 2006 MILAGRO Campaign in the MCMA. This comprehensive emissions inventory has been used as input to the chemical transport models (CTMs) and has improved the model results by reducing the uncertainties in the emissions. Modeling study demonstrates that uncertainties in meteorological initial conditions have significant impacts on SOA simulations, including the peak time concentrations, the horizontal distributions, and the temporal variations. The meteorological ensemble is possibly an efficient method in reducing the meteorological uncertainties in simulations of CTMs. The modeling results suggest that in the MCMA and surrounding region, biomass burning is a major contributor to primary OA (POA) and an important source to SOA and elemental carbon (EC), in contrast to its negligible effects on ozone formation. Garbage burning makes important contribution to OA and EC in the MCMA, despite its substantially lower PM emissions compared to open fires. Garbage burning is also a major source for particulate chloride and HCl, with the latter caused by the burning of polyvinyl chloride (PVC). The results suggest that garbage burning poses a serious health risk to the residents of Mexico City. Impacts of different emissions sources on organic aerosols in the MCMA have been characterized, and the relative contributions of anthropogenic and natural sources to the PM concentrations have been evaluated. Fossil fuel and biomass burning are the dominant sources for OA, and PM2.5 is generally evenly split between inorganic and carbonaceous aerosols. Simulations of urban-regional emissions interactions indicate that regional emissions and regional background exert an important contribution to the maximum O3 concentrations in the MCMA, while the MCMA emissions have limited effects on regional maximum O3. The impacts of urban emissions on carbonaceous aerosols are generally confined to the local areas, and the regional emissions exert limited influences on the urban aerosols. Furthermore, external industrial sources can influence the air quality in the MCMA. It is important to strengthen regional air quality monitoring and emissions characterization. Parameterization of HONO sources has been developed based on available laboratory experiments and field observations, and considering six HONO formation mechanisms. This parameterization can serves as an indirect evaluation of the emission of semivolatile organics and better understanding of the impacts of HONO sources on the formation and evolution of SOA. Aerosols decrease substantially the incoming solar radiation and reduce the surface temperature in Mexico City and daytime daytime Planetary Boundary Layer height. The aerosol’s radiative effects generally increase the surface concentrations of primary species, but do not significantly perturb the surface concentrations of the secondary species. Furthermore, when convective events occur in the city, the aerosol radiative effects reduce the convective available potential energy and the convective precipitation. Documented findings from this project have been presented at international conferences and published in peer-reviewed journals. All data and results from this project are available to the scientific community. Key findings and policy implications have been communicated to relevant Mexican officials and stakeholders. Several postdoctoral researchers were involved in all aspects of the project activities, co-authored appropriate manuscripts and reports, participated in seminars, meetings, workshops, and proposal development, as part of their education and training on global change research. The project also provided opportunity for the post-docs and research scientists to interact with students and researchers from US, Mexico and other international institutions as well as with Mexican government officials, thus enriching their research activities and raising awareness on environmental issues.

National Science Foundation (NSF)
Division of Atmospheric and Geospace Sciences (AGS)
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Sylvia A. Edgerton
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Molina Center for Strategic Studies in Energy & the Environment
La Jolla
United States
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