Air pollution continues to be an increasing problem in the largest metropolitan areas and regional industrial and commercial corridors of Mexico. Current air quality trends in Mexico (INE 1999, 2000) indicate that urban centers like Mexico City, Monterrey, Guadalajara, Toluca, Ciudad Juarez, Mexicali and Tijuana continue to exceed the Mexican Air Quality Standards for ozone and PM 10, while other cities are starting to show warning signs of future air quality problems. PM 2.5 monitors are just starting to be deployed in these cities, thus no data is available on this pollutant.

For some time now, it has been acknowledged that air quality problems are not exclusive of a limited area comprising only urban centers. Given the right conditions, pollutants can be transported hundreds of kilometers from their point of origin, and in the process new secondary pollutants can be formed. Of particular interest is the border region between Mexico and the United States where increasing commercial and industrial activities have originated common environmental problems in the two countries, including air pollution (INE 2000). Transboundary air pollution between the United States and Mexico has received increasing attention from both countries since the late 1970’s. A number of binational cooperative programs to study this problem have been signed in the past taking as basis, most notably, the “1983 La Paz Agreement on Cooperation for the Protection and Improvement of the Environment in the Border Area”. Recently, the United States Environmental Protection Agency (US EPA) and the Mexican Secretariat of Environment and Natural Resources (SEMARNAT) have launched the draft proposal for the Border 2012 US-Mexico Environmental Program. This program also sets its basis on the La Paz Agreement, and has established as its Goal #2 to reduce air pollution in the region. The border region, as defined by the La Paz Agreement, extends approximately 2,000 miles from the Gulf of Mexico to the Pacific Ocean, and 100 kilometers on either side of the international borderline. The region has experienced a dramatic population growth, which is linked to an important increase in the region’s industrial, economic and commercial activities. The importance of the region has also increased due to the passage of the North American Free Trade Agreement (NAFTA) in the mid-1990s. However, this socio-economic and industrial growth has brought environmental problems on both sides of the border.

Transboundary air pollution has been studied in different levels in different areas of the border region. Three main areas can be identified as the ones that have drawn most of the attention. The first area is the Lower California Area: Tijuana-San Diego/Mexicali-Calexico/Imperial Valley (e.g., Eatough et al., 1997; Chow et al., 2000; Pai et al., 2000). Here, most of the attention has been on primary particulate matter, with some studies addressing secondary pollutants. The second area is the airshed formed by Ciudad Juarez-El Paso-Sunland Park. Perhaps, this area is the one that has received most of the attention regarding transboundary air pollution and in a more comprehensive fashion. The 1996 Paso del Norte Ozone Study has lead the way to other studies, which have focus in recent years to study the dynamics of PM in the region (e.g., Roberts et al., 1997; Parson and Fitzgerald, 2001). The Lower Rio Grande area is, perhaps, the one that has received less attention, though different studies have raised the issue of transboundary air pollution in the region (e.g. Mejia-Velazquez and Rodriguez-Gallegos, 1997; Mukerjee, 1999; Gebhart, 2000; Mendoza-Dominguez et al., 2000a).

Given the air quality problems that, in particular, Mexicali and Calexico face, the Border Ozone Reduction and Air Quality Improvement Program for the Mexicali-Calexico region was established. The Program has as its objectives to “examine effective, scientifically based and measurable methods to reduce ozone creation and improve air quality along the border region of Imperial County, California and Mexicali, Baja California.” One of the specific objectives of the Program is to “review available data and assess current air quality in the border region, ensuring that any information gaps are filled”. The Instituto Tecnologico y de Estudios Superiores de Monterrey (ITESM) through the Air Quality Laboratory of the Center for Environmental Quality proposes to lead the research needed to comply with the objectives set forth by the Program. We have put together a research team that has vast experience in conducting similar projects.

We will center our attention in the Mexicali-Imperial Valley area to understand the air pollution dynamics between the United States and Mexico in that area. However, we will also expand our attention outside the Mexicali and Imperial Valleys to track down pollutant transport from major urban centers and point sources outside the area, but close enough to impact the air quality of the Valley (for example, Tijuana in Mexico and Los Angeles in the U.S.).

ITESM, with the Georgia Institute of Technology ( Atlanta, GA), studied in the past gas-phase pollutant dynamics in a region that included the border between Mexico and Texas using complex three-dimensional chemistry-transport models (e.g., Mendoza-Dominguez and Russell, 2000b). Those studies focused on emissions characterization of ozone precursors, air pollution data analysis and modeling of ozone dynamics in the region, including the application of direct sensitivity analysis techniques. Figure 1 (next page) presents some results obtained from those studies. Acting as continuing partners, we pretend to apply our capabilities to describe pollutant formation and transport around the Mexicali-Imperial Valley Border Area, including particulate matter and air toxics in our analyses. The expected results will include a better understanding of source-receptor relationships and source attribution in the region.

To complement the modeling effort, an observational program will be devised to improve our understanding of main sources of air pollutants in the region. This program will be designed and operated in a joint effort between ITESM and Aerodyne Research, Inc. (ARI) to complement past and current monitoring efforts in the region (including the routine monitoring network). Aerodyne’s mobile laboratory will be used to characterize pollutant emissions from mobile and stationary sources, as well as to get a better characterization of the chemical conditions of the atmosphere in the Mexicali and Imperial Valleys during specific time periods. Again the attention will be centered on ozone and particulate matter and their precursors, and air toxics. An effort is underway to bring additional funding to the project to deploy ambient air monitors to complement the mobile lab effort. In particular, there might be a need to enhance the spatial and temporal resolution of PM 2.5 (including speciation) and air toxics ambient data. If the resources are available, this will provide additional needed information for the air quality analysis and modeling efforts.

Figure 1. Air quality modeling results from past studies conducted by the Mexican PI in collaboration with Georgia Tech partners (Mendoza-Dominguez and Russell, 2000a). From left to right, and top to bottom: modeling domain, isoprene biogenic emissions estimates, maximum daily ozone field, and ozone sensitivity to mobile source NO x emissions.