Upwards of four million trucks enter the U.S. each year through various southern port crossings in California, Arizona, New Mexico and Texas. Scientific studies at congested US-Mexico border crossings suggest that cross-border truck emissions are contributing to air pollution problems in border communities. Officials expect the problem to become increasingly severe and widespread when the North American Free Trade Agreement (NAFTA) is fully implemented. Signed in 1992, NAFTA calls for more open trade between the US and Mexico. Legal battles had put NAFTA on hold; but a Supreme Court decision in 2004 cleared the way for full implementation of the international treaty.
M. J. Bradley & Associates, working with the U.S. Environmental Protection Agency (EPA) and the Arizona Department of Environmental Quality (ADEQ), conducted a three-week pilot program to evaluate the exhaust emissions of trucks crossing the US-Mexico border at the Mariposa Port of Entry in Nogales, Arizona.
Several technologies were deployed to monitor emissions, including advanced remote sensing devices (RSDs) developed by Environmental Systems Products (ESP) and portable emissions monitors (PEMs). A PEMS is a suitcase sized unit that is loaded onto a truck and connected to the vehicle's exhaust system, logging emissions data as the truck is driven. RSD systems unobtrusively measure exhaust emissions on the road as motor vehicles pass through ultraviolet and infrared beams cast across a roadway. Emissions data were gathered from more than 15,000 crossings and over 1,600 unique trucks. This is the first time remote sensing technology has been used at any border crossing to study truck emissions.