ERG Helps Air Quality Improvement Efforts in Imperial County, California, by Characterizing Mexico Emissions

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Alongside the California Air Resources Board (CARB), ERG has played an important role in addressing air quality issues in Imperial County, an area in southeastern California that has long struggled to meet federal standards for ozone and fine dust. Historically, much of the pollution contributing to Imperial County’s nonattainment status has been traced to Mexico, specifically from the urban regions of Mexicali and northern Baja California. To better understand how Mexico’s emissions are affecting air quality in this area of California, CARB contracted ERG to study emissions in Mexico and analyze the types of motor vehicles operating near the California–Mexico border. 

Leveraging nearly three decades of experience with developing and reviewing Mexico emissions inventories, ERG conducted a thorough review of the 2014 Mexico National Emissions Inventory (MNEI) for the State of Baja California. The 2014 MNEI was developed by Mexico’s Secretariat of Environment and Natural Resources and quantifies emissions for the 2014 calendar year at the municipality level for each of the 32 Mexican states. This review was further supplemented by a weeklong site visit to Mexicali, where ERG team members collected on-the-ground data for key nonpoint sources, including border crossings, agricultural burning, brick kilns, and windblown dust. Based on these findings, ERG made significant technical improvements to the 2014 MNEI data, resulting in a more accurate portrayal of Baja California’s contributions to cross-border air quality issues. 

“During our Mexicali site visit, we saw various Mexico-specific emission sources that do not have analogous counterparts in the U.S., like border crossings with long waiting times; agricultural burning used as an asparagus cultivation practice; and small-scale brick kilns firing with coconut husks, pallet wood, and other scrap biomass,” said ERG Senior Air Quality Engineer Marty Wolf. “Viewing these emission activities in person, along with conducting interviews, allowed us to obtain more detailed local information that improved the quality of our emissions estimates rather than force-fitting U.S.-based estimation methods to Mexico-specific emission sources.”  

Additionally, CARB tasked ERG with providing a high-quality characterization of vehicles operating near the border, as they are a major source of emissions in this region. ERG applied its expertise in developing the MOVES-Mexico model and utilized advanced remote sensing technology, including license plate recognition and vehicle emission measurements, in the Baja California cities of Tijuana, Mexicali, and Tecate. Remote sensing measures tailpipe exhaust emissions from vehicles by sending narrow beams of infrared and ultraviolet light across the roadway to a mirror which then reflects the light back to detectors which measure the amount of transmitted light at characteristic wavelengths absorbed by various pollutants.  

The findings revealed that unregistered vehicles with high emissions levels are a significant contributor to pollution in the border area, underscoring the need for targeted mitigation efforts. 

By accurately characterizing cross-border emissions and the impact of high-emitting vehicles, ERG has provided CARB with tools needed to develop informed, evidence-based air quality management strategies. Ultimately, this work helps safeguard the health of residents in Imperial County while contributing to broader efforts to reduce cross-border pollution and improve air quality in both the U.S. and Mexico. 

For more information about the services our air quality experts provide, visit https://www.erg.com/service/air-quality.

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