Trailblazing research from the University of Houston affirms air pollution levels in the San Antonio area can exceed federal limits, confirming measurements that over recent years have earned the city a U.S. Environmental Protection Agency non-attainment designation.
The Alamo City has company: Houston and Dallas are also challenged with meeting federal air quality standards. The researchers uncovered differing tales of air pollution among Texas' three largest urban areas – each involving its own sources and causes.
The San Antonio results are published in the journal Atmospheric Environment. Double breakthroughs fueled the team's latest work, which was funded by the Texas Commission on Environmental Quality.
"This was the first time we deployed our mobile air-quality laboratory to the San Antonio area," said Jimmy Flynn, research associate professor in the Department of Earth and Atmospheric Sciences in the UH College of Natural Science and Mathematics. Flynn is principal investigator for the multi-year Texas air-testing project, which brings together researchers from UH, Rice University and Aerodyne Research, Inc.
Flynn designed the mobile air-quality laboratory (MAQL) in 2013 to be the first mobile unit for UH with capacity for onsite processing of such large amounts of data over prolonged periods of time. As a result, daily comparisons can be made instantly and trends spotted while the team is still in the field.
"Most research will stop there and report the numbers," said researcher Fangzhou Guo.
New data analysis methods allow precise correlation of temperature, photochemistry and other factors in studying air pollution. On location in San Antonio, Fangzhou Guo (above, atop the team's mobile air-quality lab) and fellow researchers identified two specific challenges: Regional transport, which refers to pollution drifting in from elsewhere, and an abundance of ozone precursors.
The team turned to the second breakthrough, his analysis of integrating results from positive matrix factorization (PMF), a statistical algorithm used by environmental scientists, with location specific modeling to further pinpoint aerosol pollution rates and causes.
"My model shows correlations of aerosol formation rates with temperature, photochemistry and other driving forces. We believe this is the first time this has been done in the field," said Guo, first author of the Atmospheric Environment article on the San Antonio research. Guo is a former UH post-doctoral researcher and continues as an active member of the UH research team. He recently joined Aerodyne Research as senior scientist.
Ozone, one of six air pollutants designated by the EPA, has historically been the biggest challenge for San Antonio's air quality, and the city actually faces two problems in dealing with it. One is regional transport, referring to pollution not originating locally but drifting in from other parts of the state or across international borders. The second is an abundance of ozone precursors that can readily mix under certain photochemistry conditions and form ozone.
"One type is NOx, or nitrogen oxides. The other is volatile organic compounds, called VOCs. The same nitrogen oxides that can be produced by power plants can also come from vehicle emissions. Basically, everything that burns fossil fuels can produce NOx," Guo explained. "VOCs can be anthropogenic, such as pollutants from the oil and gas industry and our house-cleaning products and perfumes. Or they can be biogenic and come from trees."
Wildfires, such the recent massive ones in west Texas and elsewhere, compromise air quality, too.
"Burning biomass can produce both NOx and VOCs and also tons of particles. Bad for us, bad for climate," Guo said.
Adding to San Antonio's ozone trouble is the hot south Texas climate that gives the city a very long ozone season, from April until the end of September.
Most recently, the team has focused on atmospheric particulate matter.
"The smaller the particles, the easier they can penetrate into our lungs. Some are so small they even find their way into our blood vessels. Very fine particles can not only cause respiratory issues, but also be the root of some cardiovascular issues," Guo said.
To accurately test San Antonio air, the UH research team first located the mobile air-quality laboratory in an urban area just southeast of the downtown San Antonio Riverwalk, and later on the campus of The University of Texas at San Antonio on the city's northwest side.
The scientific team also included Rice University's Robert Griffin, now at Roger Williams University, and Baylor University's Rebecca Sheesley and Sascha Usenko.
The preparation of this work was financed through a contract from the State of Texas through the Texas Commission on Environmental Quality (TCEQ). The content, findings, opinions and conclusions are the work of the authors and do not necessarily represent findings, opinions, or conclusions of the TCEQ.
