San Antonio’s air quality problems stem from a combination of intense heat, vehicle emissions, industrial pollution, and regional sources that push ozone and particulate matter to unhealthy levels. Bexar County carries a “Serious” nonattainment designation from the EPA for ground-level ozone, meaning it consistently fails to meet federal air quality standards. The city’s geography, climate, and proximity to one of the largest oil and gas fields in the country all work against it.
Ground-Level Ozone Is the Core Problem
Ozone is the pollutant that drives most of San Antonio’s bad air quality days. Unlike the ozone layer high in the atmosphere, ground-level ozone forms when emissions from cars, trucks, power plants, and industrial facilities react with sunlight. San Antonio gets an enormous amount of both: heavy traffic from a sprawling metro area of over 1.7 million people and some of the most intense sunshine in the country.
The relationship between heat and ozone is direct and measurable. Modeling studies have found that a single degree Celsius increase in temperature can raise peak ozone concentrations by about 5.3 parts per billion, roughly an 11% jump. San Antonio regularly sees stretches of 100-degree days through the summer, creating ideal conditions for ozone to build up day after day. When the Texas Commission on Environmental Quality forecasts that ozone will push the Air Quality Index above 100 into the “Unhealthy for Sensitive Groups” range, the region issues an Ozone Action Day alert. These alerts are common from May through October.
Eagle Ford Shale Emissions Drift Into the City
San Antonio sits roughly 60 miles north of the Eagle Ford Shale, one of the most productive oil and gas regions in the United States. Drilling, fracking, and processing operations across the field release a cocktail of pollutants that don’t stay in the rural counties where they originate.
Research published in Atmospheric Environment found that unconventional oil and gas development in the Eagle Ford produces elevated levels of nitrogen oxides, ozone, fine particulate matter, hydrogen sulfide, and a wide range of volatile organic compounds. These include both the lighter hydrocarbons typically measured by standard monitoring equipment and larger, heavier hydrocarbons that often go unquantified but still exist at substantial concentrations. Some of the compounds detected, including benzene, are toxic and carcinogenic. Nitrogen oxides from these operations are especially problematic because they serve as a key ingredient in ground-level ozone formation once they reach a sun-drenched metro area like San Antonio.
Cement Plants and Local Industry
San Antonio is home to major industrial point sources, including the Alamo Cement Plant on the city’s northeast side. In 2023, this single facility reported roughly 787,000 metric tons of carbon dioxide equivalent emissions. Cement manufacturing is one of the most emissions-intensive industrial processes, releasing CO2 from both burning fuel and the chemical breakdown of limestone. The plant also produces nitrogen oxides and fine particulate matter as byproducts of its high-temperature kilns.
The cement plant’s location within the metro area means its emissions mix directly into the air residents breathe, rather than dispersing over unpopulated land. On still, hot days when air stagnates over the city, these industrial emissions compound the ozone and particulate levels already elevated by traffic and regional sources.
Smoke From Mexico and Saharan Dust
San Antonio’s air quality takes seasonal hits from sources hundreds or even thousands of miles away. Each spring, large-scale agricultural burning across Mexico and Central America sends plumes of smoke northward across the Gulf of Mexico. Southeasterly Gulf winds push that smoke directly into central Texas, creating the thick haze that often blankets the city from April through June. Hundreds of fires burn simultaneously during peak season, and the residual smoke can travel vast distances before settling over the region.
Later in summer, Saharan dust clouds cross the Atlantic and occasionally reach Texas. These events spike fine particulate levels and give the sky a milky, washed-out appearance. While each individual event is temporary, lasting a few days to a week, the cumulative effect during spring and summer means San Antonio rarely gets a break from poor air quality during its hottest months.
A Sprawling City Built for Driving
San Antonio is one of the most car-dependent major cities in the country. The metro area stretches across more than 500 square miles, public transit options are limited compared to similarly sized cities, and highways like I-35, I-10, and Loop 1604 carry heavy traffic volumes throughout the day. Vehicle exhaust is the single largest source of nitrogen oxides and volatile organic compounds in the region, both of which are precursors to ozone.
Unlike coastal cities that benefit from consistent ocean breezes pushing pollution out, San Antonio sits inland on relatively flat terrain. Temperature inversions, where a layer of warm air traps cooler air near the surface, can lock pollutants close to the ground for hours or days at a time. The city’s rapid population growth, which has added hundreds of thousands of residents over the past two decades, means more vehicles, more construction dust, and more emissions from energy generation with each passing year.
What the EPA Designation Means
The EPA’s “Serious” nonattainment classification for Bexar County isn’t just a label. It triggers stricter regulatory requirements for new industrial permits, emissions offsets, and pollution control technologies. It also means the region has failed to meet the 2015 ozone standard despite years of effort. Moving from “Serious” to an even worse classification would bring additional federal restrictions on development and industry.
For residents, the practical impact shows up on high-ozone days when children, older adults, and anyone with asthma or heart disease faces real health risks from spending time outdoors. Ozone irritates the airways, reduces lung function, and can trigger asthma attacks even in people whose condition is normally well controlled. On days when the AQI climbs into the orange range (101 to 150) or higher, limiting outdoor exercise during afternoon hours, typically between noon and 7 p.m., makes a measurable difference in exposure.