Air Quality in Houston

Ozone, particle pollution and toxic waste releases contribute to poor air quality in urban areas

While improvements are being made, the Houston area — particularly Harris County — still suffers from higher-than-average levels of air pollution.

Why air quality matters to Houston

In the 1990s, Houston was deemed the nation’s smog capital. Despite significant efforts to reduce air pollution over the past two decades, ozone levels caused by growing industries, heavy traffic and a car-dependent culture remain a persistent problem for the Houston region. According to a new “State of the Air” report, Houston ranked 9th in the nation for ozone pollution, and particle pollution levels remain higher than the state and national averages.1 High levels of ozone and particle population have been found to lead to premature death and other health conditions like lung cancer, asthma attacks, cardiovascular damage, and developmental and reproductive damage.2 Across the U.S., about 50,000–100,000 excess deaths occur due to air pollution.3 Committing to a reduction of these emissions and complying with federal air quality standards are vital ways of ensuring a healthy air quality for the Houston region.

The more we know about air quality concerns in the Houston area, the better equipped we are to take informed action toward healthier communities.

The data

Though improving, high ozone levels still undermine public health in the Houston area

Ground-level ozone is a big component of smog and a harmful pollutant that can cause many health problems, including a variety of respiratory diseases and damage to the environment. Given how dangerous ozone levels are for vulnerable populations, including children and seniors, the Texas Commission on Environmental Quality (TCEQ) posts readings on current ozone levels for Houston metropolitan area.4 Currently, the National Ambient Air Quality Standards for ground-level ozone are set at 70 parts per billion (ppb) averaged over an 8-hour period.5

Between 2010 and 2016, the number of days in which ozone levels were above EPA standards dropped from 34 days to 17 days, or by 50% in Harris County, and from 6 days to 4 days, or by a third in Montgomery County, according to the actual monitor readings.

Ozone is most likely to reach unhealthy levels on hot days in urban areas, though it can also reach high levels during the colder months. Typically the ozone readings reach the highest values between April and September in the region.

Since 2000, the ground-level ozone levels in Texas dropped by 28%, which is twice the national average rate, according to the TCEQ. Houston’s air quality is improving at the same pace as the state.

However, the Houston area still doesn’t meet EPA ozone standards, and decreases have largely leveled off. In 2018, EPA gave Houston three years to meet health-based limits for ground-level ozone. Because ozone can be transported long distances by wind, collaborative efforts across the counties are indeed needed to tackle this issue and meet the deadline.

28% ground-level ozone reduction

Since 2000, Texas has reduced ozone levels at twice the national rate.

Reducing particle pollution represents a valuable opportunity for Houston air quality

Particulate matters are small particles that, due to microscopic size, are easily inhalable by humans causing a variety of cardiovascular and respiratory diseases. Vulnerable populations including children and older adults have higher chances of being affected. These particles are released into the air by different industrial processes, fires, dust, or formed from vehicle exhaust. These particles are collectively referred to as PM2.5 due to their 2.5-micrometer diameter.

PM2.5 in Texas has decreased by 24% for both 24-hour PM2.5 and annual PM2.5 between 2002 and 2017, according to TCEQ.

According to CDC data, the annual average ambient concentration of PM2.5 in micrograms per cubic meter (μg/m3) in Harris County is at the same level as the national average in 2014. Both Fort Bend and Montgomery counties had lower PM2.5 ambient concentrations compared to the national average.

Although PM2.5 levels have decreased in the three-county area between 2014 and 2018, we didn’t keep up with the national trend.

“According to EPA data, all three counties have higher annual averages of PM2.5 concentration than the state and the national averages as of 2018.”

Toxic chemicals released to air

As part of waste management process, some chemicals are released into the air. The EPA’s Toxics Release Inventory (TRI) program tracks the amount of chemicals released by environmental medium in Harris, Fort Bend and Montgomery counties from 2003-2017.6

In 2017, one-third of industrial releases of TRI-monitored chemicals in Harris County were released to the air. In comparison, 24% of toxic chemicals in Fort Bend County and 100% in Montgomery County were released to the air, though the amount is considerably smaller than that in Harris County.

All three counties lowered the total amount of air releases over time. Even with declines, though, Harris County significantly surpasses both Fort Bend and Montgomery counties with an annual average of almost 12 million pounds of chemicals released into the air in the past decade.



  1. American Lung Association. “State of the Air 2019,” American Lung Association (2019).
  2. U.S. Environmental Protection Agency, “Ground-level Ozone Pollution,” last modified June 11, 2019.
  3. U.S. Environmental Protection Agency, Air Quality Criteria For Ozone And Related Photochemical Oxidants (Final Report, 2006), by the U.S. Environmental Protection Agency (EPA/600/R-05/004aF-cF), Washington, DC, 2006. Web.
  4. Texas Commission on Environmental Quality, “Current Ozone 1-Hour Levels for Houston Metropolitan Area (map).”
  5. U.S. Environmental Protection Agency, “2015 Revision to 2008 Ozone National Ambient Air Quality Standards (NAAQS) Related Documents,” last modified March 29, 2018.
  6. Toxics Release Inventory Program, “TRI for Communities,” U.S. Environmental Protection Agency, last modified September 19, 2019.