More Progress in Reducing Toxic Air Pollutants in Houston

Texas Commission on Environmental Quality Removes A Texas City Neighborhood from the Air Pollutant Watch List

Houston’s ozone levels receive a lot of attention, but the Texas Commission on Environmental Quality (TCEQ) also monitors and assesses the risks of dozens of other air pollutants, some of which are considered toxic. These toxic chemicals can have a variety of negative effects on health, some of which are mild, but some of which can be quite serious if the concentrations are high enough and if the exposure lasts for a long time. To help them evaluate potential health risks, TCEQ has developed scientifically-based air monitoring comparison values (AMCVs). AMCV’s have been developed for short and long term health effects and for odor/nuisance effects such as eye irritation or nausea.

TCEQ performs monitoring and then compares the data to each AMCV for each chemical. If that evaluation shows that measured concentrations of a specific air toxic compound exceed its AMCV, the TCEQ places that area (defined by the known air emission sources of that chemical) on their Air Pollutant Watch List, and then works with local government, industry and neighborhood residents to develop an action plan to reduce the pollution to acceptable levels.

During mobile monitoring studies in 2000 and 2001, concentrations of propionaldehyde were detected above the odor-based AMCV downwind of a manufacturing facility in Texas City and therefore, it was placed on the Texas City Air Pollutant Watch List. The map below shows the affected neighborhood.

Map for Houston Air Quality

Although no odorous levels were detected during a 2004 mobile monitoring study, odorous levels were detected during a 2008 mobile monitoring study. In 2015, the odor-based AMCV for propionaldehyde was updated from 9 parts per billion (ppb) to 40 ppb to better reflect actual odor nuisance conditions rather than just the detection of the pollutant. The primary source of propionaldehyde emissions made permanent and enforceable improvements to its facility to reduce emissions and the potential for odor nuisance conditions. The facility also conducted an air monitoring study, and none of the measured air concentrations were above the current odor-based AMCV of 40 ppb. The highest concentration measured during the study was under 30 ppb. The TCEQ determined that the numerous improvements to the facility and the low levels measured during the study support the delisting of Texas City and propionaldehyde from the APWL.

TCEQ’s APWL operates statewide. TCEQ recently announced plans to remove neighborhoods in Dallas and Beaumont from the APWL because they had met health-based benchmarks.

What happens now? Businesses and industries must continue to keep their propionaldehyde emissions at the levels they agreed to as part of this process. TCEQ will continue to operate an air monitoring site in the area to ensure that measured concentrations of proprionaldehyde as well as other pollutants continue to stay below their respective AMCV. In addition, every year TCEQ scientists perform a comprehensive review of all data measurements of air toxics at every monitor across the state to ensure that they are within the most current AMCVs. Residents can be assured that TCEQ has a robust process to evaluate available monitoring data to ensure that it meets TCEQ’s health-based benchmarks.


TCEQ’s proposal provides more data and lists the measures that local businesses and industry took to reduce propionaldehyde levels. It’s available here: