Whether you’re a novice or an expert, we’d like to talk to you about air pollution, its causes, and what we can do about it together. Below are some examples of pollutants that threaten our health in Houston.


Ozone, or smog, is a dangerous pollutant that poses a serious threat to human health. It is not emitted directly into the air, but rather is created through a chemical reaction. Nitrogen oxides (NOx) and volatile organic compounds (VOCs) combine in the air and are heated by the sun to form ozone.

Sources of NOx and VOCs include: petrochemical refineries, chemical plants, construction equipment, power plants, breweries, restaurants and bakeries, dry cleaners, marine vessels, planes, trains and automobiles. And yes: trees and plants also emit some of these chemicals.

In Houston, weather conditions are often perfect for the formation of ozone. Ozone is formed on warm, sunny days with little to no wind and no rain. The sea breeze coming from the Gulf of Mexico moves ozone pollution around the Houston region. Early morning winds come from the Northwest carrying pollution from the Houston Ship Channel (where large concentrations of NOx and VOCs have been measured) and push these pollutants out to sea. When the afternoon temperature heats up, the winds switch direction and move clockwise, carrying pollution north of the city. The Texas Commission on Environmental Quality (TCEQ) has measured high ozone levels in areas like Fort Bend County.

Particulate Matter

Our page on particulate matter is available here.


Air toxics are hazardous air pollutants that have a serious negative impact on human health, like causing cancer, reproductive effects or birth defects.

The U.S. Congress amended the Clean Air Act In 1990 to allow the Environmental Protection Agency (EPA) to oversee the control of 188 hazardous air pollutants (HAPs) in order to protect human health. The EPA works with local and state governments to implement technologies that control the emission of these chemicals.

Because Houston is home to many of the largest petrochemical facilities in the U.S. and the world, Houston unfortunately has many different HAPs in our air. Of the EPA’s 188 HAPs, 161 are present in varying concentrations at different locations in the Houston area.

Air toxics like 1,3-butadiene, used to produce different kinds of rubber products such as tires, and benzene, found in gasoline, can reach annual levels many times higher than in other major U.S. cities, according to a 2006 study by Rice University.

Communities that are most at risk of developing health effects from air toxics are the neighborhoods located in close proximity to petrochemical plants and refineries. These areas are called fenceline communities because they are literally in the backyard of some major industrial facilities. The Manchester community located in Houston’s East End is one of these fenceline communities.

Air Alliance Houston is working with local elected officials and regulatory agencies, as well as other environmental groups, to promote new technologies that can be implemented to significantly reduce the harmful emissions of air toxics.

For more information, visit Toxic Texas.

Educational videos on air pollution and health are available from AIRNow.gov.