Drive Clean Texas

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Knowing the kinds of pollutants and their effects is just one way you can arm yourself with information to stay safe and keep Texas air clean.


Ozone is necessary for life on earth. In its proper place in the stratosphere, ozone helps protect the earth from the sun's harmful rays. But on the earth's surface, ozone is the major ingredient of smog.

Ground-level ozone is not emitted directly into the air, but is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) come together in the presence of sunlight. Both NOx and VOCs are found in the exhaust from motor vehicles and other sources of combustion or industrial processes. VOCs also come from living sources or biological processes.

Summer days in Texas can be conducive for ozone formation. Sound science and regulations have greatly reduced ozone in Texas cities and ozone concentrations have decreased statewide— by 29% from 2000 to 2014.

What are the health effects of ground-level ozone?

Breathing relatively high levels of ground-level ozone can cause decreased lung function and pain with deep breaths. It can also aggravate the symptoms of asthma.

Sources: TCEQ & EPA

Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless, poisonous gas. It results from something being burned, and an improperly tuned vehicle engine is likely to have higher carbon monoxide emissions. Nationwide, about 60 percent of CO emissions come from motor vehicle exhaust, while in urban areas the percentage of CO emissions produced by cars and trucks increases to 95 percent.

What are the health effects of carbon monoxide?

Carbon monoxide can cause harmful health effects by reducing oxygen delivery to the body's organs (like the heart and brain) and tissues. At extremely high levels, CO can cause death.

Sources: EPA & AIRNow

Sulfur Dioxide

Sulfur dioxide (SO2) is one of a group of highly reactive gases called sulfur oxides (SOX). The largest source of SO2 emissions is fossil fuel combustion at power plants and other industrial facilities.

What are the health effects of sulfur dioxide?

Exposure to SO2 can affect the respiratory system, especially for people with asthma. Studies show connections between short-term exposure and increased visits to emergency departments and hospital admissions for respiratory illnesses, particularly for higher risk populations including children, the elderly, and people with asthma.

Sources: TCEQ

Nitrogen Oxides

The sum of nitric oxide (NO) and nitrogen dioxide (NO2) is commonly called nitrogen oxides (NOx). Other compounds, including nitrous acid and nitric acid, are part of the NOx family. NO2 is the component of greatest interest and the indicator for the larger group of NOx. NO2 forms quickly from emissions from cars, trucks, and buses; power plants; and off-road equipment.

What are the health effects of nitrogen dioxide?

Exposure to NO2 is associated with a number of adverse effects on the respiratory system, especially for people with asthma.

Sources: TCEQ

Particulate Matter

Particulate matter (PM) is a mix of small particles and liquid droplets. These particles can be made up of acids, organic chemicals, metal, dust, or soil.

Particulates are different in several ways including size:

By comparison, the average diameter of human hair is 70 micrometers.

What are the health effects of particulate matter?

Small particles less than 2.5 micrometers in diameter can be inhaled deeper into the lungs. Scientific studies have linked exposure to high concentrations of some types of PM with a variety of problems, including:

These associations are much less certain at concentrations below the current standard set by the EPA for PM in ambient air.

Sources: TCEQ