Can you see air pollution?

Believe it or not, you can! But you have to know how to look.

A recent conversation with a user of the Houston Clean Air Network led me to the topic of today’s article, which begins with a seemingly simple question: Can you see air pollution?

The simple answer is yes, some air pollution is visible. But in order to understand what you are seeing, you have to learn a little bit more about air pollution.

Starting with a recent example: small particles in the air create what we call “haze.” Just this week members of Air Alliance Houston and the Sierra Club attended an EPA hearing in Austin regarding a newly proposed rule to address “regional haze” in our nation’s parks and wilderness areas. Excessive haze, caused by air pollutants such as sulfur dioxide (SO2), limits visibility in these scenic areas. Other examples of particulate pollution becoming visible have simpler names, like “smoke” and “dust.”

Ozone is also visible, as many longtime residents of Houston know. The picture accompanying this article shows ozone pollution in Houston visible as a milky orange cloud.* Ozone plumes form and move about a city like clouds. This movement isn’t visible to the naked eye, but the Houston Clean Air Network helps you visualize ozone plumes. For an example of a day from the recent past with several visible ozone plumes, click here.

Other pollutants are invisible, or nearly so. Carbon monoxide is colorless and odorless. So is natural gas. Many dangerous or hazardous chemicals such as benzene and butadiene are also impossible to see or smell. In order to protect us from exposure to these hazards, we often use tools such as chemical detectors (for carbon monoxide) or fragrant chemical additives (for natural gas). When you “smell” natural gas, you are actually smelling a pungent chemical additive known as methyl mercaptan.

There are other ways to “see” air pollution using technology. Infrared cameras make visible emissions of volatile organic compounds (including the benzene and butadiene mentioned above) that would otherwise go undetected. Companies use infrared cameras to detect so-called “fugitive leaks” from valves, flanges, and other potential fugitive sources. The largest facilities in Houston have more than a million of these potential fugitive sources. Infrared cameras are also used to see leaks at oil and gas drilling operations.

In the not-too-distant future, vast networks of sensors will allow us to “see” air pollution and other phenomena in exciting new ways. The Houston Clean Air Network is an early example of the promise of these sensor networks. As these technologies and their visualizations improve, we will begin to see air pollution in ways we can’t even imagine today.

*UPDATE: This description confuses the colors of ozone versus “smog.” For a clarification written by our Board Member Lucy Randel, visit