Houston weather: What does Air Quality Alert mean? What's in the air?

HOUSTON - The Houston area is under an Air Quality Alert today, so what does that mean, and what exactly is in the air today? Well, it's complicated.

First off, on days like today with light winds and little cloud cover, sunshine can interact with pollutants called nitrogen oxides (abbreviated NOx). The sunlight can knock an oxygen atom off of the NOx and that atom bonds with regular oxygen that we all need for life to form O3, also known as ozone.

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Now, ozone is vital to our lives when it is very high in the sky because it blocks harmful ultraviolet light from harming our skin. However, it can be harmful when breathed in for extended periods, especially for people with lung conditions, children and senior citizens.

Here is a statement from the EPA on what to do when pollution levels are elevated:

"People with heart or lung disease, older adults, children and teens – take any of these steps to reduce your exposure:

 • Choose less strenuous activities (like walking instead of running) so you don’t breathe as hard.

 • Shorten the amount of time you are active outdoors.

 • Be active outdoors when air quality is better."

Ozone is invisible, but hazy skies today could be caused by a mixture of fine particles including smoke from forest fires in Canada, smoke from agricultural fires in Mexico, local pollution from vehicles and industry, and even pollen and plain old dust. These are all known as "particulate matter," and the same kinds of precautions mentioned above for ozone should be taken for high levels of particulate matter.

Maps from the Environmental Protection Agency show both a national and state view of smoke plumes from our north and south, so we do have a mixture of smoke not just here in Texas, but for much of the country.

Levels of air quality are broken down into five categories shown here ranging from green for good to purple for unsafe levels. Levels in Houston reached level orange this morning and will likely reach level red at times this afternoon.

The bottom line is that on days like today, it's all about how long you're outside and how deeply you're breathing, so it's best to avoid a long run or strenuous outdoor work until this evening when levels of pollution will begin to fall.