Thursday, August 11, 2011

What Does “Ozone Warning Day” Mean?

It’s summer time and there are many “Ozone Warning Days” that you might see communicated on the local news, on the radio, or even on highways. Since there is a lot of confusion around the term ozone, we wanted to explain the differences between the two types of ozone.

When the Environmental Protection Agency (EPA) says, ozone is "good up high, bad nearby" what the agency is referring to is Upper Ozone and Ground Level Ozone.

Upper Ozone - or stratospheric ozone, is a particularly active form of oxygen, which filters out much of the sun’s harmful ultraviolet radiation. This ozone layer surrounds the earth high up in the stratosphere. Some stories on stratospheric ozone wrongly advise against using aerosol products. Back in the 1970’s scientists discovered that chemicals called CFC’s (chlorofluorocarbons) were contributing to the depletion of the upper ozone, subsequently; CFCs were banned from consumer aerosol products in 1978, and US aerosol products have not contributed to ozone depletion for over 30 years.

Ground Level Ozone – or tropospheric ozone, is a component of “smog” and can be unhealthy for inhabitants when levels exceed EPA standards. Smog formation requires three ingredients:

1) Sunlight;

2) Nitrogen oxides, which come mostly from anthropogenic (man-made) sources such as automobile exhaust and power plants; and

3) Volatile organic compounds (VOCs), about half of which are naturally occurring and half man-made. "Volatile" means evaporating, and virtually anything that gives off an odor or quickly evaporates into the air is a source of VOCs.

According to the weather section on this chemical process is describe as such:

When you burn gasoline in a car, a truck, or even a gasoline lawn mower, the stuff coming out of the exhaust pipe includes nitrogen oxides, which are gases. Each nitrogen dioxide molecule is made of one atom of nitrogen and two atoms of oxygen. On a sunny day, air containing nitrogen dioxide turns into a chemistry experiment that's not confined to a test tube.

One of the things that happens is the nitrogen-dioxide sheds one of its oxygen atoms, becoming nitrogen oxide. You can think of single oxygen atoms being lonely and hyperactive (if you like to think of things like atoms in this way.) The single oxygen atoms combine with some of the air's molecular oxygen (consisting of two oxygen atoms), becoming ozone.

Some smog alerts wrongly advise against using consumer products such as aerosol products. The EPA estimates that of the major man-made sources of VOCs, 58 percent are from industrial facilities, 37 percent are from vehicle emissions and 5 percent are from consumer products. The portion of these consumer products packaged in aerosol containers accounts for only a fraction of the 5 percent, and that tiny portion is largely composed of the least reactive—or least smog- forming—type of VOCs.

So, on a hot, sunny day, those ozone warnings are alerting you that air quality may be low and also accurately encouraging you to limit the activities that contribute to worsening the air quality.

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