Puget Sound Clean Air Agency

Photo: Agency Web cam shot of very hazy dayOzone

VOC + NOx + Sunlight = Ozone

Ozone is a pungent-smelling, colorless gas produced in the atmosphere when nitrogen oxides (NOx) and volatile organic compounds (VOC) chemically react under sunlight. The highest ozone levels occur on hot summer afternoons.

Good up high, bad nearby.

Upper atmosphere ozone protects the earth from harmful radiation, but ground-level ozone (commonly known as smog) is unhealthy. Exposure to ground-level ozone can reduce lung function, cause respiratory irritation, aggravate asthma symptoms, and weaken the immune system. Ozone has environmental impacts as well; studies show that ozone can damage agricultural crops and forests.

How is the ozone in our region?

In 2013, the U.S. Environmental Protection Agency may tighten the national ambient air quality standards for ozone. The revised standard would be more protective of public health. If the standard is lowered, it is likely that portions of the Puget Sound area would be determined to be in violation of the new standard.

What contributes to ozone?

The bulk of our ozone-causing nitrogen oxides and VOCs come from the transportation sector – emissions from cars and light trucks, marine vessels, and heavy-duty diesel vehicles. Other sources include gasoline refueling; industrial solvents; and auto-body paint shops, among others.

What can be done to reduce ozone?

With most ozone caused by emissions from our tailpipes, choices we make about what we drive, how often and far we drive, and the kind of fuel we use can make a difference.

For more on ozone: