What's Wrong with Our Air?
Ozone - Good Up High, Bad Nearby

The word "ozone" has prompted confusion and debate over the past few years. This confusion persists in part because ozone conjures up both good and bad images. In fact, both perceptions are correct.

This invisible gas can be found in both the upper and lower atmospheres. The ozone layer in the upper atmosphere exists naturally and is essential to life because it filters harmful ultraviolet radiation from the sun, reducing the amount reaching the earth's surface. High concentrations of ozone near ground level, however, can be harmful to people, animals, crops, and other materials.  Click here to learn more about the environmental impacts of surface ozone.

Unfortunately, ground-level ozone dissipates before it reaches the upper atmosphere where it could help filter the sun's harmful rays.

Ozone Basics

Ground-level ozone is the main ingredient in urban and regional smog. It is created when air pollutants from a variety of sources react in sunlight.

The main ozone-causing pollutants are volatile organic compounds (VOCs) and nitrogen oxides (NOx). Because heat and sunlight are also important factors in ground-level ozone formation, ozone pollution is primarily a concern from May through November.  To learn more about how ozone is formed, click here.

Motor vehicles account for about 30-40% of the ozone-causing pollutants in the Baltimore and Washington areas, but other sources include lawnmowers, boats, many household products, power plants, and industrial facilities.

Ozone Facts

• Ozone is an invisible gas. It is a highly reactive form of oxygen with three atoms (O3) instead of two (O2).
• Ozone is a secondary pollutant in that it is not emitted directly from any source but forms in the atmosphere.
• When left to its own devices, ozone doesn't linger long, quickly reacting with living tissue and other compounds.
• Fortunately, since ozone is so unstable, much of it will usually dissipate after sunset.

Ozone Sources

• There are natural sources and man-made precursors for ground level sources.
• Some sources of ground level ozone, such as vehicles and industrial smokestacks, are obvious.
• Other sources are not so obvious, such as gas stations, outboard motors, oil-based paints, and household products, as well as lawn, garden, farm, and construction equipment.
• A certain amount of the precursors to ground level ozone occurs naturally when sunlight interacts with hydrocarbons released from trees. While it's true that trees do produce ozone precursors, research data indicates that in the long run, trees reduce air pollution. Ozone is an unstable chemical. It's a well-established fact that any rough surfaced area will break down airborne ozone. A tree's "rough surfaced area" includes not only its trunk and branches, but its leaf surface area as well.

Northern Shenandoah Valley Air Quality Improvement Task Force
info@valleyairnow.com