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	USDA Forest Service 1400 Independence Avenue SW Washington, D.C. 20250-0003 (202) 205-8333

Ozone

Ozone is a colorless gas that exists naturally in the upper atmosphere where it shields the earth from the sun’s harmful ultraviolet rays. Ozone close to the earth’s surface is an air pollutant. It is formed by chemical reactions between volatile organic compounds (VOCs) and oxides of nitrogen in the presence of sunlight and, often, elevated temperatures. The primary human sources of VOCs and nitrogen oxides are industrial and automobile emissions. Ozone can be transported hundreds of miles to remote areas of the country.

Monitoring Ozone Effects on Forest Health

An example of ozone symptoms on a leaf. Photo courtesy of Sharon Grant.

Ozone is one of the most toxic air pollutants to plants. It causes considerable damage to vegetation throughout the world. Plants are generally more sensitive to ozone than humans. The effects of ozone on native plants in natural ecosystems range from visible injury to the leaves and needles of deciduous trees and conifers to premature leaf loss, reduced photosynthesis, and reduced growth in sensitive plant species. Other factors, such as soil moisture, presence of other air pollutants, insects or diseases, genetics, or topographical locations can lessen or magnify the extent of ozone injury. For example, higher elevations typically see higher ozone exposure levels leaving high elevation vegetation more at risk. Learn more about ozone impacts to forests.