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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 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.

Natural Resource Effects of Ozone

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 ozone exposure levels occur at higher elevations so high elevation vegetation is more at risk. For more information on ozone effects and monitoring, visit http://webcam.srs.fs.fed.us/pollutants/ozone/index.shtml.

Human Health Effects of Ozone

High concentrations of ozone can cause inflammation and irritation of the respiratory tract, particularly during physical activity and can aggravate asthma attacks. The resulting symptoms may include pain when taking a deep breath, coughing, throat irritation, and breathing difficulties. Exposure to ozone can damage lung tissue and increase the susceptibility of the lungs to infections, allergens, and other air pollutants. Medical studies have shown that health problems caused by ozone may continue long after exposure.

In some National Forests, particularly in the Southeast, Northeast and California, ozone concentrations have frequently exceeded standards set by EPA to protect human health. While the Pacific Northwest and Intermountain West typically experience lower levels of ozone pollution than other regions of the country, levels are increasing in the Colorado Plateau and Rocky Mountains regions and sometimes exceed the national standards. For more information on health effects of ozone, visit http://www.epa.gov/airnow/health/smog.pdf.