NPS: Nature & Science» Air Resources Division-Air Quality Basics

Ozone Effects on Vegetation

Ash Leaf with Ozone Damage

One of the most widespread air pollutants is ozone, which harms vegetation as well as human health. Ozone is not emitted directly from smokestacks or vehicles. It is formed when other pollutants, primarily nitrogen oxides and volatile organic compounds, react in the atmosphere in the presence of sunlight, usually during the warm summer months. Ozone causes considerable damage to vegetation throughout the world, including agricultural crops and native plants in natural ecosystems. The Environmental Protection Agency (EPA) has established an ozone standard to protect human health; however, EPA has not set a standard to protect vegetation and there is much evidence to suggest that the human health-based standard is not protective of sensitive vegetation.

Ozone injury on wild grape

Ozone enters plants through leaf openings called stomata and oxidizes plant tissue, causing changes in biochemical and physiological processes. Both visible foliar injury (e.g., stipple and chlorosis) and growth effects (e.g., premature leaf loss, reduced photosynthesis, and reduced leaf, root, and total dry weights) can occur in sensitive plant species In a natural ecosystem, many other factors can ameliorate or magnify the extent of ozone injury at various times and places such as soil moisture, presence of other air pollutants, insects or diseases, and other environmental stresses. Ozone effects on natural vegetation have been documented throughout the country, particularly in many areas of the eastern U.S. and in California.

For more information on the effects of ozone:

Ozone Sensitive Plant Species on NPS/FWS Lands (PDF .2mb)
Ozone Bioindicators
Technical Information in Support of the Department of the Interior's Request for a Rule to Restore and Protect Air Quality Related Values: Overview of ozone effects on vegetation (.5mb PDF)
USDA Forest Service Ozone Biomonitoring

Specific Park Websites with Ozone Information:

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Ozone Effects on Vegetation