National Park Service

Northeast Temperate Network (NETN)

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Ozone is a molecule of three oxygen atoms bound together (O3). It is unstable and highly reactive. Ozone is used as a bleach, a deodorizing agent, and a sterilization agent for air and drinking water. At low concentrations, it is toxic.

Ozone is found naturally in small concentrations in the stratosphere, a layer of Earth's upper atmosphere. In this upper atmosphere, ozone is made when ultraviolet light from the sun splits an oxygen molecule (O2), forming two single oxygen atoms. If a freed atom collides with an oxogen molecule, it becomes ozone. Stratospheric ozone has been called "good" ozone because it protects the Earth's surface from dangerous ultraviolet light.

Ozone can also be found in the troposphere, the lowest layer of the atmosphere. Tropospheric ozone (often termed "bad" ozone) is man-made, a result of air pollution from internal combustion engines and power plants. Automobile exhaust and industrial emissions release a family of nitrogen oxide gases (NOx) and volatile organic compounds (VOC), by-products of burning gasoline and coal. NOx and VOC combine chemically with oxygen to form ozone during sunny, high-temperature conditions of late spring, summer and early fall. High levels of ozone are usually formed in the heat of the afternoon and early evening, dissipating during the cooler nights.

Although ozone pollution is formed mainly in urban and suburban areas, it ends up in rural areas as well, carried by prevailing winds or resulting from cars and trucks that travel into rural areas. Significant levels of ozone pollution can be detected in rural areas as far as 250 miles (402 kilometers) downwind from urban industrial zones

Importance & Issues

jefferson salamander Ozone pollution is an important stressor of terrestrial vegetation with clear ecological relevance.  Atmospheric ozone concentration data is available from the CASTNET network and other sources, and need only be acquired and summarized by the NETN.  Ozone stress on specific indicator species should be monitored within some NETN parks to provide the necessary information to better ascertain the ecological effects of ozone.  Ozone monitoring is presently ongoing at Acadia and Saratoga. Acadia is a Class 1 air quality park and therefore has a GPRA goal to maintain or improve park air quality. Other parks are within 35 miles of an ozone monitoring station, and therefore it is not necessary to install any new ozone monitoring stations. 

Monitoring Objectives:

NPS monitoring objectives are:

- Identify air pollutants which may injure or damage park natural resources, measure these pollutants, and correlate observed effects on resources to ambient levels of pollutants.

- Establish baseline visibility conditions, deposition, and air pollutant concentrations in national parks.

- Identify and assess trends in air quality.

- Determine compliance with National Ambient Air Quality Standards.

- Provide data for the development and revision of national and regional air pollution control policies that are protective of park resources.

- Provide data for atmospheric model development and evaluation.

- Determine the relative importance of various atmospheric constituents to visibility impairment.

- Determine the sensitivity of individual areas or views to variations in visual air quality.


Atmospheric Ozone concentration (synthesize existing data), foliar injury to indicator species.


Last Updated: December 30, 2016 Contact Webmaster