Ozone (O3) is a gas composed of molecules consisting of three oxygen atoms. This form of molecular oxygen is present in the atmosphere in small concentrations. At ground level O3 is considered a pollutant; at high enough concentrations it has various toxic effects on plants and animals, including people. In contrast the concentration of O3 that exists between 15 and 50 km above the earthÕs surface in the stratosphere is beneficial. It is this layer of O3 that absorbs most of the harmful ultraviolet radiation from the sun.
Tropospheric ozone is measured in parts per billion. In 1979, the U.S. Environmental Protection Agency established a national ambient air quality standard (NAAQS) for ozone. The upper limit for ozone is 120 parts per billion (ppb) for a one-hour average. To determine whether this standard is being met, the number of days when this one-hour average is exceeded are totaled over a three year period. If the average number of days per year during which the ozone limit was exceeded is less than or equal to 1.0, the standard is being met.
Previously, the standard was based on the total amount of photochemical oxidant with an upper limit of 80 ppb. Photochemical oxidants are a family of chemicals; ozone is only one of these. However, it turns out that the instruments used to measure photochemical oxidants primarily measure ozone since it is the most abundant species.
In general, the levels of ozone pollution in the U.S. are getting better.
In the United States the Federal Government operates the Environmental Protection Agency. This institution is responsible for regulating and monitoring pollution in the environment. The EPA operates air monitoring stations around the country where ozone is just one of the pollutants that is monitored. Each state in the United States also has a state version of the EPA which shares environmental authority within that state with the federal EPA. In Massachusetts this agency is called the Department of Environmental Protection or DEP. One of the services the EPA provides is periodic calibration of the air monitoring equipment operated by the state. When the state instruments pass the EPA calibration their data can be contributed to the regional and national databases maintained by the EPA of all air pollution data. These data are used by the EPA and legislative bodies to evaluate environmental health, and develop new regulations and laws.
You can call the state and federal environmental agencies and ask them about ozone monitoring in your area. Ask to speak to an air monitoring specialist. This person will be able to tell you where and how ozone is measured in your area. The data from these stations are available also. If you have designed a new device and it needs testing you may want to run calibration tests next to the ozone monitoring site. The scientists and technicians are usually very helpful and interested in education.
The EPA and various state agencies have a wide variety of interesting publications on ozone and other pollution related topics. These publications are available free or for a small cost.
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