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New Hampshire Department of Environmental Services


What is Ozone (Ground-Level Ozone, or "Smog")?
Ozone is a colorless gas that can be found throughout the earth’s atmosphere. In the upper atmosphere, ozone exists naturally where it shields the earth from the sun’s ultraviolet rays. At ground-level, however, ozone is formed as a result of chemical reactions caused by the presence of nitrogen oxides (NOx) and volatile organic compounds (VOCs). These compounds react with oxygen in the air in the presence of heat and strong sunlight to produce ground-level ozone, the primary ingredient of summertime smog. Ground-level ozone is one of the six criteria air pollutants (see "Related Programs") identified by the US Environmental Protection Agency under the federal Clean Air Act. Because of the health effects and the widespread nature of ground-level ozone, it has been a major focus of air quality regulatory agencies across the country. These efforts have included ambient air quality monitoring and providing air quality forecasts to inform the public when ozone levels are anticipated to be high. More recently, air agencies have undertaken similar efforts to address fine particulate matter.

As the major ingredient in summertime smog, ozone has strong oxidizing properties that irritate, and in some cases, damage lungs, throat, and eyes. Ozone can limit the ability to take a deep breath, and it can cause coughing, throat irritation, and breathing discomfort. Children and those with pre-existing lung problems, such as asthma, are more sensitive to the harmful effects of ozone. Even healthy adults involved in moderate or strenuous outdoor activities can experience the unhealthy effects of ozone exposure. An "Air Quality Action Day" is called in New Hampshire when ozone is forecast to reach unhealthy levels. During an Air Quality Action Day, people are encouraged to take precautionary measures to protect their health, especially in the afternoon when ozone levels tend to be the highest.

Ozone also inhibits foliage growth and can severely reduce plants’ ability to reproduce, often leaving plant life weakened and susceptible to insect infestation and cold weather damage.

As mentioned earlier, VOCs and NOx contribute to the formation of ground-level ozone and smog. Sources of VOC and NOx emissions are many and varied. Almost all NOx emissions originate from human activities and are formed from fossil fuel combustion, principally from power plants, industrial boilers, and cars and trucks. Conversely, over 85 percent of VOC emissions in New Hampshire result primarily from forests and other vegetation. Other VOC sources include cars and trucks, solvents and paints, storage and distribution of gasoline, and manufacturing facilities.

On a tonnage basis, the amount of smog-causing air pollutants emitted in New Hampshire is very small when compared to the amount emitted by major cities and power plants upwind of the state (to the south and southwest). In fact, most of the ozone problems experienced in New Hampshire occur along the southern and southeastern border of the state, or at higher elevations, when the wind enters the region from the south, southwest, and southeast, or from out-of-state.

National Ambient Air Quality Standards for Ozone
To protect human health and welfare from damaging levels of air pollution, the Clean Air Act of 1970 established a process for setting National Ambient Air Quality Standards (NAAQS) for ozone, as well as several other criteria air pollutants. In the case of ozone, a standard for a one-hour average concentration of 120 parts per billion (ppb) was set for protection from intense short-term exposures.

In 1997, the US Environmental Protection Agency promulgated a more protective eight-hour average ozone standard of 80 ppb on the basis that longer-term exposure to elevated levels of ozone can be just as damaging, if not more damaging, than shorter exposures to very high levels of ozone. The one-hour ozone standard was revoked on June 15, 2005 in favor of the more stringent eight-hour ozone standard.

In 2008, EPA revised the eight-hour average standard to 75 ppb, a more stringent standard, based on scientific evidence that the existing eight-hour standard did not adequately protect public health from the harm caused by ozone. This new eight-hour standard was not as stringent as recommended by EPA’s Clean Air Science Advisory Committee, which was to lower the standard to within a range between 70 and 60 ppb. NHDES has joined other states in bringing suit against the EPA for failing to adequately protect public health in setting the new eight-hour standard.

New Hampshire’s Ozone Attainment Status
The Clean Air Act Amendments of 1990 require areas that do not meet the NAAQS for criteria pollutants to submit a State Implementation Plan (SIP), which is a set of technical analyses and documents that outline how the area plans to achieve attainment with the standards.

Because New Hampshire had areas that violated the one-hour standard for ozone, NHDES submitted a State Implementation Plan (including technical analysis) to show how the state would achieve compliance with the one-hour NAAQS for ozone. This analysis was submitted as the One-Hour Ozone Attainment Demonstration in 1998 and included descriptions of the air pollution reduction programs that New Hampshire was, or would be, undertaking to achieve attainment with the ozone standard.

When the 1997 eight-hour ozone NAAQS was promulgated, New Hampshire once again had areas not meeting the standard and was required to submit a SIP detailing how the state would achieve compliance. This process was altered and delayed due to litigation of not only the ozone standard, but the fine particulate matter standard which was also revised in 1997. New Hampshire submitted its proposed attainment demonstration, entitled "New Hampshire 8-Hour Ozone State Implementation Plan," in June 2007. Again, this demonstration outlined the air pollution reduction measures that New Hampshire has adopted or is proposing to commit to, as well as the technical analyses to support the conclusion that the eight-hour ozone standard will be attained.

Ozone Transport
Attaining the ozone standard in New Hampshire requires more than just reducing emissions within the state. Much of the ozone (and its precursors) that is experienced in New Hampshire is transported from other regions upwind of the state. New Hampshire has already made significant progress in reducing its own emissions of ozone-producing compounds. However, the pollutant transport phenomenon makes it even more difficult to attain air pollution standards. To ensure that other regions do their fair share in reducing pollution, NHDES in 1997 filed a petition under Section 126 of the Clean Air Act to show that attaining the ozone standard in this state depends on reductions in ozone precursor emissions in other states. Further, in March 2008, NHDES submitted a SIP revision to certify that emissions activities in New Hampshire do not contribute to nonattainment of the eight-hour ozone NAAQS or the 1997 fine particulate matter NAAQS in other states or interfere with the maintenance of either NAAQS in other states. This SIP revision was detailed in a document entitled "Revision to the New Hampshire State Implementation Plan to Meet the Requirements of Clean Air Act Section 110(a)(2)(D)(i)," or more commonly referred to as the Transport SIP.

NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

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