Air Quality Monitoring

Ozone Standard

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What is ozone?

Ozone (O3) is the principal component of urban smog. Ozone builds up near the ground through a series of complex chemical reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. VOCs are produced by natural and man-made sources. Man-made sources include fuel combustion in engines and industrial operations; some types of chemical manufacturing operations; evaporation of solvents in consumer and commercial products; and evaporation of volatile fuels such as gasoline. Nitrogen oxides are emitted from motor vehicles; off-road engines such as aircraft, locomotives and construction equipment; fuel burning power plants and other industrial facilities; and other sources of combustion.

Ozone has the same chemical structure and properties whether it occurs miles above the earth or at ground level; however, ozone has both good and bad effects depending on its location in the atmosphere. Ozone occurs naturally in the stratosphere approximately 10 to 30 miles above the earth's surface and forms a layer that protects life on earth from the sun's harmful ultraviolet radiation (good effect). In the lower atmosphere, where natural ozone levels are low, additional ground-level ozone is formed as a result of human emissions of VOCs and NOx.

At the ground, ozone concentrations can reach unhealthy levels when the weather is hot and sunny with relatively light winds. Even at relatively low levels, ozone may cause inflammation and irritation of the respiratory tract, particularly during physical activity. The resulting symptoms can include breathing difficulty, coughing, and throat irritation. Breathing ozone can affect lung function and worsen asthma attacks. Ozone can also increase the susceptibility of the lungs to infections, allergens, and other air pollutants. Medical studies have shown that ozone damages lung tissue, and complete recovery may take several days after exposure has ended. In addition, longer-term exposures to moderate levels of ozone present the possibility of irreversible changes in the lung structure which could lead to premature aging of the lungs and worsen chronic respiratory illnesses. Groups that are sensitive to ozone include children and adults who are active outdoors, and people with respiratory disease such as asthma. Sensitive people who experience effects at lower ozone concentrations are likely to experience more serious effects at higher concentrations.

Ozone season is generally from spring to early fall, however the Florida Department of Environmental Protection, in cooperation with several county air pollution control agencies, monitors ozone air quality in Florida's major urban areas year round (see Figure 1 and 2).

Ozone standard

In 2008, the National Ambient Air Quality Standard (NAAQS) for the pollutant ozone, was lowered from 0.084 parts per million (ppm) to 0.075 ppm. Compliance with this primary (health-protective) standard at 0.075 parts per million (ppm) is based on the three-year average of the annual fourth-highest maximum daily eight-hour ozone concentration. In 2010, the U.S. Environmental Protection Agency (EPA) announced proposed revisions to the ozone NAAQS to a value in the range of 0.060 ppm to 0.070 ppm. This proposal has been withdrawn until the next regularly scheduled review of the ozone standard in 2013, and the standard will remain at 0.075 ppm for the time being.

How often do high ozone levels occur?

High ozone levels only occur on a limited number of days per year, typically from spring through early fall when weather conditions are most conducive to ozone formation. The Air Quality Index forecast alerts sensitive persons to limit prolonged, moderate exertion outdoors on those few days.

Does Florida have areas in violation of the ozone standard?

No areas in Florida violate the 0.075 ppm air quality standard. The map above (Figure 1) shows the most current ozone compliance values for the highest monitor in each county based on 2009-2011.

What has been the trend in ozone levels in Florida?

Ozone levels in Florida, and the entire eastern United States, have come down over the past 20 years or so, and this trend is expected to continue. This improvement in air quality has been the result of ongoing, significant emission reductions from industries and individual motor vehicles. The following chart (Figure 2) displays the trend in ozone compliance values across the state over the last ten years. The maximum, minimum, and average ozone compliance values for all ozone monitors in Florida are provided. Since 2008, the trend has been steadily downward, and it is expected to continue so for at least the next several years.

What has been the trend in NOx emissions in Florida?

As stated above, ground-level ozone is formed through a series of chemical reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NOx). Research has found that in Florida and throughout the Southeast, NOx emissions play a more important role than VOC emissions in the formation of ozone.

Figure 3 shows the long-term trend in mobile and stationary source emissions of NOx. Since 2001, the trend has been steadily downward. Preliminary data for 2010 and 2011 show this trend continuing, largely due to emission reductions from electric power plants. NOx emissions from the power sector in Florida have decreased by 80% over the last decade. And, while more vehicles occupy Florida's roads, newer cars and trucks emit less pollution than older ones with the result that overall emissions from motor vehicles are also declining.