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Air Quality 101

Air Pollutants

Emission Sources

Regulatory Programs

Air Pollutants

A number of air pollutants can cause damage to health. Six major air pollutants (carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter and sulfur dioxide) have been identified as causing health effects at concentrations in the ambient air (the outside air we breathe) above thresholds established at levels known to be safe.

These pollutants are referred to as criteria pollutants, and National Ambient Air Quality Standard (NAAQS) has been established for each based on health-related criteria and data.

Criteria Pollutants

Carbon Monoxide (CO)

Carbon monoxide is produced primarily by motor vehicles. It can reduce a person's ability to think clearly and causes visual impairment and headaches if high enough concentrations are experienced for a long period of time. 
Long-term monitoring in Florida shows a significant decrease in carbon monoxide concentrations. Urban areas that formerly suffered occasional high levels of carbon monoxide are no longer violating the air quality standard. 

As the result of vehicle emissions controls and local measures to reduce traffic congestion, Florida has not recorded a violation of the carbon monoxide standard since 1986.

Lead (Pb)

For many years, lead was primarily emitted to the atmosphere from motor vehicles that burned leaded gasoline. Lead can affect the central nervous system and lead to anemia. The young and the elderly are most susceptible to the harmful effects of lead.

Over the last 10 years, the lead content of fuels has been reduced, and today, almost all fuels are lead-free. With the phase-out of leaded gasoline, exposure to this pollutant by inhalation has become far less likely.

Ambient air concentrations of lead in Florida reflect the decrease in auto emissions. Except for locations very near a small number of stationary sources that emit significant amounts of lead - such as secondary lead smelters - lead concentrations in Florida's air are nearly zero.

Nitrogen Dioxide (NO2)

Nitrogen dioxide, which is a primary component of nitrogen oxides (NOx), is produced when fuel is burned in motor vehicles, power plants, industrial boilers and other sources.

Nitrogen dioxide can place a strain on the heart and respiratory system and can increase a person's susceptibility to respiratory infections.

Monitors in Florida have never measured a violation of the ambient standard for NO2.

The 1990 federal Clean Air Act amendments require further reductions of NOx emissions because of their relationship to acid rain and ozone formation. As a result, we expect no violations of the ambient air quality standard for nitrogen dioxide in the future either.

Ozone (O3)

Ozone is a gas composed of three oxygen atoms. It is formed in a chemical reaction between the diatomic oxygen molecule (O2) and an oxygen atom (O). 

Since there is abundant O2 in the atmosphere, the key to ozone formation is the availability of free oxygen atoms. At ground level, these oxygen atoms are primarily created from the breakup of nitrogen dioxide (NO2) by solar radiation. The amount of NO2 available is regulated by a complex chemistry involving volatile organic compounds (VOCs) and other oxides of nitrogen (NOx) in the presence of heat and sunlight. 

In the upper atmosphere (stratosphere), oxygen atoms are created as a result of the breakdown of the oxygen molecule (O2) by ultraviolet radiation.  

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. Breathing this ozone can result in damage or irritation to the lungs (bad effect).

Stratospheric Ozone Depletion 

Under natural conditions, ozone in the stratosphere is continuously produced and destroyed but at equal rates such that a stable ozone layer is maintained. However, certain human-made chemicals, referred to as ozone-depleting substances, can upset this natural balance. These ozone-depleting substances degrade slowly and can remain intact for many years as they move through the lower atmosphere until reaching the stratosphere. There, they are broken down by the intensity of the sun's ultraviolet rays and release chlorine and bromine molecules, which destroy the ozone. One chlorine or bromine molecule can destroy 100,000 ozone molecules, causing ozone to disappear much faster than nature can replace it. Presently, satellite observations indicate a worldwide thinning of the protective ozone layer. The most noticeable losses occur over the North and South Poles because ozone depletion accelerates in extremely cold conditions. 

The most common ozone-depleting substances are chlorofluorocarbons (CFCs), once widely used as refrigerants and foam blowing agents; halons, used in fire extinguishers; and certain solvents such as carbon tetrachloride. Under the Montreal Protocol, an international agreement ratified by most nations in 1987, the production of CFCs, halons and other ozone-depleting substances has been mostly phased out. However, it can take years for ozone-depleting chemicals to reach the stratosphere. Therefore, some of the ozone-depleting substances that were released in years past are still present in the atmosphere and will affect the ozone layer for many years to come. 

As a result of the thinning of the stratospheric ozone layer, higher levels of ultraviolet-b (UV-b) radiation from the sun is able to reach the Earth's surface. Increased UV-b can lead to more cases of skin cancer, cataracts and impaired immune systems. Damage to UV-b sensitive crops such as soybeans can reduce yield. Ocean phytoplankton could decrease, leading to a decline in populations of higher organisms in the marine food chain. Increased UV-b radiation also can be instrumental in forming more ground-level ozone. 

Ground-level Ozone (Smog) 

Ozone also occurs naturally near the Earth's surface. However, human-made emissions of VOCs and NOx can cause additional ozone, the primary component of urban smog, to be formed. This additional ozone, which can more than triple the amount of natural ground-level ozone, can cause health and environmental damage. Ozone builds up near the ground through a series of complex chemical reactions involving VOCs and NOx in the presence of sunlight. VOCs are produced by natural sources such as trees; 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. NOx is emitted from motor vehicles; off-road engines such as aircraft, locomotives and construction equipment; fossil-fuel-burning power plants and other industrial facilities; and other sources of combustion. 

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 also can increase the susceptibility of the lungs to infections, allergens and other air pollutants. 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. 

The U.S. Environmental Protection Agency has established a health-based air quality standard for ozone. 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.

Particle Pollution

Particle pollution is the general term used for a mixture of solid particles and liquid droplets found in the air. This pollution, also known as particulate matter, is made up of a number of components, including acids (such as sulfates and nitrates), organic chemicals, metals, soil or dust particles, and allergens (such as fragments of pollen or mold spores). 

The size of the particles is directly linked to their potential for causing health problems. Small particles pose the greatest threat. PM2.5 describes the small particles of concern; they are "fine particles" (such as those found in smoke and haze), which are 2.5 micrometers in diameter or less. "Coarse" particles describe particles greater than 2.5 but less than or equal to 10 micrometers in diameter. PM10 refers to all particles less than or equal to 10 micrometers in diameter. Ten micrometers are about one-seventh the diameter of human hair.

Particle pollution originates from many different stationary and mobile sources as well as from natural sources. Fine particles can result directly from emissions of fuel combustion from motor vehicles, power generation and industrial facilities, as well as from residential fireplaces and wood stoves. In other cases, gases such as sulfur dioxide, nitrogen oxides and volatile organic compounds interact with other compounds in the air to form fine particles. Coarse particles are generally emitted from sources such as vehicles traveling on unpaved roads, materials handling, crushing and grinding operations, and windblown dust. Their chemical and physical compositions vary depending on location, time of year and weather. 

When breathed, both fine and coarse particles can accumulate in the respiratory system and are associated with numerous health effects. Exposure to coarse particles is primarily associated with the aggravation of respiratory conditions such as asthma. Sensitive groups that appear to be at the greatest risk of such effects include those with heart or lung disease, older adults and children. In addition to health problems, particle pollution is the major cause of reduced visibility in many parts of the United States. Airborne particles also can impact vegetation and ecosystems and can cause damage to paints and building materials. 

The U.S. Environmental Protection Agency has established two health-based air quality standards for particle pollution, one for PM2.5 and the other for PM10. The Florida Department of Environmental Protection, in cooperation with several county air pollution control agencies, monitors particle pollution air quality throughout the state.

Sulfur Dioxide

Sulfur dioxide (SO2) is produced by power plants and industries that burn fossil fuels containing sulfur, such as coal and oil, and by the phosphate industry through its production of sulfuric acid. SO2 is irritating to the lungs and can result in a higher incidence of respiratory disease.

Florida has made great strides in controlling SO2 since the early 1970s when control strategies were first implemented, but occasional violations of the ambient air standard do occur.

These are usually associated with accidental releases at industrial facilities. Through its enforcement powers, the Florida Department of Environmental Protection requires that the industry determine the cause of any upset and take steps to prevent its recurrence. 

With the passage of the Federal Clean Air Act Amendments of 1990, SO2 emissions from power plants have been reduced significantly. As of the year 2000, power plants across the nation have reduced their sulfur dioxide emissions by about one-half. This should help ensure that Florida does not suffer the harmful effects of acid rain that have occurred elsewhere.

Other Air Pollutants

Acid Rain

Acidic deposition, or acid rain as it is commonly known, occurs when sulfur dioxide (SO2) and oxides of nitrogen (Nox) emissions react in the atmosphere with water, oxygen and oxidants to form acidic compounds. These compounds are then deposited on the Earth's surface in either dry form (gases or particles) or wet form (rain, snow or fog). Prevailing winds transport the compounds, sometimes hundreds of miles, across state and national borders before they are deposited on the surface.

Acid rain can cause acidification of lakes and streams, with the potential to harm aquatic life, and it can contribute to damage to trees.

In addition, acid rain can accelerate the decay of paints and building materials, including buildings, statues and sculptures that are part of our cultural heritage. 

Acid rain occurs in Florida, but the degree of acidity of the state's rainfall is much less than that of the Northeast United States, where most of the ecological damage associated with acid rain has been found. However, Florida does have a number of lakes that are potentially sensitive to acidification by rainfall. 

The federal Clean Air Act limits the emissions of acid-forming pollutants from electric power plants by requiring that sulfur dioxide emissions (in tons) for a given plant in a given calendar year be less than or equal the number of allowances granted them by the EPA Clean Air Markets Division for that year. Shortages must be covered by using banked allowances, or significant fines will be imposed on the plant. Allowances can be banked by saving prior year's allocations and/or purchase on the open market through the Chicago Board of Trade.

DEP's Division of Air Resource Management Office of Air Monitoring performs quality assurance activities on monitoring systems required by the federal Acid Rain Program.

Air Toxics

Air toxics (also called hazardous air pollutants) are those air pollutants known or suspected to cause cancer or other serious health effects, such as reproductive and birth defects. The degree to which a toxic air pollutant affects a person's health depends on many factors including the quantity and toxicity of the pollutant to which the person is exposed as well as the duration and frequency of exposure.

Air toxics can come from natural sources (e.g., radon gas coming up from the ground) or human-made sources such as motor vehicles and industrial processes. Air toxics that deposit onto soil or into lakes and streams can affect ecological systems and eventually human health through the consumption of contaminated food.

The federal Clean Air Act targets 188 toxic air pollutants for emissions reduction. Examples include benzene, which is found in gasoline; perchloroethylene, which is emitted from some dry cleaning facilities; and methylene chloride, which is used as a solvent and paint stripper by a number of industries. Other examples are dioxin, asbestos, and metals such as mercury, chromium and lead. The Florida Department of Environmental Protection ensures that industries in the state comply with the limits on toxic air pollutant emissions established under the Clean Air Act.

Chlorofluorocarbons (CFCs)

The stratospheric ozone layer that exists about 30 miles above the Earth shields its surface from dangerous solar ultraviolet radiation. 

Human-made chemicals such as CFCs break down ozone, rendering it useless for screening deadly ultraviolet radiation and increasing the level of ultraviolet radiation striking the surface of the earth.

This can result in a variety of adverse health effects for people, such as skin cancer, cataracts and weakened immune systems, as well as other problems such as reduced agricultural crop yields.


Mercury is a naturally occurring element present throughout the environment. It becomes a toxic air pollutant when released into the air, water and soil by human activity.

Reactive, inorganic mercury is emitted to the atmosphere primarily from coal-burning power plants and incinerators that combust mercury-containing wastes.

Air currents and rainfall convey this mercury from the atmosphere to the Earth's surface. Some of the deposited mercury ends up in wetlands, lakes and streams where bacteria convert a portion of it into methylmercury, a toxic form that builds up (bioaccumulates) in the tissues of animals at each link in the food chain. 

Human beings are believed to have some tolerance for mercury. Based on this, the Florida Department of Health has established guidelines. Fish that have more than 1.5 parts per million of mercury in the edible flesh are considered unsafe for any consumption. Those containing less than 0.5 parts per million are considered safe for unlimited consumption. Consumption should be limited for fish with concentrations from 0.5 to 1.5 parts per million of mercury in edible flesh.

Women of childbearing age and children should limit consumption of these fish to a single serving per month. Other adults should limit consumption of these fish to a single serving per week. These values are based on a bodyweight of 156 pounds and an 8-ounce (half-pound) serving of fish. If a person weighs less, it would be safer to consume less. A conservative approach for eating largemouth bass from untested waters would be to follow the advice given for limited consumption — one serving per month for women of childbearing age and children, and one serving per week for other adults.

Emission Sources

Stationary and area sources all emit air pollutants into the atmosphere. Stationary sources include utility, industrial, institutional and commercial facilities. Examples are electric power plants, phosphate processing plants, pulp and paper mills, and municipal waste combustors. Area sources include many individual, small activities such as gasoline service stations, small paint shops, consumer solvent use, and open burning associated with agriculture and forest management actives. 

Regulatory Programs

Federal and state regulations keep the air clean by limiting the amount of air pollutants that are emitted from stationary and area sources. The Florida Department of Environmental Protection issues permits for the construction and operation of these sources. DEP confirms that sources are in compliance with applicable regulations through conducting air inspections, reviewing reports and pursuing enforcement. DEP also maintains an annual emissions inventory to track the amounts of air pollutants emitted over time (by individual source and statewide).

Beyond stationary and area sources, DEP implements the federal asbestos program in Florida. The state's regulations ensure that products containing asbestos are handled safely during construction projects; the rules apply to most demolition and renovation projects in the state.

Last Modified:
June 23, 2023 - 2:16pm

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