OUTDOOR AIR POLLUTANTS

Ozone is a wide-ranging air pollution problem in much of the country. Ozone is a gas composed of three oxygen atoms. Ozone is “good” high in the atmosphere protecting us from harmful ultraviolet rays. However, ozone is “bad” when created at ground-level. Ground-level ozone is not usually emitted directly into the air, but created by a chemical reaction between oxides of nitrogen (NO_x) and volatile organic compounds (VOC) in the presence of heat and sunlight. As a result, it is known as a summertime air pollutant with the highest levels occurring during hot, dry days with little to no wind. Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents are some of the major sources of NO_x and VOC that help to form ozone. Many urban areas tend to have high levels of "bad" ozone, but even rural areas are also subject to increased ozone levels because wind carries ozone and pollutants that form hundreds of miles away from their original sources. Ozone can irritate lung airways and cause inflammation much like a sunburn. Other symptoms include wheezing, coughing, pain when taking a deep breath and breathing difficulties during exercise or outdoor activities. Ozone can cause permanent lung damage after long-term exposure. People with respiratory problems, such as asthma, and children are most vulnerable. Long-term exposure to ozone can also increase sensitivity to certain allergies, like dust mites.

Nitrogen oxides (NO_x ) is another type of air pollution that can worsen asthma symptoms. Nitrogen dioxide, a main ingredient of ozone formation, is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. Many of the nitrogen oxides are colorless and odorless. However, one common pollutant, nitrogen dioxide along with particles in the air can often be seen as a reddish-brown layer over many urban areas. Nitrogen oxides form when fuel is burned at high temperatures. The primary sources of NO_x are motor vehicles, electric utilities, and other industrial, commercial, open burning of yard waste and trash, and residential sources that burn fuels. Though NO_x is usually found at higher levels outdoors, unvented gas stoves or heaters can produce high levels of NO_x indoors which may worsen asthma symptoms.

Sulfur dioxide (SO₂ ) belongs to the family of sulfur oxide gases (SO_x ).  Sulfur is present in many raw materials, including crude oil, coal, and ore that contains common metals like aluminum, copper, zinc, lead, and iron.  SO_x gases form when fuel containing sulfur, such as coal and oil, is burned, and when gasoline is extracted from oil, or metals are extracted from ore.  SO₂ dissolves in water vapor to form acid, and interacts with other gases and particles in the air to form sulfates and other products that can be harmful to people and their environment. Over 65 percent of SO₂ released to the air, or more than 13 million tons per year, comes from electric utilities, primarily those that burn coal.  Other industries that emit SO₂ are petroleum refineries, cement manufacturing, and metal processing facilities. Also, locomotives, large ships, and some non-road diesel equipment currently burn high sulfur fuel and release SO₂ emissions to the air in large quantities. High levels of SO₂ emitted over a short period of time, such as a day, can cause asthma symptoms to occur or persist in people with asthma.

Fine Particles are elements floating in the air, including dust, dirt, soot, smoke, and liquid droplets.  Particles can be suspended in the air for long periods of time.  Some particles are large or dark enough to be seen as soot or smoke.  Others are too small to be seen with the naked eye and can only be detected with a microscope. Some particles are directly emitted into the air. They come from a variety of sources such as cars, trucks, buses, factories, construction sites, tilled fields, unpaved roads, stone crushing, and burning of wood and trash. Other particles may be formed in the air from the chemical change of gases or condensation much like water vapor forming steam. These can result from fuel combustion in motor vehicles, at power plants, and in other industrial processes. Additionally, pollen spores can attach to fine particles compounding the affect on people with asthma and pollen allergies.

Hazardous Air Pollutants, also known as air toxins, are emitted into the air from thousands of sources and can have serious harmful health effects, including damage to the respiratory system. The U.S. EPA has listed 188 hazardous air pollutants that can be damaging to human health. Examples of toxic air pollutants include benzene, which is found in gasoline; perchlorethlyene, 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 important air toxins listed that may affect respiratory health include: dioxin, asbestos, and toluene.

Volatile Organic Compounds (VOCs) are a family of carbon-based chemicals that evaporate. For e xample, ethylene, propylene, benzene, or styrene, changes into a vapor at a relatively low temperature and contributes to air pollution and ozone formation. F or instance, VOCs + NO_x + Heat + Sunlight = Ozone. VOCs are compounds that evaporate from the many housekeeping, maintenance, and building products made with organic chemicals. These compounds are released from products that are being used and that are in storage. VOCs are also a major part of environmental tobacco smoke.