Air Quality Indicators

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Ground Level Ozone

Ground-level ozone or smog can cause lung damage, throat irritation, and congestion, and is particularly threatening to the very young, elderly, and people with respiratory diseases, such as asthma and emphysema. High ground-level ozone levels can also pose adverse effects on the environment, including damage to vegetation, agricultural crops, property, and soil.

Ground-level ozone is formed from the reaction of volatile organic compounds (VOC) and nitrogen oxides (NOx) in the presence of strong sunlight when temperatures are high, primarily between June and September. VOC emissions come from vehicle exhaust, paints and solvents, and industrial facilities. NOx is formed primarily as the result of combustion. Sources include power plants, industrial processes, lawn equipment, and vehicles.

A measurable set of indicators of ambient air quality are the National Ambient Air Quality Standards, established by the U.S. EPA as a requirement of the 1990 Clean Air Act for pollutants considered harmful to public health and the environment. These indicators include lead, sulfur dioxide, nitrogen dioxide, particulate matter, carbon monoxide, and ground-level ozone. Of these six indicators, the Washington D.C. area is in compliance with the initial five. However, each year there are a number of days during which the ground-level ozone level in the area exceeds the national standard (the current regulatory standard for ground-level ozone for the Baltimore-Washington metropolitan area is 0.12 parts-per-million, as a one-hour average concentration not to be exceeded more than once a year), as shown below:

Exposure to radon has been recognized as a health risk, primarily as a cause of lung cancer. A study of miners found that inhaling the decay products of radon increases the chances of lung cancer (Robillard and others, 1991).

The Surgeon General of the United States has recognized radon gas as being second only to cigarette smoking as a cause of lung cancer (U.S. Environmental Protection Agency, 1992). Radon gas can cause lung cancer if inhaled because the products of its decay can accumulate in the lungs and damage lung tissue. As it decays, radon produces several short-lived elements that are also radioactive. Radon and these decay-products emit alpha particles that, because of their high energy, can damage lung tissue (Brooks, 1988). Although most radon is exhaled before it can do much damage (Hurlburt, 1989), the decay-products can remain trapped in the respiratory system, attached to dust, smoke, and other fine particles from the air. Eventually, the concentration of these radioactive elements in constant, close contact with lung tissue can cause cancer (Zapecza and Szabo, 1988).

Radon is a naturally occurring, colorless, odorless gas that is soluble in water. It is radioactive, which means that it breaks down - or "decays" - to form other elements. The rate of radon's radioactive decay is defined by its half-life, which is the time required for one half of any amount of the element to break down. The half-life of radon is 3.8 days (Hem, 1985).

The source of radon is the radioactive decay of uranium. Therefore, higher radon amounts are commonly detected in areas underlain by granites and similar rocks that usually contain more uranium than do other rock types (Faure, 1986). Radon moves from its source in rocks and soils through voids and fractures. It can enter buildings as a gas through foundation cracks or dissolve in the ground water and be carried to water-supply wells.

The amount of radon in air or water commonly is reported in terms of activity with units of picocuries per liter of air or water. An activity of 1 pCi/L (picocuries per liter) is about equal to the decay of two atoms of radon per minute in each liter of air or water (Otton, 1992).

Radon gas commonly enters the air in homes through the basement. Ground water can carry additional radon into homes and other buildings, creating a health risk. Dissolved radon is easily released into the air when the water is used for showering, cleaning, and other everyday purposes. The radon, therefore, commonly is released in close proximity to those using the water (fig. 1). Also, in homes built with better insulation and better seals on windows and doors, radon has less chance to be ventilated to the outside and can become concentrated to dangerous levels in indoor air. Most radon escapes from the water at the faucet, leaving little in the water itself (Hurlburt, 1989). The radon that escapes from the water adds to the radon that enters the home through the basement, and in some cases the water contributes a large portion of the radon that is present in a home.

Water-borne radon is commonly a concern only for those who use wells for their water supply. Because of its short half-life, radon in public water supplies usually decays to low concentrations before the water is delivered to users, especially if the water has been treated. Also, public suppliers often use surface-water supplies, which generally have very low radon concentrations (Zapecza and Szabo, 1988).

For more information about radon, radon risks, testing, and mitigation, visit the DEP Radon Homepage now.

Geologic Radon Potential Map

Click on image to view a full representation of radon
potential in Montgomery County by zip code area.

Source: Miscellaneous Field Investigations Map MF-2043: Map showing radon potential of rocks and soils in Montgomery County, Maryland, L.C.S. Gundersen, G.M. Reimer, C.R. Wiggs, and C.A. Rice; scale 1:48,000, 1988.

Carbon Monoxide

Carbon Monoxide (CO) is an odorless, colorless, and tasteless gas produced by incomplete combustion of fuels (including liquid fuels such as gasoline, kerosene, and propane; solid fuels such as wood, coal, and charcoal; as well as natural gas). CO is usually present in our homes in small quantities and is normally not a problem. Exposure to high levels of CO gas can cause CO poisoning to occur and because CO is not detectable by ordinary senses, it can cause injury or death before anyone knows it is present. The flu-like symptoms of CO poisoning include: headache, fatigue, nausea, dizziness, and irritability. At higher levels, CO can cause vomiting, loss of consciousness and, eventually, brain damage and death.

Indicators: Calls to Montgomery County Fire and Rescue regarding CO detectors triggered and number of people sickened by CO exposure.

Year Reported

1997

1998

Calls about CO detector alarms

1,063

878

Calls about sickness from exposure