Emissions

Carbon Monoxide

Carbon monoxide is an odorless, colorless, and toxic gas. Known sources for carbon monoxide are unvented kerosene and gas space heaters; leaking chimneys and furnaces; back-drafting from furnaces, gas water heaters, wood stoves, and fireplaces; gas stoves; generators and other gasoline-powered equipment; and tobacco smoke. Incomplete oxidation during combustion in gas ranges and unvented gas or kerosene heaters may cause high concentrations of CO in indoor air. Worn or poorly adjusted and maintained combustion devices (such as boilers or furnaces) can be significant sources, as can the flue if it is improperly sized, blocked, disconnected, or leaking. Automobile, truck, or bus exhaust from attached garages, nearby roads, or parking areas can also be a source. The effects of CO exposure can vary greatly from person to person depending on age, overall health, and the concentration and length of exposure.

Lead

Lead's toxicity has been recognized for more than a century; the metal is associated with the impairment of neural development in infants and young children and with cardiovascular disease and premature death in older people. Governments have long tried to reduce exposure by controlling industrial emissions, removing lead from gasoline, and mounting campaigns to remove lead-based paint from homes. In the United States, some of the highest lead levels in blood can be found in children in older cities like Philadelphia, Pennsylvania; Providence, Rhode Island; and Cleveland, Ohio. In 2008, the EPA set new limits for exposure at 0.15 micrograms per cubic meter of air, down from 1.5 micrograms.

Nitrogen Dioxide

Nitrogen dioxide is a highly reactive oxidant and corrosive gas. The primary sources indoors are combustion processes, such as unvented combustion appliances like gas stoves, vented appliances with defective installations, welding, and tobacco smoke. Effective measures to reduce exposures to this gas are venting the NO2 sources to the outdoors and assuring that combustion appliances are correctly installed, used, and maintained.

Ozone

Ozone is a molecule consisting of three oxygen atoms. Ozone in the lower atmosphere is an air pollutant with harmful effects on sensitive plants and the respiratory systems of animals. The ozone layer in the upper atmosphere is beneficial, preventing potentially damaging ultraviolet light from reaching the Earth's surface. Exposure to ozone has been associated with premature death, asthma, bronchitis, heart attack, and other cardiopulmonary problems. The EPA lowered its ozone standard from 80 parts per billion (ppb) to 75 ppb in 2008. Nevertheless, the World Health Organization recommends 51 ppb.

Particulate Matter

Particulate matter is a mixture of very small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles. According to the EPA, the size of particles is directly linked to their potential for causing health problems. Particles that are 10 micrometers in diameter or smaller can pass through the throat and nose, invading the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. The EPA groups particle pollution into inhalable coarse particles (those found near roadways and dusty industries, larger than 2.5 micrometers and smaller than 10 micrometers in diameter) and fine particles (those found in smoke and haze that are 2.5 micrometers in diameter and smaller). These particles can be directly emitted from sources such as forest fires or they can form when gases emitted from power plants, industries, and automobiles react with other substances in the air.

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