16.3 Categories of Air Pollutants Five major types of materials are released directly into the atmosphere in unmodified forms in sufficient quantities to pose a health risk. These are called primary air pollutants. They are: Carbon monoxide Volatile organic compounds (hydrocarbons) Particulate matter Sulfur dioxide Oxides of nitrogen

16.3 Categories of Air Pollutants Secondary air pollutants form under reaction of primary pollutants and water or sunlight. Ozone Criteria air pollutants are those pollutants for which specific air quality standards have been set. Nitrogen dioxide (NO2) Ozone (O3) Sulfur dioxide (SO2) Particulate matter (PM) Carbon monoxide (CO) Lead (Pb)

16.3 Categories of Air Pollutants Carbon monoxide is produced when organic materials are burned with insufficient oxygen. The single largest source is the automobile. 60% from vehicles driven on roads 20% from vehicles not used on roads Remainder from burning, i.e., power plants, leaves, etc. Carbon monoxide binds to hemoglobin in blood and makes the hemoglobin less able to carry oxygen. It is most dangerous in enclosed spaces

16.3 Categories of Air Pollutants Carbon monoxide

16.3 Categories of Air Pollutants Cigarette smoking is an important source because the person is inhaling CO directly. U.S. levels of CO have decreased by about 67% between 1970 and 2007.

16.3 Categories of Air Pollutants Particulate matter consists of minute pieces of solid materials (< 10 microns) and liquid droplets dispersed into the atmosphere. The EPA has set standards for particles smaller than 10 microns (PM10) and 2.5 microns (PM 2.5). Larger than 2.5 microns are primary pollutants; smaller than 2.5 are mostly secondary pollutants. Particulates can accumulate in lungs and interfere with the ability of lungs to exchange gases.

16.3 Categories of Air Pollutants Amount of PM10 has decreased 28% between 1990 and 2007. U.S. EPA has been setting PM2.5 standards for a shorter period of time. Amount decreased 11% between 2000 and 2007. Most communities now meet the standards set for PM10 but exceed the standards set for PM25.

16.3 Categories of Air Pollutants Sulfur dioxide (SO2) is a compound of sulfur and oxygen produced when sulfur-containing fossil fuels are burned. Burning coal releases SO2. Today over 70% of SO2 released into the atmosphere is from coal-burning power plants. U.S. levels of SO2 decreased 56% between 1990 and 2007. Nearly all communities meet the SO2 standards set by the U.S. EPA.

16.3 Categories of Air Pollutants Oxides of nitrogen (NOx) are formed when fossil fuels are burned. The nitrogen and oxygen molecules in the air combine with one another when subjected to the high temperatures of combustion. Nitrogen monoxide (NO) and nitrogen dioxide (NO2) are the most common. Burning fossil fuels in internal combustion engines is the primary source of nitrogen oxides. Automobiles produce 38% Non-road motorized equipment produces 21% Electrical generations produces 22%

16.3 Categories of Air Pollutants About 75% of the NO produced by an automobile engine is converted back into N2 and O2 by the catalytic converter. An increase in the number of cars and miles driven offsets the gains attributable to catalytic converters. Although all communities meet the EPA standards for nitrogen oxides, they remain a problem because they contribute to the development of photochemical smog.

16.3 Categories of Air Pollutants Lead (Pb) can enter the body through breathing airborne particles or consuming lead deposited on surfaces. Lead accumulates in the body and can cause cognitive delay and kidney damage. Leaded gasoline was primary source. Almost all countries have phased out lead as an additive to gasoline. Nearly all gasoline is now unleaded. In the U.S. lead emissions peaked at about 258,000 tons per year. In 2007 they were about 1300 tons per year, a reduction of 99.5%, meeting EPA standards in the U.S.

16.3 Categories of Air Pollutants Volatile organic compounds readily evaporate and become pollutants in the air. They are also known as hydrocarbons The use of internal combustion engines accounts for 37% of VOCs released into the air. Solvents contribute about 22% Fires contribute about 15%

16.3 Categories of Air Pollutants Ozone (O3) is a molecule of three oxygen atoms bonded to one another. It is an extremely reactive secondary pollutant that can: Cause permanent lung damage Irritate respiratory tissues Damage plants Reduce agricultural yields Zone levels fell by only about 9% from 1990 to 2007 and are still a problem particularly in southern California and the U.S. Northeast.

16.3 Categories of Air Pollutants Photochemical smog is a mixture of pollutants. It forms when nitrogen dioxide and VOCs interact in primary pollutants interact under the influence of sunlight. Two most destructive components: Ozone Peroxyacetyl nitrates

16.3 Categories of Air Pollutants Daily changes in photochemical smog

16.3 Categories of Air Pollutants Cities with warm climates and lots of sunlight are more prone to develop photochemical smog. Warm temperatures and sunlight are needed. Smog is more likely to be a problem in the summer with higher temperatures and longer days. Cities adjacent to mountains or in valleys tend to have trouble with photochemical smog because pollutants are trapped by thermal inversions.

16.3 Categories of Air Pollutants Thermal inversions occur when warm air becomes sandwiched between two layers of cold air and acts like a lid on a valley. Warm air cannot rise, causing smog accumulation. Ozone levels fell by about 9% from 1990 to 2007 and are still a problem, particularly in southern California and the U.S. Northeast. Since ozone is produced by VOCs and Nox it is necessary to further reduce the levels of these two components to decrease the production of ozone.

16.3 Categories of Air Pollutants Thermal inversion

16.3 Categories of Air Pollutants Hazardous air pollutants (HAP), or air toxics, are compounds that can harm human health or damage the environment. Some released from consumer activities: Benzene escapes during automobile refueling. Some consumer products such as glues and cleaners release toxic materials into the air. The majority are released from manufacturing: Perchloroethylene is released from dry cleaning processes.