The U.S. Congress has passed several pieces of legislation to protect the nation's population from the damaging effects of air pollution. The Clean Air Act of 1963 provided federal authority to address air pollution problems on a nationwide basis. The Clean Air Act was amended in 1970, 1977, and 1990. Each amendment modified the Act and provided additional avenues for addressing air pollution problems. As a result of the Clean Air Act and its Amendments, EPA established air quality standards to protect public health and welfare, gained the ability to designate unhealthy areas that needed to be addressed, and dealt with issues such as acid rain and ozone depletion. All 50 states use the Clean Air Act as the basis for the individual state regulations, some more stringent than others. Individual states have the primary responsibility to ensure compliance to both state and federal regulations.

The Clean Air Act Amendments of 1970 required the EPA to set national air quality standards. Standards were set for six major pollutants (also referred to as "criteria" pollutants). For each of these pollutants, EPA tracks two kinds of air pollution trends: air concentrations based on actual measurements of pollutant concentrations in the ambient (outside) air at selected monitoring sites throughout the country, and emissions estimates of the tons of pollutants released into the air each year. Despite the progress made in the last 30 years, millions of people live in counties with monitor data showing unhealthy air for one or more of the six major pollutants.

The major pollutants that EPA currently has standards for are: particulate matter (PM), sulfur dioxide (SO₂), volatile organic compounds (VOC), carbon monoxide (CO), nitrogen oxides (NOx), ground level ozone (O₃) and lead (Pb). Lead levels have been significantly reduced since leaded gasoline has been phased out, but it still poses a serious health risk. There are also very few places in the country that have carbon monoxide, sulfur dioxide or nitrogen oxide levels above EPA standards, therefore the majority of effort goes into monitoring ground level ozone and particulate matter which remain as significant air quality issues in the United States. The air pollutants are measured in several areas of the country by monitoring stations and the data for some pollutants is offered in real time via the web. EPA's AIRNow web site (http://www.epa.gov/airnow/) is dedicated to coordinating and displaying available real time data. The web site contains U.S. maps of current particulate matter and ground level ozone data. Users can also access local information through the site and view all the locations of the monitoring stations and the data being received from the monitoring stations. More detailed lessons using the AIRNow web site can be found in the ground level ozone and particulate matter areas of the Air Pollution: What's the Solution project?

Pollutants are released into the air through a variety of pathways.

Some pollutants are emitted directly into the air. An example is sulfur dioxide (SO₂) which is a colorless corrosive gas produced by fuel combustion. It can directly harm plants and animals and is a precursor of acid deposition (acid rain) since SO₂ combines with water to form sulfuric acid.

Some air pollutants are created from a combination of two or more pollutants after they have been directly emitted into the environment. Ozone (O₃) is an example of such a pollutant because it is formed by a series of chemical reactions in the atmosphere involving nitrogen dioxide, volatile organic compounds and sunlight.

Is it a Solid, Liquid, or a Gas?
Depending on the ability level of your students, it might be valuable to review the following information about States of Matter.

Please do not be concerned if you or your students do not possess a strong chemistry background. This lesson may seem a little chemistry heavy, but the terms are explained or defined in a readable format within the lesson and also can be found in the project glossary. The Project Leader (lhotalin@stevens.edu) is always an e-mail away if there are any questions about the lesson.

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