I have had a wonderful 30 year career in the air pollution control field. My specialty is measuring air pollution. I decided a few here might be interested in some of the regulatory, technological, and political aspects to this unusual career. So this is the first in a series of 2 or 3 posts explaining everything you ever wondered about air pollution.
Air pollution is any contaminant added to air that causes damage to other things. These contaminants include both gasses and particles. Some gasses can later convert to particles. Some particles can "evaporate" and become a gas. Some gasses react together in the atmosphere to form different gasses. Nature can be responsible for air pollution, but the vast majority is caused by human activity. The most significant source of human caused air pollution is the burning of fossil fuel, however it is amazing how many other human activities contribute to air pollution emissions.
In 1967 the Air Quality Control Act was passed that required states to set their own air quality standards. After little progress, in 1970 the Clean Air Act was signed into law by Richard Nixon. This was the first step in the US to control air pollution. The initial law at it's base was simple, set standards for allowable concentrations of each type of air pollution and for states that have air quality that exceeds the standards, require each state to demonstrate how they plan to reduce the concentration of their air pollutants below the standards. The standards were called National Air Quality Standards (NAAQS)and were set by a recommendation from a scientific advisory panel and then finalized by EPA staff and ultimately the EPA Director.
The first standards to be set were the common pollutants that mostly result from the burning of fossil fuels. These pollutants (sometimes called criteria pollutants)include both gasses and particles. The criteria pollutants are where most of the air pollution control effort in the US has been focused. Sulfur dioxide resulting from power plants burning high sulfur coal was originally the biggest problem on the east coast. Photochemical smog or ozone was the bigger problem on the west coast. Photochemical smog is a strongly oxidizing soup of chemicals, mostly ozone, that are formed by the reaction of reactive hydrocarbons and oxides of nitrogen in the presence of sunlight. Almost all oxides of nitrogen and most reactive hydrocarbons are the result of cars and trucks, so no wonder that ozone has been the big focus in California. Particulates are typically high in urban areas where particles from fossil fuel combustion can accumulate as well as near places where open un-vegetated soil can be picked up by the wind.
Setting standards by the federal EPA is both a scientific and political process. The recommendation from the scientific advisory panel is completely science with really no political influence. This panel reviews health studies on air pollution in making their recommendation. Once at the EPA, politics as well as weighing economic costs enter into the formula. Many states set their own more protective criteria pollutant standards. The Clean Air Act requires periodic review of these standards and raising or lowering them if the health data indicates a change is appropriate. The EPA did not perform these reviews on a regular schedule as required by law and in 1991 the American Lung Association successfully sued EPA to force these regular reviews of the standards. This has resulted in a lowering of most critieria pollutant standards in recent years. This link is to a table of the current federal and California critieria pollutant standards.
The Clean Air Act has been amended in 1977 and 1990. Chemicals that are harmful and don't normally result from burning fossil fuels are generally called toxic air contaminants, or toxics for short. The 1990 amendment set up control of these pollutants by requiring "maximum achievable control technology" be used on every major source of these pollutants.
Some air pollution measurements were made prior to 1970, but after the passage of the Clean Air Act we needed to measure the concentration of the criteria pollutants across the nation. In designing this air monitoring effort, scientists at EPA realized that it would be important to standardize the way air pollution was measured, so a measurement in New York would be comparable to the same type of measurement in Los Angeles. As a result, EPA designated particular methods as Reference Methods that is the standard way to measure a particular pollutant.
In the early days of air pollution measurements, many different ideas were explored. I knew someone who worked at the Los Angeles Health Department before there was an air pollution control agency in LA, and he told me that in the early days, ozone was measured by pumping outdoor air through rubber tubing. Because ozone (the pollutant of concern) oxidizes rubber and makes it crack after passing air through the tube for a set period, the tube was cut open and the diameter of the cracks in the rubber were measured under a microscope to determine the ozone concentration. Other early measurements were made by manual methods bubbling air through wet chemicals that would react with a particular pollutant that would cause a color change or some other change to the solution that could be measured. Eventually machines that had a complex set of glassware and wet chemicals were invented that somewhat automated these wet chemical methods of air pollution measurement. Later, electronic instruments were developed that measured these pollutants without wet chemicals, usually by detecting some physical property of the pollutant, such as an infrared absorption band that the pollutant has. Today, these automated analyzers are microprocessor controlled sophisticated instruments.
Measuring these pollutants is not an easy thing, even with today's amazing technologies. The first issue is that in most cases we are measuring extremely small quantities of pollutant. The federal ozone standard is currently 75 parts per billion (listed as 0.07 ppm rounds to 0.075 ppm or 75 ppb). You have to understand a part per billion (ppb)is a very small quantity. A ounce shot glass of vermouth in a railroad tanker car of gin, makes a 1 ppm or 1000 ppb martini. One part per billion is like being able to distinguish one individual in all of the people of China. So a ppb is very, very small. The other challenge is that there is a lot of other stuff in the air that can get in the way or bias the measurement of the pollutant. For example, water and CO2 that are quite abundant in the air have some similar infrared absorption bands as carbon monoxide, a criteria pollutant.
EPA gathers measurement data from across the country in a national data base called the Air Quality System (AQS). This data is analyzed to determine what areas of the country have air quality that meets the standards or not. Here is a Link to a map of the US designating the areas of non-attainment for the federal ozone standard. Note the areas of high population and sunshine dominate the non-attainment areas. Here is a link to a map of the US designating non-attainment areas for PM2.5 (fine diameter particulate).
Once an area is designated non-attainment, that state has responsibility under the Clean Air Act to develop a plan to reduce emissions to the point that the air quality data would not exceed the NAAQS. Computer models are used to forecast how much reduction in emissions are needed to result in air that does not exceed the NAAQS. These plans (calles SIP's or State Implementation Plans) are submitted
to EPA for approval. If your area exceeds the NAAQS for any criteria pollutant, your state has submitted a SIP to EPA detaining what control measures and the timeline for implementation that are going to be used to meet the NAAQS. For areas that already meet the NAAQS, if a major new source of pollutant is proposed, the Clean Air Act requires the implementation of Prevention of Significant Deterioration or PSD procedures. PSD requires that computer models calculate the expected impact to existing air quality by the new source and that this impact be below specific demiminus levels, definitely below the NAAQS. If there is not representative data already gathered to make these calculations, the source is required to gather that data, usually for one year prior to construction of the project so that the computer models can be run to determine the impact from the proposed source. The idea of the PSD rule is to prevent any area that meets the NAAQS from slipping backward on their air quality.
These procedures of the Clean Air Act have worked quite well for criteria pollutants. All areas of the country have seen dramatic reductions in the levels of these criteria pollutants. In California ozone levels in most urban areas have dropped to half or less from what they were in the 1960's and 1970's. Sulfur dioxide levels in the eastern part of the US have also dropped dramatically to the point that now most areas now meet the SO2 NAAQS. These improvements have not happened by accident. They have occurred by regulations that have required industrial sources and cars to be much cleaner. We have all paid for these improvements by higher priced cars and products. But in the end we have saved much larger amounts of money by reducing health care and other costs. For example, ozone concentrations in the 1970 were responsible for over 50% reductions in citrus yields in southern California. Health costs and lost work time are also huge economic costs of air pollution that we have reduced dramatically by these regulations. Air Pollution regulations are a clear success story that is not communicated to the public and should be.
So this posting outlines some of the history of air pollution control. My next posting will go into more detail of what each criteira pollutant is, what the sources are and what methods are used to measure it. I hope some of you learned something from this posting. Please hit me with any follow up questions in the comments or feel free to email (my address is in my profile).