April 2013: Air Toxics

This is the fourth article in a series about air quality in general and how it applies to Indiana. I am planning to publish an article every two weeks to cover air pollution topics. My third article covered monitoring of criteria pollutants. This article will discuss air toxics.

Air toxics are compounds that the U.S. Environmental Protection Agency (U.S. EPA) believes or suspects can cause adverse health effects. However, they have not established ambient air quality standards for these compounds. The original list of affected compounds can be found on the U.S. EPA website. This list has been revised slightly over time. You will notice that in some cases a specific compound is not listed, but a category, such as polycyclic organic matter or radionuclides. Further U.S. EPA guidance defines exactly what compounds are included in these categories.

The health effects from these compounds vary. Some cause cancer, others are thought to cause cancer, while others have noncancerous impacts. The health effects notebook, found on U.S. EPA’s website, lists the effects of many of these pollutants.

One of the problems with air toxics is that they are not all created equal. As mentioned above, some cause cancer and some do not. Some have rather nasty health effects, others do not. The levels at which impacts occur can vary significantly. Thus comparing total emissions of air toxics between states, as is often done with the Toxic Release Inventory (TRI) information, does not really show how much improvement has been made. Large reductions in total pounds of compounds that have little impact may look good on paper, but really do not significantly improve the air quality.

Indiana has measured the levels of many air toxic compounds since 1999 at areas of the state where it is expected to find the highest concentrations of air toxics. A report describing the data for the period 1999 - 2008 [PDF] can be found on IDEM’s website. Approximately 10 sites are operated each year and sample about 60 compounds.

Most air toxics are of concern in a fairly small geographical area, relatively close to the source of the air toxic and are addressed on a case by case basis, unlike criteria pollutants that are evaluated on a regional scale. Benzene however is the highest cancer causing compound that we monitor of greatest concern because the impacts are widespread. Benzene is observed at elevated concentrations not only at all Indiana sites, but all national sites. Benzene is a constituent of gasoline and is therefore located where mobile sources are located. Since motor fuel is regulated by U.S. EPA, it is extremely difficult for states to make local revisions to lower the risk. Such a change would need to be made at the national level. The highest noncancer compound found is acrolein. This chemical is related to combustion products. Therefore it is in power plant emissions (coal, oil or gas), in stacks from industries or homes that heat with coal, oil or gas, and is also in cigarette smoke. Once again the levels seen nationally are at levels of concern at every site where acrolein is measured. The toxicity of this compound is currently being reevaluated and the health impacts from it may be revised based on newer information.

At those sites where we have several years of data, there are few trends in the levels of air toxics. They are neither increasing or decreasing at levels that are significant. In most cases this is expected. Unless there is a national program to target a specific chemical, there is little reason that the level of that compound would change.

Happy Earth Day.