Air Toxics: Toxic Air Pollutants

Title III of the amendments deal with air toxics. Toxic air pollutants (TAPs) or air toxics, and also known as hazardous air pollutants (HAPs) are airborne pollutants that are known to have adverse human health effects, such as cancer. Currently, there are about 189 chemicals identified on the CAA list of HAPs or TAPs (Table C.2) (USEPA 1998). Examples of air toxics include the heavy metals mercury and chromium, and organic chemicals such as benzene, hexane, perchloroethylene (perc), 1,3‐butadiene, dioxins, and polycyclic aromatic hydrocarbons. The HAPs are regulated under the national emissions standards for hazardous air pollutants (NESHAP) program were identified as causal agents for a variety of diseases. For example, arsenic, asbestos, benzene, coke oven emissions, and radionuclides may cause cancer. The Title III amendment requires the EPA to list source categories that emit one or more of the air toxics and to publish a schedule for regulation of those categories.

Table 4.7 U.S. emissions of conventional pollutants, 2006 and 2016 (million tons per year).

Source: Compile from data from USEPA, Clearinghouse for Inventories and Emissions Factors, U.S. EPA http://www.epa.gov/ttn/chief/trends/index.html.

Misc. CO is almost all from fires; Misc. PM‐10 is almost all fugitive dust from paved and unpaved roads, construction sites, and agriculture sources.

^a Non‐road includes boats, planes, trains, construction equipment, lawn, and garden equipment, and others.

The CAA defined a major source of HAPs as a stationary source that has the potential to emit 10 T/Y of any one HAP on the list or 25 T/Y of any combination of HAPs. Examples include chemical complexes and oil refineries. The CAA prescribes a very high level of pollution control technology for HAPs called MACT (maximum achievable control technology). Small area sources, such as dry cleaners, emit lower HAP tonnages, but taken together they are a significant source of HAPs. Emission reductions can be achieved by changes in work practices such as material substitution and other pollution prevention strategies.

HAPs affect human health via the typical inhalation or ingestion routes. HAPs can accumulate in the tissue of fish, and the concentration of the contaminant increases up the food chain to humans. Many of these persistent and bioaccumulative chemicals are known or suspected carcinogens. Mercury has been especially targeted for regulation because it is released during the combustion of coal. Thus, it is one of the few HAPs that is widespread in the environment. Of particular concern are children who are exposed to methylmercury prenatally (USEPA 1997, 2004a).

Title IV addresses acid deposition, calling for a nationwide SO₂ emissions reduction of 10 million T/Y from 1980 levels, primarily from electric utilities. It promotes energy conservation and clean coal technologies and utilizes an innovative market‐based system for the SO₂ reductions, in which utility allowances for SO₂ emissions can be bought and sold. In addition, USEPA is required to develop a revised NO _x new source performance standards (NSPS) for utility boilers.

Title V establishes a new federal operating permit program to be administered by the states. States had three years to implement the permit program, subject to EPA approval, and by 1998 all states had complied. Permit fees will be assessed to pay for the program. Permit programs must include at least all CAA requirements applicable to each source, a schedule for compliance, and requirements for monitoring and reporting.