FEDERAL AIR TOXICS PROGRAM
USEPA PROGRAMS FOR AIR TOXIC EMISSIONS
Under the federal Clean Air Act Amendments of 1990, USEPA is required to adopt a number of national air toxic reduction programs that address 188 hazardous air pollutants, also known as HAPs. NJDEP works with USEPA to implement these programs in our state. Two of these programs are the adoption of Maximum Achievable Control Technology (MACT) standards for large sources (such as chemical manufacturing), and the Urban Air Toxics Strategy for small sources (such as hospital sterilizers). Once USEPA has issued all of the MACT standards, they are required to conduct a health risk assessment and revise a standard if it is shown to be necessary to protect public health. With the National-Scale Air Toxics Assessment (NATA), now known as AirToxScreen, USEPA has undertaken an effort to predict levels of hazardous air pollutants in outdoor air nationwide. This is described briefly below.
USEPA must promulgate regulations establishing emission standards for about 174 categories of HAP sources. The standards require the maximum degree of emission reduction that USEPA determines to be achievable for each particular source category. The standards are established for sources of HAPs that emit 10 tons per year of a single HAP or 25 tons per year of combined HAPs. Different criteria for MACT apply for new and existing sources. At the Administrator’s discretion, less stringent standards, known as generally available control technology (GACT) will be promulgated. To date, USEPA has promulgated 96 MACT emission standards. For more information on MACT, see “National Emission Standards for Hazardous Air Pollutants Information.”
Under the Clean Air Act, USEPA is required to develop and implement a program for assessing the risk remaining (known as “residual risk”) after facilities have implemented MACT standards. If necessary, USEPA is required to issue regulations to reduce any residual risks in order to protect public health with an ample margin of safety. USEPA must issue any risk-based regulations within eight years after it issues an air toxics standard for a given source category. In March of 1999, USEPA developed the Residual Risk Report to Congress which described the methods they would use to carry out the residual risk program. Using this guidance, on March 31, 2005, USEPA issued its first risk-based regulation for a promulgated MACT standard. To date, USEPA has promulgated residual risk standards for 16 source categories. For more information, see USEPA’s Air Toxics Web Page on Risk and Technology Review.
In July 1999, USEPA released the Integrated Urban Air Toxics Strategy. The strategy is a framework for addressing air toxics in urban areas from stationary, mobile, and indoor sources. The air toxics strategy has three main goals: 1) attain a 75% reduction in cancer risk attributable to large and small stationary sources, 2) attain a substantial reduction of public health risks posed by HAP emissions from area sources, and 3) address disproportionate impacts of air toxics hazards across urban areas such as geographic “hot spots,” highly exposed population subgroups, and predominately minority and low-income communities (See EPA Air Toxics Strategy Fact Sheet). As part of the strategy, USEPA has identified 30 air toxics that present the greatest threat to public health in urban areas. Also identified are 68 area source categories that contribute substantially to the emissions of these air toxics. Of those 68 categories, 53 have been regulated and the remaining are under development or will be developed in the future. For more information see USEPA’s Integrated Urban Air Toxics Strategy page.
Beginning in 2017, USEPA’s National-scale Air Toxics Assessment (NATA) became known as AirToxScreen. Like NATA, AirToxScreen estimates exposure for about 140 air toxics (or hazardous air pollutants/HAPs) throughout the country. Additionally, AirToxScreen includes a mapping tool that allows users to explore emissions, examine risk by air toxic or source type, and compare data on a national geographical scale.
AirToxScreen intends to identify air toxics of greatest potential concern and their characteristics. Results of AirToxScreen enable state, local, and tribal agencies including NJDEP to track trends of air toxics concentrations and make progress toward reducing risk from inhalation of ambient air toxics. USEPA emphasizes that AirToxScreen is best suited for analysis at a national, state, or county level rather than by census tract or neighborhood.
Further information about AirToxScreen can be found here.
Mobile sources, notably diesel trucks, are a significant source of air toxics. In 2007, USEPA’s proposed rule “Control of Hazardous Air Pollutants from Mobile Sources” was finalized. It significantly lowered emissions of air toxics by lowering the benzene content of gasoline, reducing exhaust emissions from passenger vehicles operated at cold temperatures, and reducing emissions from portable gasoline containers. Benzene is an air toxic and known human carcinogen. Mobile sources account for a majority of benzene emissions.
Initiatives to reduce diesel particulate emissions have also been implemented by USEPA. Diesel-related rulemakings by USEPA can be seen here.
For a historical overview of actions by USEPA to reduce air pollution from mobile sources, click here.
USEPA has carried out a national assessment of ambient concentrations of hazardous air pollutants (HAPs) and diesel particulate matter from stationary, area, and mobile sources for the years 1996, 1999, 2002, 2005, 2011, and 2014. This assessment, formerly known as NATA and conducted every three years, is now known as AirToxScreen and is conducted annually (since 2017). HAP emissions are then compiled in the National Emissions Inventory (NEI) every three years.
Using advanced dispersion models, USEPA uses the emissions estimates to predict ambient concentrations of HAPs and diesel PM for every census tract and county in the United States. These predicted concentrations are compared to ambient air toxic monitoring data to evaluate model accuracy. NATA also estimates exposure and evaluates the potential public health risks from inhalation of these air toxics by various populations. NATA/AirToxScreen is used to identify air toxics of greatest concern to public health, to track trends of air toxics concentrations over time, and to assist in prioritizing data collection activities.
For more information, refer to USEPA’s NATA webpage.