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National Air Toxics Assessment (1996 Data)

Release Date: 6/3/2002
Contact Information:
EPA 303-312-6005,

Release Date: 6/3/2002
Contact Information:
EPA 303-312-6043,

Release Date: 6/3/2002
Contact Information:
EPA 303-312-6434,

Release Date: 6/3/2002
Contact Information:
EPA 303-312-6603

What is the National Air Toxics Assessment (NATA)?

• As part of EPA's National Air Toxics Assessment (NATA) activities, EPA conducted a national-scale assessment of 33 air pollutants [a subset of 32 air toxics on the Clean Air Act's list of 188 air toxics, plus diesel particulate matter (diesel PM)]. NATA can be accessed on the web at: https://www.epa.gov/ttn/atw/nata

• Using data from 1996 (the most recent data available), NATA is an extensive effort to model chronic public exposure to outdoor air toxics emissions from the following sources: major, area, on-road, and non-road. These sources made up the national air toxics total of 1.1 million tons per year of 32 hazardous air pollutants (HAPs) and diesel PM. Note: 1) air toxics are frequently referred to as HAPs; and 2) indoor air quality is not part of or included in the NATA.

• The 1990 Cumulative Exposure Project (CEP) was EPA’s first attempt at an air toxics emission inventory. In 1999, the agency released the CEP with the following advisory statement: “EPA strongly cautions against using the results of this modeling exercise alone to draw real-world conclusions about current local conditions or to make regulatory decisions.”

• NATA consists of four segments: a source emissions inventory; an Assessment System Population Exposure Model (ASPEN), which is a dispersion modeling analysis of the emission inventory; a Health Assessment Population Exposure Model (HAPEM 4), which is a toxicological assessment of the data; and a public health risk assessment.

• NATA was submitted for review to the National Science Advisory Board (SAB) in 2001. The board provided EPA with extensive comments, which have been addressed.

• States, tribes and local governments were provided the opportunity to submit information for NATA and review it.


Background

• The 1990 Clean Air Act Amendments require EPA to reduce emissions and exposures to 188 specified hazardous air pollutants (HAPs). NATA includes these substances, but its focus is on 32 HAPs and diesel exhaust emissions.
• Air toxics emissions from major stationary sources, smaller (area sources), on-road (mobile), and non-road sources (trains, construction equipment, barges, airplanes, etc.) are regulated or addressed under the NATA program.


• The CAA requires that public exposures to cancer-causing HAPs be reduced by 75 percent and exposures to non-cancerous substances be reduced substantially below early 1990s levels. The target date for these reductions is 2010.


NATA (1996 data) limitations

• The emission inventory, although extensive, is incomplete. For example, military activities are not fully included in NATA.

• Air toxics data from the 48 continental states as well as Puerto Rico and the Virgin Islands are included in the 1996 NATA report. However, data from Alaska and Hawaii are not included.

• The SAB had extensive comments on improving ASPEN and the limitations of the HAPEM4 modeling.

• Modeled air toxics emissions figures tend to be lower than monitored results.

• Colorado presented information to correct errors in NATA data involving the state, especially regarding air emissions from mobile sources.

• 36 States, Puerto Rico and the Virgin Islands provided HAP emission inventory data for NATA.

• To be more practical, NATA data should be looked at as a whole entity, not in its individual segments, preferably at the state or county level. NATA contains data for 60,000 plus census tracks (about 4,000 people make up a census track; and a census track can be a small area 0.03 square kilometers up to 3084 square kilometers). EPA emphasizes that at local levels, NATA data should be used cautiously. NATA can serve as a planning or management tool, but should not be used for regulatory purposes.


What does the 1996 NATA reveal?

• Area and on-road HAP emissions are important contributors to the total HAP emissions in Region 8.

• All Region 8 States have benzene emissions that pose a cancer risk of one to 10 per million, except Utah which has a cancer risk of 10-20 per million.

• In addition to benzene, other HAPs such as 1,3-butadiene, formaldehyde, diesel PM, and carbon tetrachloride, pose cancer or elevated potential cancer risks in Region 8.

• Certain HAPs, such as hexachlorobenzene, ethylene dibromide, ethylene dichloride, manganese, and mercury were noted as being at elevated levels for several Region 8 States. HAPs from coke oven emissions in Utah posed concern.

• Yellowstone National Park in Teton and Park counties in Wyoming was noted as having air toxics concern. Teton county has no major air toxics sources, but area and non-road emissions are key contributors to these HAP emissions. Park county has air toxics emissions from major, area, on-road and non-road sources.

• Acrolein, a non-cancer HAP, posed concern in Region 8 and nationwide. Acrolein has commercial uses, comes from on-road and non-road sources, and emissions from wood fires.

• In general, population and industrial centers and transportation corridors have elevated air toxics modeled NATA data.

• There are 13 HAPs that have background levels that contribute to the nationwide cancer risk, for example benzene is one of these compounds. Overall EPA estimates that background levels pose a cancer risk of 20 per million people in Region 8.

• Changes have occurred as a result of EPA’s air toxics program. For example, as a result of planned emission control technology changes at a facility in Utah, the upcoming 1999 NATA results should reflect a lower total HAP emission in the State.

• Planned air toxics rules and new regulations on gasoline and diesel fuels starting in 2004 will help reduce HAP emissions.


The following table provides a simplified synopsis of the sources of HAPs emissions in Region 8 and the total yearly emissions in each state within the Region.

State	Major	Area	On-Road	Non-Road	Total HAP Emissions Million lbsyearly
CO	5	40	33	22	124.1
MT	22	34	21	15	64.5
ND	25	34	26	15	34.0
SD	12	28	35	25	27.7
UT	53	19	16	12	170.6
WY	36	27	18	19	59.0
Region 8 Total HAPs					479.9