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Section 112(k) - Urban Air Toxics Program Development of Air Emissions Inventory

WHAT IS SECTION 112(k)?

Under sections 112(c)(3) and 112(k) of the Clean Air Act as amended in 1990, the Environmental Protection Agency (EPA) is required to identify categories and subcategories of sources of hazardous air pollutants (HAPs) in urban areas that pose a threat to human health. Specifically, the EPA must identify sources of at least 30 HAPs that present the greatest threat to urban populations, and assure that sources that account for 90 percent or more of the aggregate emissions are subject to regulation. In addition, a national strategy must be developed to reduce cancer incidence attributable to these pollutants by at least 75 percent.

Specific provisions of sections 112(c)(3) and 112(k) include:

Section 112(c)(3): ...The Administrator shall, not later than November 15, 1995, and pursuant to subsection (k)(3)(B) of this section, list, based on actual or estimated aggregate emissions of a listed pollutant or pollutants, sufficient categories or subcategories of area sources to ensure that area sources representing 90 percent of the area source emissions of the 30 hazardous air pollutants that present the greatest threat to public health in the largest number of urban areas are subject to regulation under this section. Such regulations shall be promulgated not later than November 15, 2000.
Section 112(k): ...The Administrator shall prepare a strategy not later than November 15, 1995, that identifies not less than 30 hazardous air pollutants which, as a result of area sources, present the greatest threat to public in the largest number of urban areas.... and assure that sources accounting for 90 percentum or more of the aggregate emissions of each of the 30 are subject to regulation. Also, EPA is required to reduce cancer risk attributable to these pollutants by 75 percent.

In order to respond to these mandates, EPA performed an analysis of the most significant HAPs in urban areas.

To determine "the 30 HAPs that present the greatest threat to public health", as required in section 112(c)(3), a method of comparing the emissions and relative health threat of all 188 HAPs listed in section 112 is necessary. Unfortunately, as stated in the EPA's Urban Area Source Research Program - A Status Report on Preliminary Research, fair or better information to perform such a risk analysis exists for only 20 or so of the 188 HAPs. Therefore, a risk-based comparison of all 188 HAPs is not possible at this time. In lieu of such a comparison, a qualitative analysis of existing information can be made to exhibit what is known about each HAP in terms of monitored air concentrations, emissions inventories, and health hazards. This represents the best available information and highlights consistent findings, in terms of HAPs with significant evidence of problems, and uncertainties. Because this analysis is a composite of information from a variety of local- and national-scale studies, its usefulness in determining specific actions to reduce such emissions and relative hazards on a national scale may be limited.

Available toxicity, ambient air monitoring, and emissions inventory data, and results from existing exposure and risk assessment studies were used to develop a list of 40 potential HAPs. (See Table 1). The list of HAPs presented in Table 1 is not considered to be the final list, but rather is considered a starting point for the focus of further analysis under the urban air toxics program.

Table 1. List of Potential 112(k) HAPs.
CAS Number Name CAS Number Name
79345 1,1,2,2-tetrachloroethane 140885 Ethyl acrylate
79005 1,1,2-trichloroethane 106934 Ethylene dibromide (dibromoethane)
78875 1,2-dichloropropane (propylene dichloride) 75218 Ethylene oxide
106990 1,3-butadiene 107062 Ethylene dichloride (1,2-dichloroethane)
542756 1,3-dichloropropene 50000 Formaldehyde
106467 1,4-dichlorobenzene 302012 Hydrazine
75070 Acetaldehyde   Lead compounds
107028 Acrolein   Manganese compounds
79061 Acrylamide   Mercury compounds*
107131 Acrylonitrile 74873 Methyl chloride (chloromethane)
  Arsenic compounds 75092 Methylene chloride (dichloromethane)
71432 Benzene 101688 Methylene diphenyl diisocyanate (MDI)
  Beryllium compounds   Nickel compounds
117817 Bis(2-ethylhexyl)phthalate (DEHP)   Polycyclic organic matter*
  Cadmium compounds 91225 Quinoline
56235 Carbon tetrachloride 100425 Styrene
67663 Chloroform 127184 Tetrachloroethylene (perchloroethylene)
  Chromium compounds 79016 Trichloroethylene
  Coke oven emissions 75014 Vinyl chloride
  Dioxins/furans* 75354 Vinylidene chloride (1,1-Dichloroethylene)
* These HAPs are also 112(c)(6)-listed HAPs. The emissions estimates for these HAPs have already been completed.

Inventory Development for Table 1 HAPs

In order to address the requirements of sections 112(c)(3) and 112(k), national emissions inventories of HAPs were developed. These inventories serve as the reference baseline in the development of a national strategy to control the 112(k) pollutant emissions.

EPA reviewed and analyzed available data to revise existing assessments of the sources in the U.S. that emit each HAP listed in Table 1. Inventories for Table 1 HAPs that are listed in section 112(c)(6) have already been compiled and were revised. The final 112(c)(6) inventory report is posted on the 112(c)(6) web page. EPA compiled existing emissions information from a variety of efforts - regulatory development, Locating and Estimating documents, Toxic Release Inventory (TRI), State and Local air agencies, and industry trade associations. The approaches used in compiling the emissions inventory for each pollutant and source category are documented. The quantities and percentages of emissions attributable to each source category are also documented including those emissions associated with area sources per the section 112(a) definition and considering co-located sources. The nominal base year for developing emissions data is 1990. The inventories provide major (point), area, and mobile source estimates for each Table 1 HAP. The inventories are allocated to provide an estimate of urban vs. rural emissions and major vs. area source category emissions.

EPA produced a draft inventory report that was posted for internal and external review on September 1, 1997. The review period was six weeks and ended in October 1997. An interim inventory was prepared. In September 1998, an urban stratgy was proposed in the Federal Register. The interim inventory was posted with Federal Register notice for review. A summary of comments is posted.

The final 112(k) inventory is found in the following files. These files are in Adobe Acrobat® PDF format. (In order to view and print the files you must have the Adobe Acrobat® Reader appropriate for your hardware and operating system.)

Title Notes File Size
Summary of Public Comments Related to the Emission
Inventory Associated With the Urban Air Toxics Strategy
  47 KB
1990 Emissions Inventory or Forty Potential Section
112(k) Pollutants
Final Report- main document 1.7 MB
Appendices A - F   2.3 MB

These inventories served as the reference baseline in the development of a national strategy to control the 112(k) pollutant emissions. OAQPS used these emissions estimates to determine the universe of anthropogenic emissions of Table 1 pollutants and to identify source categories emitting those HAPs already subject to regulation. Detailed source category emissions and monitoring data of the Table 1 HAPs were merged to form a consistent source category data file. This file formed the basis for a number of measures that assisted EPA in the following ways:

  • Establish the top 30 (or more) HAPs.
  • Identify additional source categories which should be listed in order to achieve the goals of subsection 112(k).
  • Determine which source categories will be addressed by MACT, GACT, residual risk standards, or other measures.
  • Establish a baseline from which progress toward meeting the goal of assuring that 90% or more of the aggregate emissions of each of the identified HAPs are subject to standards pursuant to subsection (d).
  • Evaluate progress toward the 90% goal referred to above.
  • Evaluate progress toward the goal of reducing the incidence of cancer attributable to exposure to hazardous air pollutants from all stationary sources of not less than 75%.

Proposed Definition of Urban/Rural for Urban Area Source Program

Sections 112(k) and 112(c)(3) of the 1990 Clean Air Act (CAA) Amendments require the U.S. Environmental Protection agency (EPA) to identify categories and subcategories of sources of hazardous air pollutants (HAPs) in urban areas that pose a threat to human health. Specifically, the EPA must identify area sources of at least 30 HAPs that present the greatest threat to urban populations, and assure that sources that account for 90 percent or more of the aggregate emissions are subject to regulation. In addition, a national strategy must be developed to reduce cancer incidence attributable to these HAPs by at least 75 percent.

The statutory language in Section 112(k) requires the identification of HAPs that are presenting a public health threat in urban areas. However, the CAA does not provide a definition of "urban". Urban areas with populations greater than 250,000 are singled out for air monitoring; however, the possibility of monitoring other urban areas is also mentioned.

To spatially allocate emissions on an urban and rural basis, Bureau of the Census statistical data were used. The Bureau of the Census has designated urban and rural areas within every county in the United States. The criteria used include population density and total population. Using population data and urban/rural designations for 1990, every county in the United States was classified as one of the following categories:

  • Urban-1 (U1) counties which include a metropolitan statistical area (MSA) with a population greater than 250,000;

  • Urban-2 (U2) counties that do not include a MSA with a population greater than 250,000, but the Bureau of the Census designates more than 50 percent of the county population as "urban." These counties include areas which comprise one or more central places and adjacent densely settled surrounding urban fringe. The urban fringe consists of continguous territory having a density of at least 1,000 persons per square mile.

  • Rural (R) counties that do not include a MSA with a population greater than 250,000, and the Bureau of the Census designates more than 50 percent of the county population as "rural."

If any part of a county contained an Urban-1 area, then the whole county was classified as Urban-1. For all remaining counties, if greater than 50 percent of the population was classified as rural, then that county was cosidered Rural. Counties not designated as Urban-1 or Rural were classified as Urban-2. The Urban-1 and Urban-2 counties were combined and are listed as urban.

A table listing counties by state, their 1990 Census data and resulting Urban/Rural classification is available in Adobe Acrobat® format: Urban/Rural Census Data & Classification.

FOR MORE INFORMATION...

Comments regarding emissions inventory and any emissions information should be directed to:

Ms. Anne Pope, Emission Factor and Inventory Group, U.S. EPA, Mail Drop 14
Research Triangle Park, North Carolina, 27711
Phone: (919)541-5373
E-mail: POPE.ANNE@EPA.GOV

Comments or questions regarding policy should be directed to:

Ms. Laura McKelvey, Visibility and Ecosystem Protection Group, U. S. EPA, Mail Drop 15
Research Triangle Park, North Carolina, 27711
Phone: (919)541-5497
E-mail: MCKELVEY.LAURA@EPA.GOV

For assistance with downloading files, call the Info CHIEF Help Desk at (919)541-5285.

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