1992-09-00 Air Toxics Update #8

This page last reviewed July 30, 2008


Air Toxics Update #8


This Update is the eighth in a series of publications summarizing recent activities in California's Air Toxics Program. It covers the Toxic Air Contaminant Identification and Control Program, the Air Toxics Hot Spots Assessment Program, and the Motor Vehicle Toxics Program. The seven previous Updates are available in the Air Resources Board (ARB) Public Information Office.


Below are the 18 substances which have been identified by the ARB as toxic air contaminants (TACs). Highlighted in red are the four compounds that were identified as TACs in the past 12 months, and a short discussion of these are in this update.

  • asbestos*
  • benzene*
  • cadmium
  • carbon tetrachloride
  • chlorinated dioxins / furans*
  • chloroform
  • ethylene dibromide
  • ethylene dichloride
  • formaldehyde
  • ethylene oxide*
  • hexavalent chromium*
  • inorganic arsenic
  • methylene chloride
  • trichloroethylene
  • vinyl chloride
  • nickel
  • perchloroethylene
  • 1,3-butadiene

Control decisions have been made for the eight TACs which are underlined above. A total of six air toxic control measures have been adopted for the five compounds marked with an asterisk. Two control measures have been adopted for hexavalent chromium. In developing air toxic control measures, the ARB incorporated pollution prevention practices whenever feasible. The six control measures, when fully in place and enforced, will affect over 2,000 sources statewide and will typically reduce toxic emissions from these facilities by at least 90 percent and in many cases as much as 99.9 percent.

Pollution Prevention -- the use of materials, processes, or practices to reduce, minimize, or eliminate the creation of pollutants or wastes. It includes practices that reduce the use of toxic or hazardous materials, energy, water, and/or other resources.

During the past 12 months, staff resources were directed towards implementing past control decisions as well as developing future control measures. The status of that work is discussed in this update. For information on air toxic control measures adopted in 1990 or earlier, please contact ARB's Public Information Office for previous editions of Air Toxics Updates.



At its August 1991 hearing, the Board identified nickel (metallic nickel and inorganic nickel compounds) as a TAC and determined it is a carcinogen without an identifiable threshold. The major source of ambient nickel emissions in California is fossil fuel combustion. Other sources include electroplating, cement manufacturing, municipal refuse and sewage sludge incineration, secondary smelting, and asbestos mining and milling.

California Environmental Protection Agency's Office of Environmental Health Hazard Assessment (OEHHA) estimate of the most plausible cancer risk from nickel is approximately 260 excess cancers per million people continuously exposed to 1 microgram per cubic meter. At ambient levels, this corresponds to an excess of 60 potential cancer cases for a California population of 30 million people exposed to average ambient concentrations over a 70-year lifetime. Hot spot exposures near fuel combustion facilities are likely to be about 10 times higher than average ambient concentrations.

Hot Spot -- An area where the concentration of air toxics is at a level where individuals may be exposed to an elevated risk of adverse health effects. Air toxics hot spots may include sources such as ethylene oxide sterilizers and chrome platers.


At its October 1991 hearing, the Board identified perchloroethylene as a TAC and determined it is a carcinogen without an identifiable threshold. Available information indicates that approximately 80 percent of perchloroethylene emissions result from the use of the solvent in dry cleaning and degreasing operations. Other sources of emissions include paints and coatings, adhesive formulations, distribution facilities, and solvent reclamation.

The OEHHA estimate of the most plausible cancer risk from lifetime exposure to 1 part per billion of perchloroethylene is approximately 40 excess cases per million people exposed. This represents an excess of about 450 potential cancer cases for a California population of 30 million people exposed to average ambient concentrations over a 70-year lifetime. The results of the hot spot and indoor concentration studies showed that individuals could be exposed to levels significantly above the ambient average.


At its March 1992 hearing, the Board identified formaldehyde as a TAC and determined it is a carcinogen without an identifiable threshold. Photochemical oxidation is the largest source (up to 90 percent) of formaldehyde concentrations in the outdoor ambient air. The largest sources of directly emitted formaldehyde are combustion of fuels, mobile sources, and process emissions from oil refineries.

Photochemical Oxidation -- A type of chemical reaction brought about by the radiant energy of the sun. The reaction of nitrogen oxides with oxygen in the presence of sunlight to form ozone is an example of photochemical oxidation. The products of this process contribute to photochemical smog.

The OEHHA estimate of the most plausible cancer risk from formaldehyde is approximately seven excess cancers per million people continuously exposed to 1 part per billion. At ambient levels, this corresponds to an excess of about 930 potential cancer cases for a California population of 30 million people exposed over a 70-year lifetime. Indoor exposure to formaldehyde is likely to be about ten times higher than average ambient concentrations. Building materials and other domestic products are the primary sources of formaldehyde emissions indoors.


At its July 1992 hearing, the Board identified 1,3-butadiene as a TAC and determined it is a carcinogen without an identifiable threshold. Fuel combustion from mobile sources makes up the largest proportion of direct outdoor emissions of 1,3-butadiene. 1,3-Butadiene reacts primarily with the hydroxyl radical during the day and the nitrate radical at night.

The OEHHA estimate of the most plausible cancer risk from lifetime exposure to 1 part per billion of 1,3-butadiene is approximately 370 excess cases per million people exposed. This represents an excess of 4,200 potential cancer cases for a California population of 30 million people exposed to average ambient concentrations over a 70-year lifetime.

Hot spot exposures to 1,3-butadiene may occur near synthetic rubber manufacturing facilities, petroleum refineries, stationary fuel combustion sources and resin and polymer production facilities using 1,3-butadiene. Limited indoor monitoring for 1,3-butadiene indicates that indoor levels of 1,3-butadiene, especially in the presence of heavy smoking, may be 20 times higher than outdoor levels.            


Toxic Metals

The ARB staff, with the participation of local air pollution control districts and affected industry, is developing a draft airborne toxic control measure for the control of arsenic, cadmium, and nickel emissions from non-ferrous metal-melting operations in California. Arsenic, cadmium and nickel are metals which have been identified by the ARB as TACs without identifiable threshold exposure levels. The measure, as proposed, will require the best available control technology for process emissions and contains pollution prevention elements to reduce fugitive emissions.

The proposed control measure, if adopted and implemented as currently written, will affect over 100 facilities statewide, and will cause an estimated 40 percent reduction of arsenic, cadmium, and nickel emissions from these sources. The control measure is tentatively scheduled to be considered by the Board in late 1992.

Lead is another metal being considered for identification as a TAC. Some non-ferrous metal melting facilities emit lead in addition to arsenic, cadmium, and nickel. Since the control technologies to reduce these metal emissions are the same, an additional benefit of the proposed control measure for non-ferrous metal melting is approximately a 50 percent reduction in lead emissions from these sources. Other sources of lead emissions will be evaluated for control upon the identification of lead as a TAC.


The ARB staff has evaluated and prioritized a number of perchloroethylene emission sources in California. Dry cleaners using perchloroethylene were selected for control measure development because of the large number of sources in the state and their proximity to people. In addition to commercial and industrial operations, dry cleaning is also performed at uniform supply companies, hotels, prisons, textile manufacturers, and military bases.

In developing the control measure for dry cleaners, the ARB staff is evaluating the potential public exposure to perchloroethylene emissions, assessing different types of dry cleaning processes, developing control strategies, and determining the potential economic impacts of various control options. A series of public consultation meetings are scheduled to give the affected industry and the public opportunities to participate in the development of the perchloroethylene dry cleaning air toxic control measure. The control measure is tentatively scheduled to be considered by the Board in early 1993.

Other Air Toxic Control Measure Efforts

The ARB staff is also evaluating several other source categories for possible control measure development such as halogenated solvent use in degreasing operations and paint stripping operations and the use of coatings containing chromate pigments. In addition, the staff is gathering information on sources of compounds not yet identified as TACs, such as acetaldehyde, benzo(a)pyrene, and lead.


At its October 1991 public hearing to identify perchloroethylene as a TAC, the Board directed the ARB staff to develop recommendations on how best to use risk assessment information for purposes of risk management. The Board asked the staff to work with industry, the local districts, other state agencies, and the affected public to identify options to assist risk managers in making decisions in light of the uncertainties inherent in risk assessments. The development of this risk management guidance has been an open process. During 1992, a continuing series of workshops will be held in various locations throughout the state to solicit ideas based on the needs of risk managers. The staff plans on presenting the Board with proposed guidance recommendations in early 1993.


Emission Inventory Reports

The Air Toxics Hot Spots Act phases facilities into the program over several years with larger facilities entering the process first. It is estimated approximately 3,400 facilities were required to submit emission inventories in the first reporting phase and 1,600 facilities in the second phase. Approximately 20,000 facilities are required to submit emission inventory information in the third phase of the program. Currently, all three phases of the program are in effect. The districts are required to review the emission inventory reports and ensure they comply with the Emission Inventory Criteria and Guidelines Regulation (California Code of Regulations Section 93300 et seq.) adopted by the ARB in 1989 and amended in 1990.

After the districts approve the reports, they must submit the reported data to the ARB for compilation into a statewide air toxics emission inventory. The ARB has developed the Air Toxics Emission Data System (ATEDS) to compile and maintain this information and to make it available to the public.

Once the emission data are transmitted to the ARB, they undergo quality assurance (QA) checks. The ARB staff is currently performing QA checks on first-phase facility data. Once the staff has completed the QA checks and corrected data are entered into the ATEDS, the data will be available for public use. The ARB anticipates having a significant portion of the emission data from first-phase facilities available in early 1993.

Under the "Hot Spots" program, facility operators are required to update their emission inventories every two years according to procedures specified in the Emission Inventory Criteria and Guidelines Regulation.

AB 2588 Facility Prioritization

Upon submission of emission inventory reports to the local districts, the emission data is reviewed by the districts to evaluate if a risk assessment should be prepared. This process is known as facility prioritization. As of January 1992, nearly all of the districts had selected a prioritization method and nearly 2900 facilities had been prioritized statewide. Approximately one quarter of these facilities were designated in the high priority category, requiring that risk assessments be prepared to quantify potential risks imposed by these facilities.

AB 2588 Risk Assessment and Public Notification

The California Air Pollution Control Officers Association (CAPCOA) Air Toxics "Hot Spots" Program Risk Assessment Guidelines were revised in January 1992. These guidelines provide assistance for the preparation of risk assessments required by AB 2588. A Health Risk Assessment computer program is also available which incorporates elements of the revised CAPCOA Risk Assessment Guidelines. Currently, staff of the ARB are working with CAPCOA to develop methodologies for public notification as required by AB 2588 for the communication of significant health risks. The CAPCOA Air Toxics "Hot Spots" Program Public Notification Guidelines are expected to be finalized by late 1992.


Reformulated Gasoline

In November 1991, the ARB approved new standards for gasoline; they will become effective in 1996. The properties limited by the new standards are:

  • the aromatic and olefinic hydrocarbons, sulfur, benzene, and oxygen contents;
  • the 50 percent and 90 percent distillation temperatures; and
  • the Reid vapor pressure (RVP).

With the exception of the limit on the benzene content, the standards were designed primarily to reduce levels of criteria pollutants (e.g., nitrogen dioxide and ozone). However, the standards will also reduce toxic emissions, primarily benzene and 1,3-butadiene. Some of the reduction of toxic emissions will occur as part of the general reduction of hydrocarbon emissions, and some will occur because the altered chemical make-up of the gasoline will lead to less formation of toxic compounds.

The total mass of toxic emissions from gasoline vehicles will be reduced by an estimated 25 percent. In terms of potential cancer incidence, this is equivalent to about 40 cases avoided per year over the period 1996 to 2010, about a 40 percent reduction of the potential cancer incidence that would be associated with emissions from gasoline vehicles.


Compounds expected to be considered for identification by the Board during the next 12 months include acetaldehyde, benzo(a)pyrene, and lead. During this same period, control measures for perchloroethylene and toxic metals are scheduled to be considered by the Board. For further information about ARB's TAC program, please contact:

Air Resources Board
Stationary Source Division
P.O. Box 2815
Sacramento, CA 95812
(916) 445-0650


Air Toxics Updates