1989-06-00 Air Toxics Update #5

This page last reviewed July 30, 2008


Air Toxics Update #5




This Update is the fifth in a series of publications on California's Air Toxics Program. It provides an updated compound review, a description of air toxics control actions considered by the Air Resources Board (ARB) during 1988, and a brief preview of future air toxics activities.

For anyone wanting a general description of California's air toxics law and how the program works, Air Toxics Program Update #1 is recommended. For a discussion of the startup of the program and a description of the three substances identified as toxic air contaminants (TACs) in 1985 -- benzene, ethylene dibromide, and ethylene dichloride -- please see Update #2. For those TACs identified in 1986 -- hexavalent chromium, asbestos, and chlorinated dioxins / furans -- please see Update #3. For a description of TAC identification occurring in 1987 -- cadmium, carbon tetrachloride, and ethylene oxide -- see Update #4. Update #3 describes control decisions for benzene and ethylene dibromide. Control decisions for benzene and ethylene dichloride are described in Update #4.


During 1988 there were 15 compounds at various stages in the review process. Substances identified as toxic air contaminants that moved into or were already in the control measure phase are:

  • asbestos
  • benzene
  • cadmium
  • carbon tetrachloride
  • chlorinated dioxins/furans
  • hexavalent chromium
  • ethylene oxide

Those substances in the identification phase at the end of 1988 are:

  • methylene chloride
  • inorganic arsenic
  • vinyl chloride
  • chloroform
  • formaldehyde
  • nickel
  • perchloroethylene
  • trichloroethylene


The ARB considered control of three TACs in 1988 -- benzene, carbon tetrachloride, and hexavalent chromium. The Board took action on benzene and hexavalent chromium, and decided not to pursue further control of carbon tetrachloride at the present time.


In 1985, the ARB identified benzene as a toxic air contaminant with no identifiable threshold exposure level. In October 1987, the Board adopted the first control measure for benzene, a measure requiring the installation of Phase I and II vapor recovery systems at retail service stations throughout the state. This measure will reduce the individual fueling risk and the total statewide cancer risk from service station benzene emissions by 85 percent. The measure is described in Air Toxics Update #4.

In July 1988, the Board adopted an advisory suggesting that local districts consider requiring greater availability of hold-open latches on gasoline-dispensing nozzles. A hold-open latch is a device which allows for the hands-off refueling of a vehicle. The use of a hold-open latch in conjunction with a vapor recovery nozzle can further reduce personal exposure to benzene during refueling by as much as 75 percent.      

A proposed regulation to limit the benzene content of gasoline to 0.8 volume percent is being evaluated as part of an integrated motor vehicle/fuels control strategy.

Carbon Tetrachloride

In 1987, the Air Resources Board identified carbon tetrachloride as a toxic air contaminant without an identifiable threshold exposure level. The Board considered and approved the carbon tetrachloride control plan in December 1988.

Since the time carbon tetrachloride was identified as a toxic air contaminant, statewide emissions have decreased considerably. The major sources of carbon tetrachloride emissions in California, carbon tetrachloride production and chlorofluoro-carbon manufacturing, have been voluntarily controlled through the application of best available control technology. Carbon tetrachloride was formerly used as a grain fumigant, but the Environmental Protection Agency has cancelled the registration of grain fumigants containing carbon tetrachloride. Emissions from these three sources are now less than 10 percent of their previous levels.

Carbon tetrachloride's atmospheric chemistry is described in Air Toxics Update #4. Because of its long atmospheric lifetime of 50 to 100 years, emissions of carbon tetrachloride have accumulated to produce a relatively uniform global background concentration. With the recent control of the major California sources of carbon tetrachloride, exposure to the global background concentration now poses a far greater risk than emission sources within the State.

Based on the above factors, the ARB decided not to pursue further control of carbon tetrachloride at this time. However, the ARB staff will continue to keep abreast of carbon tetrachloride uses and emissions and will propose control measures if there is an increased threat to public health.

Hexavalent Chromium

In January 1986, the Air Resources Board identified hexavalent chromium as a toxic air contaminant and listed it as a substance without an identifiable carcinogenic threshold. The uses, emissions, and health risks associated with hexavalent chromium are described in Air Toxics Update #3. The hexavalent chromium control plan was approved by the Board in February 1988, concurrent with the adoption of the first control measure for hexavalent chromium: a measure to reduce emissions from chrome plating and chromic acid anodizing operations.

This control measure requires small, medium, and large hard plating or anodizing shops to achieve either a 95, 99, or 99.8 percent reduction of uncontrolled emissions, respectively, or to emit hexavalent chromium at a rate of less than .15, .03, or .006 mg/amp-hour, respectively. Decorative plating shops must achieve at least 95 percent control, which can be accomplished by maintaining a foam blanket or a mist suppressant in their plating tanks to minimize emissions. Up to 99 percent control for hard plating shops can be achieved using technology familiar to and demonstrated in the plating industry. The 99.8 percent control requirement has not been achieved at plating shops and requires the transfer of control technology from other industries and possibly the modification of plating process parameters.

Consequently, the ARB staff and the chrome plating industry are conducting a demonstration project to determine the feasibility of achieving either 99.8 percent control or an emission rate of .006 mg/amp-hour at hard plating shops.

Control of chrome plating and anodizing emissions will reduce the statewide cancer incidence from exposure to these sources of hexavalent chromium by approximately 97 percent. The measure will also reduce the statewide cancer incidence from exposure to all sources of hexavalent chromium by over 50 percent.

A control measure for emissions of hexavalent chromium from chromate treated cooling towers is being considered. The measure will be described in the next Air Toxics Update.


Air Toxics "Hot Spots"

In September 1987, AB 2588 (H&S Code 44300 et seq.), the Air Toxics "Hot Spots" Information and Assessment Act, was signed into law. Generally, the purpose of the law is to compile a statewide comprehensive air toxics emissions inventory. Information reported under this program will be useful in ARB's TAC identification and control program. Emission inventory plans are to be submitted to local air pollution control districts in the Fall of 1989.

Integrated Motor Vehicle / Fuels Control Strategy

Two bills were adopted by the state legislature in 1988, each requiring the ARB to define its regulatory agenda for motor vehicles and fuels within a broader framework. Instead of using a piecemeal approach -- moving forward regulation by regulation -- the ARB is employing an integrated approach toward controlling motor vehicle emissions and fuels.

The California Clean Air Act (AB 2595), effective January 1, 1989, states that the ARB shall:

"adopt standards and regulations which result
  in the most cost-effective combination of
  control measures on all classes of motor
  vehicles and motor vehicle fuel..."


AB 4392 (H&S Code 39663, 39667), calls for the ARB to adopt a broader approach in reducing motor vehicle toxic emissions and clarifies the ARB's authority to control multiple toxic air contaminants simultaneously with an overall emission control strategy.

In light of this legislative direction, the ARB is continuing to implement the benzene control plan (described in Air Toxics Update #3). The benzene control plan directs the ARB staff to continue to develop control measures, including motor vehicle controls, as part of the ARB's overall efforts to reduce hydrocarbon emissions. As an example, the control measures in the "Post 1987 Motor Vehicle Plan" approved by the Board will concurrently reduce emissions of hydrocarbons and benzene. In addition, AB 4392 requires a report to the Board about the overall risks of toxic emissions from motor vehicles -- a necessary first step for the ARB's new integrated approach.

With the authority and direction provided by the new legislation, the ARB is planning to devote significant resources to developing the most cost-effective package of emission control measures for motor vehicles and fuels. The goal is to achieve maximum reductions of ozone precursors, benzene, and other toxic air contaminants, for the least overall cost to society.

Additional Air Toxic Plans

During the next 12 to 15 months, the Board is expected to consider identification of methylene chloride, inorganic arsenic, and vinyl chloride as TACs. For more information about the current status of compounds in the identification process, please contact:

Chief, Air Quality Measures Branch
Stationary Source Division
Air Resources Board
P.O. Box 2815
Sacramento, CA 95812
(916) 322-7072

The Board is expected to consider control measures for hexavalent chromium, dioxins, asbestos, and ethylene oxide in the next 12 to 15 months. For more information about the current status of compounds in the control development process, please contact:

Chief, Emissions Assessment Branch
Stationary Source Division
Air Resources Board
P.O. Box 2815
Sacramento, CA 95812
(916) 322-6023

Air Toxics Updates