Overview of the Air Toxics "Hot Spots" Information and Assessment Act

This page last reviewed August 17, 2016


The Air Toxics "Hot Spots" Information and Assessment Act (AB 2588, 1987, Connelly) was enacted in September 1987. Under this, stationary sources are required to report the types and quantities of certain substances their facilities routinely release into the air. Emissions of interest are those that result from the routine operation of a facility or that are predictable, including but not limited to continuous and intermittent releases and process upsets or leaks.

The goals of the Air Toxics "Hot Spots" Act are to collect emission data, to identify facilities having localized impacts, to ascertain health risks, and to notify nearby residents of significant risks. In September 1992, the "Hot Spots" Act was amended by Senate Bill (SB) 1731 (Calderon) to address the reduction of significant risks. The bill requires that owners of significant-risk facilities reduce their risks below the level of significance.

The Act requires that toxic air emissions from stationary sources (facilities) be quantified and compiled into an inventory according to criteria and guidelines developed by the ARB, that each facility be prioritized to determine whether a risk assessment must be conducted, that the risk assessments be conducted according to methods developed by the Office of Environmental Health Hazard Assessment (OEHHA), that the public be notified of significant risks posed by nearby facilities, and that emissions which result in a significant risk be reduced. Since the amendment of the statute in 1992 by enactment of SB 1731, facilities that pose a potentially significant health risks to the public are required to reduce their risks, thereby reducing the near-source exposure of Californians to toxic air pollutants. Owners of facilities found to pose significant risks by a district must prepare and implement risk reduction audit and plans within 6 months of the determination.

The Air Resources Board (ARB) is required to develop a program to make the emission data collected under the "Hot Spots" Program available to the public. If requested, districts must make health risk assessments available for public review. Districts must also publish annual reports which summarize the health risk assessment program, rank facilities according to the cancer risk posed, identify the facilities posing non-cancer health risks, and describe the status of the development of control measures.

The "Hot Spots" Program has complemented the ARB's existing air toxics identification and control programs. It has located sources of substances not previously under evaluation, and it has provided exposure information necessary to prioritize substances for control measures and develop regulatory action. Also, the preparation of the "Hot Spots" emission inventory made facility owners aware of their toxics problems. As a result, facilities have taken voluntary steps to reduce emissions of air toxics. Limited district and facility surveys have identified voluntary reductions of over 1.9 million pounds per year in the emission of air toxics from just 21 facilities in California. The benefits that come from this type of action are less risk to workers and to the public, reduced operation costs, demonstration of emission reduction options for other sources, and improved community relations.

The Act was further modified by AB 564, chaptered on September 19, 1996. The passage of AB 564 amended the Hot Spots statute in several ways, including adding provisions that: exempt specified low priority facilities from further compliance with the Hot Spots program; reinstate exempted facilities if specified criteria are met; specify an alternative evaluation process for facilities subject to district permit programs; and other changes to exempt specified facilities from further compliance with the Hot Spots Program.


The Air Toxics "Hot Spots" Act requires the ARB to compile and maintain a list of substances posing chronic or acute health threats when present in the air. The Air Toxics "Hot Spots" Act currently identifies by reference over 600 substances which are required to be subject to the program. The ARB may remove substances from the list if criteria outlined in the law are met. A facility is subject to the Act if it: (1) manufactures, formulates, uses, or releases a substance subject to the Act (substance which reacts to form such a substance) and emits 10 tons or more per year of total organic gases, particulate matter, nitrogen oxides or sulfur oxides; (2) is listed in any district's existing toxics use or toxics air emission survey, inventory or report released or compiled by a district; or (3) manufactures, formulates, uses, or releases a substance subject to the Act (or substance which reacts to form such a substance) and emits less than 10 tons per year of criteria pollutants and is subject to emission inventory requirements.

The Air Toxics "Hot Spots" Act requires facilities meeting the applicability criteria to prepare air toxics emission inventory plans and, subsequently, emission inventory reports. The Emission Inventory Criteria and Guidelines Report, which was first approved by the ARB in April 1989, provides specifications for acceptable emission inventory plans and reports, and inventory updates. Portions of the Guidelines were amended by the ARB in June 1990, September 1990, June 1991, and again in June 1993. AB 1060, which became effective January 1, 1994, changed the update period from every two to every four years. The Guidelines, which were approved by the State Office of Administrative Law on January 31, 1994, incorporate the changes in update procedures mandated by AB 1060. In May 1996, the Board approved a proposal to re-codify the Emission Inventory Criteria and Guideline Report. The recodification restructured the Guidelines so that there is only one numbered section in the California Code of Regulations which would incorporate by reference, the entire Guidelines as a document entitled the "Emission Inventory Criteria and Guidelines Report."

In July 1997, the Board approved additional amendments to the Emission Inventory Criteria and Guidelines Report. These amendments significantly streamlined the inventory updating process by placing most of the updating requirements on high risk facilities. The Guidelines have since been modified in part to conform with current legislation. The modified version was available in draft form for public comment from February 6, 1997 to February 21, 1997. The Guidelines were approved by Office of Administrative Law and became effective July 1, 1997.

Facility operators must submit to the district a proposed emission inventory plan indicating how emissions will be measured or calculated. The district must approve, modify, or return the inventory plan to the operator for revisions within 120 days. Once a district approves a plan, the facility operator must implement the plan and submit the emission inventory to the district within 180 days. For certain classes of facilities, districts must prepare industrywide inventories and individual facility reports are not required. Districts will determine which facilities will be covered by industrywide inventories based on conditions such as economic hardship and small business status.

Facilities subject to the "Hot Spots" Program were phased in according to their criteria pollutant emissions. Facilities emitting 25 tons per year or more of total organic gases, particulate matter, nitrogen oxides, or sulfur oxides and using, manufacturing, formulating, or releasing a listed substance were required to submit inventory plans by August 1, 1989. Facilities listed on a district's toxics inventory, survey, or report as of a specified date were also required to submit plans by August 1, 1989. These are considered Phase I facilities.

Facilities emitting between 10 and 25 tons per year of criteria pollutants (Phase II facilities) and using, manufacturing, formulating, or releasing a substance covered by the program, were required to submit plans by August 1, 1990.

Facilities within specified source categories which emit less than 10 tons per year of criteria pollutants (Phase III facilities) and which use, manufacture, formulate, or release a listed substance were required to submit plans by August 1, 1991, unless notified by the district that they were included in an industrywide emission inventory.

Inventory reports are due within 180 days of district approval of the emission inventory plan. Emission inventory reports for Phase I facilities were due to the district as early as June 1, 1990. Emission inventory reports for Phase II facilities were due to the district as early as June 1, 1991, and for Phase III facilities as early as June 1, 1992.

Facilities subject to the program must also update their emission inventories every four years. This insures that facility information is kept current in the database. The update requirements were streamlined in June 1993, and are now based on each facility's prioritization category. The new update requirements substantially reduce reporting requirements for all but the significant risk facilities, those required to notify under this program, and exempt low risk facilities.

The ARB maintains the toxics emissions data in the Air Toxics Emission Inventory Data System (ATEDS) and the data is available upon request. To place industrial facility air toxic emissions into perspective, the ARB was required to compile emission inventory data for mobile, natural, and area sources not subject to district permit requirements. These data are also available upon request.

After reviewing emission inventory data, districts must rank facilities for purposes of risk assessment into high, intermediate, and low priority categories. The categorization of facilities into priority groups was to be completed by December 1, 1990, for facilities required to submit emission inventory plans by August 1, 1989, by December 1, 1991 for facilities required to submit plans by August 1, 1990, and by December 1, 1992, for facilities required to submit plans by August 1, 1991. Facilities will be re-prioritized if their inventory update shows any significant changes.

In establishing priorities, the district is to consider the potency, toxicity, quantity, and volume of hazardous materials released from the facility, the proximity of the facility to potential receptors, and any other factors that the district determines may indicate that the facility may pose a significant risk. The district is required to hold a public hearing prior to the final establishment of priorities and categories.

The California Air Pollution Control Officers Association (CAPCOA) has developed Air Toxics "Hot Spots" Program Facility Prioritization Guidelines to assist districts in implementing the law's prioritization provisions. The purpose of the guidelines is to provide districts with suggested procedures for use in prioritizing facilities. The guidelines are available to those districts who choose to use them. However, districts may develop and use prioritization methods which differ from the CAPCOA guidelines. Originally developed in 1990, in 2016 the Facility Prioritization Guidelines were updated and can be found on the CAPCOA website at www.capcoa.org.

Within 150 days of the designation of priorities, the operator of every facility that has been included within the highest priority category must prepare and submit to the districts a health risk assessment. A risk assessment, as defined under the Air Toxics "Hot Spots" Act, includes a comprehensive analysis of the dispersion of hazardous substances into the environment, the potential for human exposure, and a quantitative assessment of both individual and population wide health risks associated with those levels of exposure. The district may grant a 30-day extension for submittal of the risk assessment. The risk assessments are reviewed by the district and OEHHA. In addition, the district may require facilities in the intermediate and low priority categories to also submit a health risk assessment.

In 1993, CAPCOA developed Air Toxics "Hot Spots" Program Risk Assessment Guidelines. The purpose of these guidelines is to provide procedures for use in preparing health risk assessments required under the Air Toxics "Hot Spots" Act. However, districts may develop and use risk assessment methods which differ from the CAPCOA guidelines. On March 6, 2015, the Office of Environmental Health Hazard Assessment (OEHHA) finalized the OEHHA Guidance Manual (Guidance Manual).  This Guidance Manual supersedes the 1993 CAPCOA Risk Assessment Guidance.  The Guidance Manual is built on a foundation of three public and peer-reviewed Risk Assessment Guidelines documents, finalized in 2008, 2009, and 2012.  These three documents focused on non-cancer risk, cancer risk, and exposure assessment, respectively.  The Guidance Manual and the three underlying foundational documents are designed to improve estimates of potential lifetime cancer and non-cancer risks from air toxics by refining exposure data for individuals of all ages, and with adjustments based on new science about the increased childhood sensitivity to air toxics. 

The CAPCOA developed two industry-wide risk assessment procedures. The purpose of these industry specific assessments is to assist both the districts and facilities with the emission inventory and risk assessment requirements of the "Hot Spots" program.

The two industries covered by the industry-wide assessments are: auto bodyshops and gasoline service stations. Facilities which meet a specific set of requirements outlined in the law are candidates for an industry-wide assessment. The requirements are focused on small businesses that are from the same industrial class, where individual compliance would impose severe economic hardships, and where emissions are easily and generically characterized.

Once risk assessments are reviewed by OEHHA and approved by the districts, facility operators must notify all exposed persons of the risk assessment results if the district determines that there is a potentially significant health risk associated with emissions from the facility.

The CAPCOA Toxics Committee has also developed Public Notification Guidelines. The purpose of these guidelines is to assist districts in developing their public notification procedures. Once again, districts may choose to follow different procedures than those provided in the CAPCOA guidelines. A more detailed description of the procedures can be found in the CAPCOA Air Toxics "Hot Spots" Program Public Notification Guidelines, October 1992.

The CAPCOA Prioritization Guidelines and Public Notification Guidelines are available from CAPCOA or the ARB. The CAPCOA Risk Assessment Guidelines are available from CAPCOA. For more information please call or email Alan Abbs, Executive Director of CAPCOA, at (916) 441-5700 or Greg Harris of the ARB at (916) 327-5635.

SB 1731, which amends the "Hot Spots" Program, adds two major elements to the program. First, OEHHA is required to adopt risk assessment guidelines for the program using a full public review process. OEHHA is currently developing these new guidelines and anticipates adoption by the end of 1997. Second, facilities determined to have a significant risk must conduct an airborne toxic risk reduction audit and develop a plan to implement airborne toxic risk reduction measures. The audit and plan must be submitted to the district within 6 months of the determination. It must describe the risk reduction methods the facility will use to reduce its risk below the level of significance within 5 years; however, the district may shorten or lengthen the time period (up to 5 additional years) under certain conditions.

Under SB 1731, the ARB is required to provide assistance to smaller businesses for developing and applying risk reduction techniques. As part of that assistance, the ARB is developing guideline documents on how to conduct an audit, including a self conducted checklist for certain industries. The ARB is developing a General Guideline document that can be used by any facility required to conduct an audit and plan. In addition, the ARB is developing guideline documents for six different source categories: autobody refinishing, chrome plating, aerospace operations, degreasing operations, service stations, and dry cleaners. All of these documents are expected to be completed by the end of 1997.

The Air Toxics "Hot Spots" Act prescribes penalties for failure to comply with the Act or for knowingly submitting false information. Depending on the violation, civil penalties range from $500 to $25,000 for each day the infraction remains uncorrected. SB 1731 also penalizes for noncompliance. It specifies that the facility operator is subject to civil penalties for failure to submit a complete audit and plan or failure to implement the measures set forth in the plan.


The Air Toxics "Hot Spots" Act requires that the ARB develop and adopt a fee regulation which recovers the state costs to implement the program. The regulation also requires each district to adopt a fee schedule which recovers the costs to the district. Each district is responsible for billing and collecting fees from all facilities subject to the Act and for remitting the district's share of the state costs to the ARB. The Act provides administrative penalties, to be assessed on facilities, in cases where fees are not paid to the district with 60 days of receipt of the notice.

Because the air toxics inventories required under the "Hot Spots" Act were not developed when the Act became effective, the fees were primarily based on criteria pollutant emissions. However, now that the inventories are more complete, SB 1378 (McCorquodale, 1992) requires that fees be based on toxic emissions and facility risk priority to the extent possible. To conform with SB 1378, ARB staff developed a new method for distributing the State's cost among districts and for calculating fees for fiscal year 1996-97. In the new method, fee categories are based on prioritization scores and health risk assessment results. Generally, fee rates increase with increasing risks. In fiscal year 2001-2002, the ARB converted the fee regulation into an administrative process which freezes the State fees at 2001-2002 levels. If it becomes necessary to make substantive changes to the fee regulation (change the fee rates), the ARB staff will return to the Board to amend the regulation.

Legislation (AB 564) was passed in September 1996 to amend the Hot Spots provisions in the Health and Safety Code. This bill includes exemption thresholds from the Program and the Fee Regulation. The primary impact of AB 564 on the Fee Regulation was the exemption of many lower risk facilities (with priority scores greater than one but less than or equal to ten) from paying State fees. These exemptions were incorporated into the Fee Regulation.


In summary, the Air Toxics "Hot Spots" Act establishes a formal air toxics emission inventory risk quantification program for districts to manage. The goal of the Air Toxics "Hot Spots" Act is to collect emission data indicative of routine predictable releases of toxic substances to the air, to identify facilities having localized impacts, to evaluate health risks from exposure to the emissions, to notify nearby residents of significant risks, and, due to SB 1731, reduce risk below the determined level of significance. Information gathered from this program has complemented the ARB's existing toxic air contaminant program by locating sources of substances that were not under evaluation and by providing exposure data needed to develop regulations for control of toxic pollutants. Additionally, the program has been a motivating factor for facility owners to voluntarily reduce their facility's toxic emissions.

For more information on fees or the emission inventory provisions of the Air Toxics "Hot Spots" Program, click the Contact Us on this page. For information on prioritization, risk assessment, and notification, please call or email Robert Krieger, Manager, Emissions Evaluations Section, at (916) 323-1202. For more information on the new OEHHA risk assessment guidelines, please call or email Dr. John Budroe, Chief, Air Toxicology and Risk Assessment Section, Office of Environmental Health Hazard Assessment, at (510) 622-3145.