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Air Toxics

What is the Air Toxic "Hot Spots" Act?

California enacted the Air Toxics Hot Spots Information and Assessment Act of 1987 (AB2588 program).  The act establishes a formal air toxics emission inventory risk quantification program, which is managed by California air districts.  The goals of the Air Toxics “Hot Spots” Act are to collect emission data, identify facilities having localized impacts, ascertain health risks, notify nearby residents of significant risks, and reduce those significant risks to acceptable levels.

What does the Act require?

  • Facilities to report of types and quantities of certain toxic substances routinely or predictably emitted;
  • Air districts to determine whether or not a health risk assessment (HRA) must be conducted for the facility;
  • HRAs be conducted according to methods developed by the Office of Environmental Health Hazard Assessment (OEHHA);
  • Public be notified of significant risks posed by nearby facilities, and;
  • Facilities posing significant risks to prepare and implement risk reduction audits within 6 months of the determination.

What is the Air Toxics "Hot Spots" Process?

The California Air Resources Board (CARB) compiles and maintains a list of substances posing chronic or acute health threats when present in the air. The Act identifies by reference over 600 substances, which are subject to the program.

A facility is subject to the Act if it:

  1. Manufactures, formulates, uses, or releases a substance subject to the Act (or another 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, or;
  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.

Emission Inventory Plans and Reports:

  • Facilities meeting the applicability criteria must prepare air toxics emission inventory plans and emission inventory reports. CARB's Emission Inventory Criteria and Guidelines provide assistance in preparing these documents.
  • Facilities must submit a proposed emission inventory plan to MBARD detailing how emissions will be measured or calculated, which MBARD must approve, modify, or return the inventory plan to the operator for revisions within 120 days.
  • Once MBARD approves a plan, the facility operator must implement the plan and submit the emission inventory within 180 days.
  • Facilities subject to the program must update their emission inventories every four years

Risk Assessment:

  • After reviewing emission inventory data, MBARD must rank facilities for purposes of risk assessment into high, intermediate, and low priority categories.  Facilities will be re-prioritized if their inventory update shows any significant changes.
  • MBARD priority categories consider potency, toxicity, quantity, and volume of hazardous materials released, and a facility's proximity to potential receptors.  Additional information on prioritization along with guideline documentation can be found at
  • Within 150 days of designation, high priority facilities and other facilities identified by the District must prepare and submit a health risk assessment (HRA) to the District.  The HRA includes a comprehensive analysis of the dispersion of hazardous substances, the potential for human exposure, and a quantitative assessment of both individual and population wide health risks. OEHHA's Air Toxics Hot Spots Program Guidance Manual for Preparation of Health Risk Assessments supersedes previously published risk assessment methods.

Public Notification:

  • Once the HRA is reviewed by OEHHA and approved by MBARD, the facility must notify all exposed persons of the risk assessment results if MBARD determines that there is a potentially significant health risk (cancer greater than 10 in a million significant risk threshold and non-cancer - hazard index (HI) or total HI greater than 1) or case-by-case consultation with OEHHA recommended.
  • ARB provides general and specific data on toxics at  ARB also provides facility inventory data at

Risk Reduction:

  • Facilities determined to have a significant risk must conduct an airborne toxic risk reduction audit and develop a plan to implement risk reduction measures.  These facilities must submit the audit and plan to the MBARD within 6 months of the determination.  The documents must describe the risk reduction methods the facility will use to reduce its risk below the level of significance within 5 years.  MBARD may shorten or lengthen the time period under certain conditions. 
  • The Act prescribes penalties for failure to comply or for knowingly submitting false information.  Civil penalties range from $500 to $25,000 for each day in violation.  The Act also penalizes for facilities for failure to submit a complete audit and plan or failure to implement the measures set forth in the plan.

What are the Fees?

CARB adopted a fee regulation, which recovers the state's implementation costs. Further information on the regulation and its annual status reports can be found at

The regulation establishes each district's share of state costs and provided MBARD the authority to adopt Rule 305, AB2588 Implementation Fees  to recover the program's costs. MBARD must collect fees from all facilities subject to the Act and remit the district's share of the state costs to the CARB.

Fee categories are based on prioritization scores and health risk assessment results. Fees are based on toxic emissions and facility risk priority to the extent possible and generally increase with increasing risks. Sources not remitting fees to MBARD within 60 days of receipt of the fee notice are subject to additional late fees. Further detail is found in Rule 305.

Guideline Documents

Guidelines for Preparing Air Toxics Emission Inventory Plans and ReportsGuidelines for Calculating Toxic Air Contaminants (TACs) Emissions

MBARD Annual Toxics Report

Annual Toxics Report - 2023Annual Toxics Report - 2022Annual Toxics Report - September 2021Annual Toxics Report - September 2020Annual Toxics Report - August 2019Annual Toxics Report - December 2017

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