How Does CARB Evaluate the Health and Cost Benefits of Reducing Toxic Air Pollutants?

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This fact sheet describes how the California Air Resources Board (CARB) evaluates the health and cost benefits of air toxics regulations and actions taken to reduce air toxics in California.

What Are Air Toxic Pollutant Health Analyses?

Health analyses are used to evaluate the potential public health impacts of toxic substances released into the environment. CARB evaluates the emissions impacts for toxics that are released to the air, including potential cancer and noncancer adverse health effects.

How Are Air Toxics Evaluated?

Air toxics are evaluated by analyzing emissions from the sources and estimating the potential cancer and noncancer health impacts from the substance. The Office of Environmental Health Hazard Assessment (OEHHA) develops health values for toxics like diesel exhaust and hexavalent chromium to determine their level of toxicity and whether they cause cancer or noncancer health impacts. Hexavalent chromium is the second most toxic known substance in terms of cancer risk and is 500 times more potent than diesel exhaust.

How Is Potential Cancer and Noncancer Risk Evaluated?

CARB staff uses the methodology developed by OEHHA^[1] to perform health risk assessments (HRAs) by analyzing emissions from air toxics sources and estimating the potential cancer and noncancer impacts. An HRA is an evaluation, or report, that a risk assessor (e.g., CARB, air district, consultant, community member, or facility operator) develops to describe the potential a person or population may have of developing adverse health effects from exposure to an emissions source. CARB staff conducts HRAs to estimate the cancer and noncancer health impacts of regulations.

Cancer risk is evaluated for multiple pathways of exposure and is expressed as the chance that a given number of people have of developing cancer if one million people were continuously exposed to a toxic air contaminant for a specified period of time.  Noncancer impacts are expressed as a hazard index which indicates the possibility of harmful effects from exposure. Noncancer impacts are expressed as a ratio to the health factors (called reference exposure levels) developed by OEHHA. Long-term noncancer effects may be evaluated from multiple pathways of exposure while shorter exposures (e.g., one hour) are only based on what a person breathes. A multi-pathway analysis can consider a person’s potential exposure from breathing, ingesting soil, food, and water, and absorbing the substance through the skin. Based on these potential exposure pathways, CARB staff can estimate multi-pathway cancer and noncancer risk values for two exposure scenarios: individual residential exposure and off-site worker exposure. Note that CARB does not evaluate risks to on-site workers because risks to on-site workers are regulated by Cal/OSHA.^[2]

How Has CARB Traditionally Evaluated Health Impacts in Past Regulations?

Since 2000, CARB’s regulations have been primarily focused on reducing emissions from diesel PM.  As part of these regulations, CARB staff conducts health analyses that include both a cancer risk assessment and a PM mortality and illness evaluation based on the emission reductions of primary PM2.5 and secondarily-formed PM2.5 from NOx emissions. Exposure to PM2.5 can result in health outcomes including premature death, hospital admissions, and emergency room visits. Based on these analyses, staff estimates the total number of new cases statewide that would be reduced due to the implementation of the proposed regulations. The mortality and illness evaluation discussed above is used for PM2.5 and does not apply to non-diesel air toxics. Currently, there is no methodology to evaluate mortality and illness from non-diesel air toxics.

How Does CARB Currently Assess Diesel PM-Related Health Benefits?

CARB estimates premature death and other health effects related to PM2.5 exposure based on a peer-reviewed methodology developed by the U.S. Environmental Protection Agency.^[3] PM mortality and illness valuation has been, and continues to be, a very important metric for evaluating the health benefits of diesel PM regulations.

In developing regulations such as the Proposed Control Measure for Ocean-Going Vessels at Berth^[4] and the Proposed Amendments to the Commercial Harbor Craft Regulation,^[5] CARB staff monetized the reductions in adverse health outcomes by multiplying the potential new cases by a standard value derived from economic studies.^[6] For example, the value for avoided premature mortality is based on the value of statistical life (VSL), which provides a dollar estimate of benefits for an avoided premature death. The VSL is an estimate of the dollar amount that a large group of people would be willing to pay for a reduction in their risks, such that one death would be avoided in the year across the population. This estimate does not explicitly consider any specific costs associated with mortality such as hospital expenditures.^[7] Ultimately, these Statewide health benefits (in dollar amounts) can be compared to the cost of the proposed regulations.

Why Is It Important for CARB to Develop a Monetization Methodology for Non-diesel Air Toxics Regulations?

CARB staff is proposing amendments to the Airborne Toxic Control Measure for Chromium Electroplating and Chromic Acid Anodizing Operations (Chrome Plating ATCM/Proposed Amendments)^[8] to eliminate potential cancer risk caused by exposure to hexavalent chromium emissions from chrome plating operations. Without a methodology to monetize health benefits from non-diesel air toxics, CARB staff is unable to monetize those benefits from the Proposed Amendments. CARB recognizes the need to develop a methodology that fully monetizes the benefits of reducing cancer and noncancer health impacts from non-diesel air toxics. CARB is working on this effort through a contract, which is looking at developing methodologies to monetize the health benefits from cancer and noncancer risk reductions from non-diesel air toxics. Although these methodologies will take some time to develop and will need to go through a robust scientific peer review process, this will be an important tool to allow us to compare the health benefits to the cost of our regulations.

While non-diesel air toxics regulations do not have PM2.5 emissions reductions and associated benefits, these regulations do have significant emission reductions in air toxics. Over the past thirty years, CARB has adopted many non-diesel air toxics airborne toxic control measures (ATCM). Like the Chrome Plating ATCM, these ATCMs evaluated the baseline potential cancer risk prior to emission control requirements. In the case of the Proposed Amendments for hexavalent chromium, the baseline potential cancer risk, prior to implementation of the Proposed Amendments, is similar to, or on the same order of magnitude as, past non-diesel air toxics and diesel PM-focused ATCMs. Table 1 below shows a brief comparison of baseline potential cancer risks prior to implementation of controls for some previous non-diesel air toxics and diesel PM-focused ATCMs. Table 1 below shows a brief comparison of baseline potential cancer risks prior to implementation of controls for some previous non-diesel air toxics and diesel PM-focused ATCMs.

TABLE 1.  Baseline Potential Cancer Risk from Previous Non-diesel Air Toxics and Diesel PM-focused ATCMs

^a All results have been rounded. The range of maximum individual cancer risk is presented for the baseline scenario (before emission controls for the proposed or amended ATCMs) of each regulation. For ATCMs prior to 2015, the results have been adjusted to reflect current OEHHA risk and exposure methodologies only.

What Resources Are Available?

• For more information on HRAs, visit CARB’s webpage: Health Risk Assessment
• Additional information about the methodology for estimating the health effects of PM2.5 pollution can be found on this webpage: CARB’s Methodology for Estimating the Health Effects of Air Pollution
• To learn more about hexavalent chromium, chrome plating, and chromic acid anodizing operations, please visit CARB’s webpage: Hexavalent Chromium Airborne Toxic Control Measure for Chrome Plating and Chromic Acid Anodizing Operations

^[1] Office of Environmental Health Hazard Assessment, Air Toxics Hot Spots Program, Risk Assessment Guidelines, Guidance Manual for Preparation of Health Risk Assessments, February 2015. https://oehha.ca.gov/media/downloads/crnr/2015guidancemanual.pdf

^[2]Division of Occupational Safety and Health (Cal/OSHA). https://www.dir.ca.gov/dosh

^[3] United States Environmental Protection Agency, Quantitative Health Risk Assessment for Particulate Matter, June 2010. https://www3.epa.gov/ttn/naaqs/standards/pm/data/PM_RA_FINAL_June_2010.pdf

^[4] California Air Resources Board, Public Hearing to Consider the Proposed Control Measure for Ocean-Going Vessels at Berth, Staff Report: Initial Statement of Reasons, October 15, 2019. https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2019/ogvatberth2019/isor.pdf

^[5] California Air Resources Board, Public Hearing to Consider the Proposed Amendments to the Commercial Harbor Craft Regulation, Staff Report: Initial Statement of Reasons, September 21, 2021. https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2021/chc2021/isor.pdf 

^[6]United States Environmental Protection Agency, Appendix B: Mortality Risk Valuation Estimates, Guidelines for Preparing Economic Analyses, December 2010. https://www.epa.gov/sites/default/files/2017-09/documents/ee-0568-22.pdf

^[7] United States Environmental Protection Agency, SAB Report on EPA’s White Paper, Valuing the Benefits of Fatal Cancer Risk Reduction, July 27, 2000.

^[8] California Air Resources Board, Proposed Amendments to the Hexavalent Chromium Airborne Toxic Control Measure for Chrome Plating and Chromic Acid Anodizing Operations, Standardized Regulatory Impact Assessment (SRIA).

^[9]California Air Resources Board, Public Hearing to Consider the Proposed Amendments to the Airborne Toxic Control Measure for In-Use Diesel-Fueled Transport Refrigeration Units (TRU) and TRU Generator Sets, and Facilities Where TRUs Operate, Staff Report: Initial Statement of Reasons, July 27, 2021. https://ww2.arb.ca.gov/sites/default/files/barcu/board/rulemaking/tru2021/isor.pdf

^[10] California Air Resources Board, Public Hearing to Consider the Proposed Control Measure for Ocean-Going Vessels at Berth, Staff Report: Initial Statement of Reasons, October 15, 2019. https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2019/ogvatberth2019/isor.pdf

^[11] California Air Resources Board, Staff Report: Initial Statement of Reasons for the Proposed Amendments to the Control Measure for Perchloroethylene Dry Cleaning Operations and Adoption of Requirements for Manufacturers and Distributors of Perchloroethylene, December 8, 2006.

https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2007/perc07/isor.pdf

^[12] California Air Resources Board, Staff Report: Initial Statement of Reasons for Proposed Rulemaking, Airborne Toxic Control Measure to Reduce Emissions of Hexavalent Chromium and Nickel from Thermal Spraying, October 2004. https://ww2.arb.ca.gov/sites/default/files/barcu/regact/thermspr/isor.pdf

^[13]California Air Resources Board, Staff Report: Initial Statement of Reasons for the Proposed Airborne Toxic Control Measure for Emissions of Chlorinated Toxic Air Contaminants from Automotive Maintenance and Repair Activities, March 10, 2000. https://ww2.arb.ca.gov/sites/default/files/barcu/regact/amr/amr-isor.pdf