California Air Resources Board

The U.S. EPA's 2010 document, Quantitative Health Risk Assessment for Particulate Matter, has noted that reductions in PM2.5 emissions are associated with reductions in the risk of premature deaths, hospitalizations and emergency room visits.  Sensitive groups such as the elderly, and people with chronic heart or lung disease, and children are at particular risk. To estimate these health benefits, staff use CARB’s incidence-per-ton (IPT) methodology. It is based on a methodology developed by the U.S. EPA.123 It is used to estimate benefits of reductions in PM2.5 emitted directly from sources, and PM2.5 formed from precursors by chemical processes in the atmosphere.

The basis of the IPT methodology is that changes in emissions are approximately proportional to changes in health outcomes. IPT factors equal the number of PM-related health effects divided by emissions of PM2.5 or the precursor NOx. The calculation is performed separately for each air basin.

The IPT factor is used to estimate of the reduction in health outcomes achieved by CARB regulations. For future years, the IPT factor is adjusted to account for population growth. CARB’s current IPT factors are based on a 2014-2016 baseline scenario.

CARB's Estimating Health Benefits Associated with Reductions in Diesel PM and NOx Emissions provides a detailed explanation of how health impacts are estimated.

• 1Fann N, Fulcher CM, Hubbell BJ. 2009. The influence of location, source, and emission type in estimates of the human health benefits of reducing a ton of air pollution Air Quality. Atmosphere & Health. 2:169-176.
• 2Fann N, Baker KR, Fulcher CM. 2012. Characterizing the PM2.5-related health benefits of emission reductions for 17 industrial, area and mobile emission sectors across the U.S. Environ Int. 2012 Nov 15;49:141-51.
• 3Fann N, Baker K, Chan E, Eyth A, Macpherson A, Miller E, Snyder J. 2018. Assessing Human Health PM2.5 and Ozone Impacts from U.S. Oil and Natural Gas Sector Emissions in 2025. Environ. Sci. Technol. 52 (15), pp 8095–8103.