WAC 296-820-860. Appendix B: Calculating the Air Quality Index for PM 2.5 (nonmandatory)

The Air Quality Index (AQI) for PM 2.5 is calculated as follows: Ip = I Hi - I Lo ( C p - BP Lo ) + I Lo BP Hi - BP Lo Ip = I Hi - I Lo ( C p - BP Lo ) + I Lo BP Hi - BP Lo Where: Ip is the Air Quality Index value for PM 2.5 C p is the concentration of PM 2.5 in μg/m 3 truncated to 1 decimal place BP Hi is the concentration breakpoint that is greater than or equal to C p BP Lo is the concentration breakpoint that is less than or equal to C p I Hi is the AQI value corresponding to BP Hi I Lo is the AQI value corresponding to BP Lo Where: Ip is the Air Quality Index value for PM 2.5 C p is the concentration of PM 2.5 in μg/m 3 truncated to 1 decimal place BP Hi is the concentration breakpoint that is greater than or equal to C p BP Lo is the concentration breakpoint that is less than or equal to C p I Hi is the AQI value corresponding to BP Hi I Lo is the AQI value corresponding to BP Lo PM 2.5 BREAKPOINT 1 AQI 1 AQI CATEGORY 1 WA DOH HEALTH MESSAGING 2 0.0-9.0 0-50 Good It is a great day to be active outside and a good time to make a plan if worse air quality is in the forecast. 9.1-35.4 51-100 Moderate Some people are especially sensitive to lower levels of particle pollution and should reduce exposure. For example, limit time outside and avoid strenuous outdoor activity. All sensitive groups should watch for symptoms. 35.5-55.4 101-150 Unhealthy for sensitive groups Sensitive groups should take steps to reduce exposure. Limit time outside, avoid strenuous outdoor activity, and follow tips for cleaner indoor air. Everyone should watch for symptoms as a sign to reduce exposure. 55.5-125.4 151-200 Unhealthy Everyone should reduce exposure. Limit time outside, avoid strenuous outdoor activity, and follow tips for cleaner indoor air. 125.5-225.4 201-300 Very unhealthy Everyone should reduce exposure. Stay inside and filter indoor air to keep it cleaner. Go elsewhere for cleaner air, if needed. 225.5 or more 301 or more Hazardous Everyone should reduce exposure. Stay inside and filter indoor air to keep it cleaner. Go elsewhere for cleaner air, if needed. PM 2.5 BREAKPOINT 1 AQI 1 AQI CATEGORY 1 WA DOH HEALTH MESSAGING 2 0.0-9.0 0-50 Good It is a great day to be active outside and a good time to make a plan if worse air quality is in the forecast. 9.1-35.4 51-100 Moderate Some people are especially sensitive to lower levels of particle pollution and should reduce exposure. For example, limit time outside and avoid strenuous outdoor activity. All sensitive groups should watch for symptoms. 35.5-55.4 101-150 Unhealthy for sensitive groups Sensitive groups should take steps to reduce exposure. Limit time outside, avoid strenuous outdoor activity, and follow tips for cleaner indoor air. Everyone should watch for symptoms as a sign to reduce exposure. 55.5-125.4 151-200 Unhealthy Everyone should reduce exposure. Limit time outside, avoid strenuous outdoor activity, and follow tips for cleaner indoor air. 125.5-225.4 201-300 Very unhealthy Everyone should reduce exposure. Stay inside and filter indoor air to keep it cleaner. Go elsewhere for cleaner air, if needed. 225.5 or more 301 or more Hazardous Everyone should reduce exposure. Stay inside and filter indoor air to keep it cleaner. Go elsewhere for cleaner air, if needed. 1 Federal Register Vol. 89, No. 45, Page 16405, March 6, 2024: http://www.govinfo.gov/content/pkg/FR-2024-03-06/pdf/2024-02637.pdf. 2 Washington Department of Health. April 2022, accessed March 14, 2024. Washington Air Quality Guide for Particle Pollution: https://doh.wa.gov/sites/default/files/legacy/Documents/4300/waqa%20infographic%5fEnglish.pdf?uid=64384c71c8715 .