=

IHi - ILo

(Cp - BPLo) + ILo

 

 

BPHi - BPLo

 

Where:

 

is the Air Quality Index value for PM2.5

is the concentration of PM2.5 in μg/m3 truncated to 1 decimal place

is the concentration breakpoint that is greater than or equal to Cp

is the concentration breakpoint that is less than or equal to Cp

is the AQI value corresponding to BPHi

is the AQI value corresponding to BPLo

PM2.5 THRESHOLDS1

AQI1

AQI CATEGORY1

WA DOH HEALTH MESSAGING2

0.0-12.0

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.

12.1-35.4

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.

55.5-150.4

151-200

Unhealthy

Everyone should reduce exposure. Limit time outside, avoid strenuous outdoor activity, and follow tips for cleaner indoor air.

150.5-250.4

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.

250.5-350.4

301-400

Hazardous

Everyone should reduce exposure. Stay inside and filter indoor air to keep it cleaner. Go elsewhere for cleaner air, if needed.

350.5-500.4

401-500

Hazardous

Everyone should reduce exposure. Stay inside and filter indoor air to keep it cleaner. Go elsewhere for cleaner air, if needed.

˃ 500.4

Beyond the AQI

Hazardous (beyond the AQI)