Pa. measures air quality with colors. Here’s what they mean

• Rachel McDevitt
  BioRecent Stories

  

  I report on energy and the environment for StateImpact Pennsylvania at WITF.
  
  My work focuses on responses and solutions to climate change in the state legislature and communities around the state. I trace my interest in these issues back to my time as a Girl Scout and this episode of Rocko’s Modern Life.
  
  I look forward to winter just for the chance to ski a few times each season. I try to keep myself from doom-scrolling on my phone by keeping my hands busy knitting and learning to play the piano.
  
  I grew up in Cambria County, Pa. and graduated from Temple University. I started at WITF just after Christmas in 2014.

Haze hangs over Harrisburg as smoke from Canadian wildfires filtered into Pennsylvania on June 8, 2023. The smoke degraded air quality across Pennsylvania and other states in the northeast. Jeremy Long - WITF News

Pennsylvania is under a cloud of unhealthy air caused by smoke from Canadian wildfires.

The state Department of Environmental Protection on Wednesday declared a Code Red Air Quality Action Day for the entire state.

But in some places, actual air quality reached more dangerous purple and maroon levels.

The federal Environmental Protection Agency measures and rates air pollution on a scale from 0 to 500 called the Air Quality Index. The lower the number, the cleaner the air.

The AQI is also broken into colors.

Green (0-50) is healthy. Yellow (51-100) is seen as acceptable.

Orange (101-150) means the air is likely to affect certain groups, such as the very young, old, and people with asthma.

An AQI in the red zone (151-200) means even people without sensitivities could feel health effects from breathing the dirty air. The EPA recommends people limit outdoor activity.

Purple (201-300) is very unhealthy and maroon (301-500) is hazardous. When the AQI is above 300, it ranks as a health emergency and all people in the area should avoid spending time outside.

DEP’s air quality action alerts are based on forecasts and are generally not updated frequently in a day, which is why actual air quality can be more severe than what is warned in the alert. Usually the alerts are for specific geographic locations because of weather patterns and nearby industry.

DEP spokesman Neil Shader said the pollution caused by Canadian wildfire smoke is uncharted territory for the agency.

During periods of high pollution, people can check area-specific AQIs, updated hourly, at airnow.gov.

The website shows two AQI scores; one for particle pollution and one for ozone. Particle pollution is made up of very small pieces of soot, metals or other toxics that can get embedded in the lungs. Ozone is a gas that’s harmful when breathed in. It forms from a combination of heat and different pollutants known as volatile organic compounds.

EPA is forecasting an AQI in the orange range for Friday. DEP says smoke is expected to hang around into the weekend, though it won’t be as dense as Wednesday and Thursday.

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About StateImpact Pennsylvania

StateImpact Pennsylvania is a collaboration among WITF, WHYY, and the Allegheny Front. Reporters Reid Frazier, Rachel McDevitt and Susan Phillips cover the commonwealth’s energy economy. Read their reports on this site, and hear them on public radio stations across Pennsylvania.

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