Anyone who’s suffered a sunburn has likely heard of the UV Index. The rating system tells us when and for how long it’s safe to be in the sun, and is a key tool in helping the general population avoid skin cancer. Perhaps less commonly known is the Air Quality Index (AQI, for short), a system designed to alert us when to dangers we might not be able to see.
Every day, the government provides a snapshot of the air we breathe as we go about our lives—working, playing with our kids, or simply resting next to an open window. Here’s everything you need to know about the AQI and how it protects our health:
What’s Air Quality Index and where did it come from?
The Air Quality Index is a 0-500 scale used by the Environmental Protection Agency (EPA) to report and forecast air pollution. In 1976, the EPA created the Pollution Standards Index in order to create a nationally uniform reporting system for tracking healthy air levels. In 1999, it was renamed the Air Quality Index and revised to reflect the system we use today.
What are the criteria for our AQI?
The U.S. focuses on the concentrations of the five major pollutants monitored by the Federal Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. The highest measurement of any single pollutant dictates that day’s AQI value, all of which are reported on the color-coded AirNow monitoring system.
What do the colors mean?
AQI is segmented on a 0-500 scale based on pollution and health effects. To level-set: A rating of 100 correlates to the public-health standard of a given pollutant.
Here’s how the scale breaks down:
Does the AQI reach ‘unhealthy’ levels in the U.S.? What happens when it does?
The AQI often reaches the unhealthy “red” level in some parts of the U.S. and, rarely, “very unhealthy” and “hazardous” in areas of Idaho and Alaska. This January, the Pacific Northwest, Idaho, and Montana have all had red-AQI alerts. On those days, officials urge people to stay indoors, filter the air in their homes, and drink a lot of water, which allows the body to better dilute phlegm and dislodge smoke particles.
What could be causing air quality to dip on those areas?
AQI measurements can fluctuate based on season, weather patterns, and climate events. In the winter, for instance, carbon monoxide levels are often high because cold weather can stymie some vehicles’ emission-control systems. Additionally, thermal inversions (when layers of warm air settle above cooler air near the ground) are more frequent in the winter; this phenomenon traps emissions from vehicles and wood-burning and leads to drastic deterioration of air quality. In the summer, sunlight and heat can cause volatile organic compounds and nitrogen oxides to form ozone more rapidly.
Do any U.S. cities have poor air quality year-round?
The five worst offenders for year-round particle pollution and also ozone pollution are all in California, according to the American Lung Association. They include: Los-Angeles-Long Beach, Madera-Fresno, Visalia-Porterville-Hanford, Bakersfield, Modesto-Merced, and Sacramento-Roseville.