How is AQI calculated? Here’s how you can monitor your local air quality in Washington

As fire season lengthens and excessive heat plagues Washington state more frequently during the summer months, checking the air quality goes hand-in-hand with checking the local weather forecast.

External everyday factors such as vehicle fuel emissions, gas from industrial facilities and wildfires affect daily pollution. To measure this, the U.S. Environmental Protection Agency calculates a daily air quality index, known as the AQI, on a scale of zero to 500.

The AQI measures anything from zero to 50 as healthy, while anything at 301 and higher is considered hazardous.

To calculate accurate AQI specifically representative of Washington state’s cities and rural communities, distributed sensor networks are put into place to gather data.

What contributes to poor air quality?

The EPA monitors ground-level ozone pollution, particle pollution, carbon monoxide, sulfur dioxide, lead and nitrogen dioxide. The agency is required to monitor these “criteria pollutants” under the Clean Air Protection Act.

Each criterion pollutant can uniquely contribute to harmful health effects and negative environmental consequences.

According to AirNow, a federal partnership with the EPA, the U.S. National Oceanic and Atmospheric Administration and other government entities, ozone is naturally present in the Earth’s atmosphere. However, pollutants such as ground-level ozone, which are emitted through vehicles, contribute to poor air quality and can “irritate the respiratory system.”

“Good ozone” occurs naturally in the upper atmosphere and protects us from harmful sun rays, according to the EPA. Its counterpart, ground-level ozone, is the toxic pollutant that is “the main ingredient” in smog. Ozone is typically more prevalent in the heat when air is stagnant.

Particle pollution is often a result of wildfires. A study published in the AirNow discovered that “wildfires contribute 15 to 30% of atmospheric primary fine particulate matter emissions in the United States”.

PM2.5, also known as particle pollution, can be spotted in the air. The small floating particles can sometimes create a foggy appearance.

“Emissions of fire pollution is the biggest concern,” said University of California Davis professor Qi Zhang, who teaches in the Department of Environmental Toxicology and conducts research on air pollution.

What is the AQI chart?

The AQI chart is used to classify air quality levels using a formula and the criteria pollutant numbers. A number is calculated daily unless there is an extreme condition, such as a wildfire, which results in it being updated more often.

Zhang said when air quality is stable, the EPA uses 12-hour averages to calculate an AQI.

During fire season, air quality is calculated in real-time. Zhang said ozone levels are calculated hourly, and PM2.5 is calculated every three hours.

The AQI chart is broken into six colors: green, yellow, orange, red, purple and maroon. Each color represents a range on the AQI chart from zero to 500, with zero being “satisfactory air quality” and 500 indicating “health warning and emergency conditions.”

How to protect yourself from bad air quality

One of the most harmful pollutants to humans is ozone. While ozone is great in the upper atmosphere and protects those below from the sun’s harmful ultraviolet rays, in the lower atmosphere it can be poisonous to humans. Ozone is a gas compound made up of three oxygen atoms, which differs from the two oxygen atoms that living things typically inhale as regular air.

Long-term exposure to ozone can damage airways, according to the Environmental Protection Agency, and ultimately is linked to higher rates of mortality.

The first step to staying protected from poor air quality is to keep informed with the most up-to-date AQI in your neighborhood. AQI scores are posted daily on AirNow or can be found on your smartphone’s weather app. If you don’t have access to either, news outlets also inform the public when poor air quality scores are underway.

Cities throughout Washington state like Olympia, Tacoma, Bellingham and the Tri-Cities areas all have air quality monitors to track AQI and inform the community of air quality.

If the air quality in your neighborhood is unsafe, try to avoid going outdoors as much as possible. In your house, shut all your windows and if you have access to an air purifier, use it. Another quick fix would be to switch your air filters in your home.

Staying home is not feasible for everyone, so if you are required to be outdoors during unhealthy air conditions it is strongly advised to wear an N95 mask.

How do you check the AQI?

Here are some resources to compare air quality indexes across the United States: