Where There’s Smoke, There’s AQI

On June 7, 2023, Yahoo News reported that "the EPA's AIRNow app sat at number 13 most downloaded free apps on the App Store for iPhone. This made it more popular than Netflix, Cash App, Snapchat, Telegram, and Facebook." Wildfire smoke was blanketing heavily populated areas of the northeastern U.S., presumably leading people to care more about Air Quality Index (AQI) than about entertainment or keeping up with their friends. What is AQI, and what does it tell us? 

The Air Quality Index (AQI) is an air pollution standard used by governments for the public communication of current and forecast air quality conditions. In the U.S., the Environmental Protection Agency (EPA) sets the protocol for determining the AQI and for collecting and disseminating AQI data.

Six atmospheric pollutants are used to determine air quality:

• Ground-level ozone (O₃)

• Fine particulates (PM 2.5 = diameter 2.5 μm* or less)

• Coarse particulates (PM 10 = diameter 10 μm* or less)

• Carbon monoxide (CO)

• Nitrogen dioxide (NO₂)

• Sulfur dioxide (SO₂)

(* 1 micron, abbreviated μm, equals 1/1000 mm)

The concentration of each pollutant is measured over the course of 24 hours and an AQI is calculated for each pollutant individually. The highest AQI of the six is the reported AQI for that monitoring station. When the EPA reports the AQI, the pollutant responsible for the AQI index will be shown on the AQI dashboard. For example, in the figure below, in Ithaca NY, 9:00 AM June 7, 2023, the AQI was 351, determined by the PM 2.5 concentration.

The EPA has assigned a color-coded hazard level to each of six divisions for AQIs below 500:

0-50              Good

51-100         Moderate

101-150      Unhealthy for sensitive groups

151-200      Unhealthy

201-300      Very unhealthy

301-500      Hazardous

An AQI above 500 is considered "out of range," and extremely hazardous.

There are probably many of us who looked at the AQI for the first time during the first week of June, 2023, when smoke from Canadian wildfires drifted south, blanketing cites in the eastern U.S. During extreme events like this one, the AQI is updated more frequently than usual. Notice, in the definition above, that pollutants are monitored for 24 hours in order to determine the AQI. This means that, under normal conditions, the reported AQI tells us what was happening yesterday. That is less useful when the atmosphere is dynamic or the concentrations of pollutants are highly variable. In dynamic circumstances the AQI can be updated every 12, 8, or 3 hours, or even every hour. For this reason, the EPA has developed its NowCast, which is a model that assesses the variability of air quality and changes the observation period accordingly. You can see more of the EPA’s air quality maps and tools at AirNow.gov.

At the Cayuga Nature Center, the PRI Climate Team monitors local air quality year-round. Every five minutes, we record the air temperature, atmospheric pressure, relative humidity, and the concentration of CO2, PM1, PM2.5, PM10, and volatile organic compounds. Our system calculates the Heat Index and AQI every 12 hours, and indicates which pollutant is responsible for the AQI.

The particulate matter measured at any one time by the Nature Center’s sensor could consist of a variety of tiny solid and liquid materials: acids, organic compounds, and metals from industrial activity, soil and dust, allergens like bits of pollen or mold spores, and wildfire smoke. The sensor is designed to measure particles with diameters less than 10 μm because those are the ones that can enter our lungs and stay deep within them, and even enter our bloodstream. Once in our bodies, these particles are especially dangerous for children and elderly adults, people with chronic respiratory diseases like asthma and COPD, and people with heart disease.

On days when the air quality around you is bad, you can protect your lungs and heart by limiting your time outdoors as much as possible. You can also avoid strenuous exercise that makes you pull more particles into your lungs. If you must spend time outdoors, N95 and KN95 masks are the best readily available choice. The U.S. government has fact sheets about protecting people and animals from wildfire smoke. Wild animals, sadly, can suffer terribly in smoke and fire, without means to protect themselves.

People in parts of the U.S. with high levels of pollution are used to checking the local air quality before going out in the morning, just like they might think to put on sunscreen. Here in the northeastern U.S., we have our share of poor air quality from industrial and transportation pollution. We are not, however, used to poor air quality from wildfire smoke; we tend to think of wildfire smoke as coming from the western part of North America, as it did in 2021 (see blog post “Wildfire Season Off With a Bang”). Now, in early June of 2023, smoke is being blown south to us from wildfires in Quebec, Canada as well as from the west. And it is ranging far beyond us.

The smoke in our air from nearby Canada invites asking if wildfires are expected to become more common here in Upstate New York as the climate changes. In the remainder of this century, the northeastern U.S. is projected to experience more extremely hot days and more short-term drought. These changes can lead to conditions that make wildfires more likely.  A study published in 2016 [2] concluded that fire risk in the Northeast and Great Lakes region will increase during the 21st century in the summer—though it’s a moderate increase. The biggest changes are projected to be that wildfire season will start and peak earlier in the year, and times of high risk are going to increase in length.

In addition, the northeastern U.S. has large areas of forest land that came back after a period of deforestation in the 18th and 19th centuries. Indigenous peoples used to manage the land with prescribed burns, but we did not use these practices on a large scale as our forests regrew in the 20th century, leaving a lot of forests with potential to burn.

Air quality, human health, and climate change are intimately connected. For example, cars that burn gasoline produce pollution that leads to ground-level ozone, which irritates our lungs, as well as carbon dioxide pollution that heats the planet. Higher temperatures make ozone pollution worse and increase wildfire risk, amplifying threats to our health. While we need to practice forest management to prevent wildfire disasters and to take steps to protect our health during smoke events, it is imperative that we take rapid action to stop heating our planet. If we do this, future threats will be less extreme and less costly, both financially and to our health and quality of life. 

References

[1] Kyle Barr, EPA’s Air Quality App Is More Popular Than Facebook Right Now, Yahoo! News, June 7, 2023. https://www.yahoo.com/lifestyle/epa-air-quality-app-more-194843192.html, accessed on June 12, 2023.

[2] Kerr, G. H., DeGaetano, A. T., Stoof, C. R. & Ward, D. Climate change effects on wildland fire risk in the Northeastern and Great Lakes states predicted by a downscaled multi-model ensemble. Theoretical and Applied Climatology 131, 625–639 (2018). DOI: https://link.springer.com/article/10.1007/s00704-016-1994-4