With all the wildfire smoke in Montana skies this summer, have you been surprised it doesn’t always smell smokey? Or that it smelled like a campfire under clear skies?
It turns out there’s a lot that goes into our perception of smoke and how it squares with the Air Quality Index. And it starts with basic chemistry.
AQI numbers measure solid particles, or particulate matter. PM 2.5 gets a lot of talk during wildfire season because it refers to the size of the smoke particles, which are 2.5 micrometers or less in diameter and it’s particularly harmful to our health.
But what we actually smell isn’t the particular matter. It’s the volatile organic compounds, or VOCs, and they aren’t included in the AQI number. Lixu Jin is an atmospheric chemist at Rutgers University.
“If you go to the bakery store, you will smell very good odor. That's VOC. Depends on which kind of VOCs, it can give you different types of smell. So the VOC from the wildfire smoke, they really depend on the fuel type,” Jin said.
Jin said not all VOCs, like that bakery smell, are bad for our health. But wildfire smoke is the second largest producer of non-cancer causing VOCs, which means they can contribute to diseases like asthma.
Smoke can also change as it ages or travels. For example, before Montana started having its own fires this summer, the state was inundated with smoke from fires in Oregon and Washington. As that smoke travels, it picks up VOCs that can chemically react and produce air pollution. Tracking that is part of the equation, too.
The EPA’s online Fire and Smoke map provides an average every hour using a system called NowCast. But within the map are data from what are called PurpleAir sensors, which update more frequently. So you can toggle between the two to get a more timely and accurate reading of the air quality.
Kerri Mueller is an air quality special with Missoula Public Health. She says this is important because conditions can change quickly.
“If we're seeing smoke roll in, that monitor might not update until the next hour to accurately reflect what the air quality is. And that's where those PurpleAir sensors are helpful to see what the 10 minute-average is, and you can really see those conditions changing faster,” Mueller said.
Both Mueller and Jin emphasize keeping an eye on changing conditions to better protect your health.
“The best thing that you can do if you don't have AC is still opening up your windows when the temperature outside has become cooler than it is inside and bringing in that cool outdoor air and then closing those windows, cleaning your indoor air and maybe doing that once in the evening and then again in the morning,” Mueller said.
