Recently, my wife and I were out for an evening walk. Knowing that there was the possibility of smoke in the air due to fires in Northern Minnesota and Canada, I checked my smartphone app before heading out. It displayed an Air Quality Index (AQI) of 71. Not great, but considered safe for healthy people.
About a mile from our home, I noticed the air had suddenly become very hazy, with the strong smell of smoke, and everything was starting to take on an orange tone from the evening sun. I was starting to feel some congestion. We turned around and headed back.
I rechecked the AQI on my phone app, and it had not changed. I then checked airnow.gov and the AQI was reported as over 200 in my city. This is a level that is a health risk for everyone. The unexpected smoky air could have had serious consequences even with a short exposure, if we had asthma, COPD, cardiovascular disease, or some other chronic illness.
Wildfire smoke contains many harmful particles and gases. The most worrisome is fine particulate matter (PM2.5). These particles are about 30 times smaller than the diameter of a human hair and can bypass the upper airway defences, depositing deep in bronchioles and alveoli.
In fact, they can cross into the bloodstream and trigger inflammation throughout the body. This, of course, exacerbates asthma and other chronic conditions and can even put healthy people at risk of illness depending on the exposure.
The U.S. Environmental Protection Agency (EPA) AirNow website and mobile app are considered the primary source for official air quality information in the United States. (just look up airnow.gov or get the mobile app).
AirNow compiles data from thousands of regulatory-grade air monitoring stations operated by federal, state, tribal, and local agencies. Air quality is reported using the Air Quality Index (AQI), a standardized scale that converts pollutant concentrations into health risk categories ranging from Good (green) to Hazardous (maroon).
AirNow also incorporates wildfire information from the U.S. Forest Service and NOAA, including active fire locations, smoke plume estimates, and temporary monitoring stations deployed during large wildfire events. The information shows up about 30 minutes after the previous hour.
AirNow may conflict with Apple Weather because they use different data sources. Apple Weather relies on proprietary models and low-cost sensor data via BreezoMeter, and uses computer models for hyperlocal conditions.
During wildfire season, the AirNow Fire and Smoke Map provides more detailed information than the standard AQI map. In addition to regulatory monitors, it incorporates corrected data from thousands of PurpleAir low-cost PM₂.₅ sensors.
PurpleAir is a privately operated network of low-cost particulate matter sensors installed by homeowners, businesses, schools, and government agencies. However, PurpleAir sensors are not regulatory-grade instruments. Their measurements can be affected by humidity, sensor aging, and environmental conditions.
Raw PurpleAir readings may overestimate or underestimate particulate concentrations unless correction factors are applied. For this reason, the EPA incorporates corrected PurpleAir data into the AirNow Fire and Smoke Map rather than relying on the unadjusted sensor values.
This network greatly increases geographic coverage in communities that lack permanent monitoring stations. This hybrid approach allows users to identify localized smoke conditions that may not be detected by the relatively sparse regulatory monitoring network.
There are a few challenges to obtaining real-time AQI numbers. Regulatory air quality monitors are expensive to purchase and maintain, so they are relatively few in number. Large rural areas, mountainous regions, and wilderness communities may be many miles from the nearest monitoring station.
Air quality at a patient’s location may therefore differ a lot from the nearest official monitor, particularly during wildfire events when smoke distribution can change dramatically over short distances.
Wildfire smoke is highly dynamic. Wind shifts, changes in fire intensity, atmospheric inversions, and local terrain can cause particulate concentrations to increase or decrease within minutes. A community with excellent air quality in the morning may experience hazardous conditions by afternoon, while another nearby location improves simultaneously. These rapid fluctuations can outpace scheduled forecast updates and challenge even sophisticated forecasting models.
Many official AQI products are based on averaged measurements rather than instantaneous readings. Data must also undergo quality assurance before publication. As a result, there may be delays between changing environmental conditions and publicly reported AQI values.
Low-cost sensor networks often update more frequently but may sacrifice measurement accuracy. The EPA acknowledges that sensor data may occasionally be delayed, unavailable, or affected by transmission or measurement errors.
Checking AQI on airnow.gov app before heading outside is just as important and maybe more so than just checking the weather. Stay indoors if possible during unhealthy air quality, close windows and doors, and use a HEPA filter.
Wear an N95 mask if outdoor exposure is unavoidable. Surgical masks, cloth masks, and face coverings do not provide adequate protection against wildfire smoke particles. Vulnerable individuals such as children, older adults, pregnant women, and anyone with a chronic medical condition need extra caution.
In wildfire season, it is a good idea to have an N95 mask readily available in case the air quality suddenly changes.
References:
AirNow website https://www.airnow.gov/about-airnow/.
AirNow Wildfire Smoke: A guide for Public Health Officials.
North Carolina State University Air Quality Portal PM2.5 Data Discrepancies Explained- Part 5 of 5 https://airquality.climate.ncsu.edu/2024/04/02/pm2-5-data-discrepancies-explained-part-5-of-5/.
