Montana State weather instruments monitor air quality

BOZEMAN - As wildfire smoke continues to collect heavily across parts of Montana, Joseph Shaw logs into his computer to check the data gathered from a weather station atop Montana State University's Norm Asbjornson Hall. What he saw a few nights ago was a first in his 20 years of collecting weather-related data.

"I would say on a normal, clear day in Montana the scattering coefficient would be five, or maybe 10," said Shaw, who is a distinguished professor of electrical and computer engineering in MSU's Norm Asbjornson College of Engineering. "Around midnight a few days ago, it was 516, which is the highest that I've ever measured."

The scattering coefficient measures how strongly airborne particulate matter redirects light as it passes through a given distance in air. The corresponding air quality index value of 232 triggers a "very unhealthy" warning from the U.S. Environmental Protection Agency, advising sensitive groups to avoid all outdoor exertion, and for everyone else to limit outdoor exertion.

The weather station at MSU has the instrumentation to measure and report a bevy of scientific weather data, including the air quality index. He installed the instruments piecemeal over two decades to provide more accurate location-specific data for researchers around the world to utilize. One of the differences between the campus-centric data generated by the weather station at MSU and Bozeman-area weather data often available through smartphone apps is that the latter often comes from a weather station located at Bozeman-Yellowstone International Airport. Despite being less than nine miles from campus, the airport can experience weather conditions that are measurably different from those of MSU's campus, Shaw said.

Another difference is that Shaw's data isn't available via an app. The data are intended mostly for scientific research, so the web-based interface might appear non-intuitive to laypersons. But to see a real-time user-friendly measurement of the current AQI at Asbjornson Hall, visit the PurpleAir website, which is part of the global AERONET network of weather-data gathering stations. The campus-specific data updates from Shaw's instruments every 10 minutes, 24 hours per day.

"Our instruments suck air in and they scatter laser light off of it," he said. "They then determine how many particles are there from that laser light."

Of particular interest, Shaw said, are the smallest particles with diameters less than 2.5 micrometers, which can enter people's lungs and cause irritation and sometimes exacerbate medical conditions such as asthma, he said. The larger particles tend to migrate to the ground relatively quickly, he said. The density of the smallest particles is used in the EPA-defined calculation for the AQI.

Despite having access to a cluster of comprehensive weather-related instruments, Shaw sometimes uses another measurement for air quality - at least when smoke in the air isn't making headlines. He uses the line-of-sight clarity of mountains 30 to 40 miles away as a means of approximating visually the amount of haze in the air.

"For light haze, I use the visibility of the Tobacco Root Mountains from the top of Asbjornson Hall," said Shaw, who is also director of MSU's Optical Technology Center.

OpTeC is a globally recognized center advancing optical technology through research, education and collaborations with private industry.