ASPEN - Aspen has been keeping tabs on the particulate pollution in its air for 25 years. This month, it's fine-tuning the effort as an experiment.
The city's monitor, atop the Pitkin County Library, has been recalibrated to detect much smaller particulate matter than what traditionally has been its focus. Rather than the so-called PM10, the city will measure PM2.5 for the month of March and again in the spring, possibly in May, according to C.J. Oliver, environmental health director.
PM10 stands for particulate matter of 10 microns or less. (A micron is tiny - there are about 25,400 of them in an inch, according to wiki.answers.com.) In Aspen, PM10 is generally the grit brought in on the wind or ground up by tires on city streets that have been sanded after each snowfall, according to Oliver. The city began monitoring it in 1988 and subsequently implemented measures to reduce what was then, at times, problematic particulate pollution.
PM2.5 is even smaller matter, generally associated with combustion - vehicle exhaust and smoke, for example, Oliver said.
"We're curious to see what percentage of our particulate matter is that smaller stuff," he said. "I'll be curious to see. I'd be surprised if we have significant 2.5 issues here."
What the city does about PM2.5, if anything, depends on what it finds out about the levels of PM2.5 in the air, Oliver said.
City officials long ago realized that reducing vehicle trips was necessary in order to lower PM10 levels. Measures taken toward that goal over the years include paid parking, which partly funds free transit service in town, expanded bus service and free parking for car poolers, along with an aggressive street-sweeping regimen once the snow melts each spring.
In addition, the city has outlawed old-style fireplaces and woodstoves that send particulate matter up the chimney (existing ones are allowed to remain) and placed limits on gas fireplaces in new buildings.
Those steps might help reduce PM2.5, as well, Oliver said.
There was no cost to recalibrate the city's monitor to track PM2.5, and no data will be lost, Oliver said, because two state monitors in Aspen continue to track daily PM10 levels.
The ingestion of particulate matter is linked to health risks, particularly for those with respiratory problems. Ultimately, the city could issue alerts when levels of particulate matter in the air are especially high, Oliver said.
And, with the city's monitor due for replacement, the city could opt for a new model that measures both PM10 and PM2.5 if this spring's experiment suggests continual monitoring of PM2.5 is warranted, he said.
Aspen also monitors its ozone levels, an effort that began in 2009.