Air-quality studies conducted in June and September and that came out of discussions concerning the pending redevelopment of the Aspen-Pitkin County Airport returned scant evidence of hazardous air pollutants in levels high enough to harm human health.

However, studies conducted by two contractors hired by Pitkin County last spring turned up trace amounts of pollutants. But one of the reports, conducted by Air Resource Specialists (ARS) of Fort Collins, questions whether the pollutants are related to airfield operations, and notes that car traffic on Highway 82 is “likely the dominant local source of emissions near the monitoring station.”

County officials, as well as representatives of the hired companies and others involved in the studies, will be on hand for a work session Tuesday at 1 p.m. with Pitkin County commissioners to discuss the study results and determine whether more air-quality analysis is needed.

The sensors for the studies were placed on the roof of the North 40 fire station, located east of the airfield across the highway. The site was selected, in part, because county officials wanted a secure space for the sensors where they would not be stumbled upon or tampered with, but the choice was also in response to concerns raised by residents of the North 40 subdivision.

“Residents in the neighborhoods located adjacent to (the airport) have complained about odors believed to be associated with airport operations and the presence of odors have also generated concerns about potential health effects associated with airport-related emissions,” the report says. Since the fire station is closer to the airfield than the North 40 neighborhood, the consultants assumed that the site would experience greater air-quality impacts than the neighborhood itself.

A committee that met for over a year and was charged with hammering out a concept for redeveloping the airport so it can accommodate planes with larger wingspans — and while adhering to community values — set a goal of reducing pollution and emissions by 30% from existing operations. However, at the time ASE Vision Committee’s recommendations were finalized in March, the county had not conducted on-the-ground air-quality monitoring, although an environmental assessment concerning the potential redevelopment in 2018 estimated pollutants based on modeling. The two studies that will be discussed at Tuesday’s commissioners meeting were part of the effort to build that baseline data.

Air quality monitoring equipment on the roof of the North 40 fire station in June 2020. Pitkin County commissioned two air quality studies, bot of which took samples in June and September, to help develop the understanding of baseline conditions associated with the Aspen/Pitkin County Airport. Credit: Image courtesy of Air Resource Specialists

Pollutants found, but at low levels

The ARS sensors, which collect data in 24-hour intervals, were deployed on the roof of the fire station between June 9 and June 14 and between Sept. 15 and 20. The sensors and sampling methods used meet Environmental Protection Agency standards for detecting volatile organic compounds (VOCs) and can analyze for 60 different compounds.

During the September monitoring period, the smoke waves from the Grizzly Creek Fire in Glenwood Canyon were impacting air quality in the Aspen area, which may have impacted results.

The sensors detected seven VOCs on at least one day in June and 18 on at least one day in September. Three compounds — chloromethane, dichlorofluoromethane and ethanol — were found in all samples in each monitoring period. Acetone was detected in three of six samples during the June study and in five of six samples during the September study.

The ARS report notes that both chloromethane and dichlorofluoromethane are “classified as chlorofluorocarbons (CFCs), which were commonly used in the past as refrigerants and as propellants for consumer products such as aerosol spray cans. Use of these compounds has been discontinued in the United States and other parts of the developed world. However, CFCs are very stable and are unlikely to degrade in the atmosphere, so their presence in the (Aspen samples) likely comes from residual concentrations caused by historical emissions of these compounds and/or global transport of emissions from areas of the world where use of these chemicals continues.”

The presence of ethanol, a constituent of gasoline, in the samples could be related to the nearby gas station, the report says.

Acetone is a solvent that may be used for cleaning of plastic, metal and composite products, the report says. Acetone may also be present as a constituent of wildfire smoke.

“The Aspen area was being impacted by wildfire smoke during the (September) monitoring period, which could explain why higher acetone concentrations were measured during (that phase),” the report says.

Benzene was also detected on two of the six days in the September monitoring period.

In all cases, the concentration of pollutants detected was far below “reference concentrations” established by the EPA as a threshold beyond which human health is believed to be threatened. Although not all the pollutants identified have established corresponding reference concentrations, the cases where one exists tell a similar story.

For example, the highest reading for chloromethane — 2.2 micrograms per cubic meter, on Sept. 15 — was well below the EPA reference concentration of 90 micrograms per cubic meter. The highest benzene reading of 1.6 micrograms per cubic meter was a fraction of the reference concentration of 30 micrograms per cubic meter.

There is no established reference concentration for acetone, but according to the report, the EPA’s “Integrated Risk Information System” suggests that concentrations need to exceed 100 parts per million.

“Measured concentrations of acetone in the (Aspen samples) were substantially under these levels,” the report says.

The September monitoring dates were selected because the airport was closed for three of the six days for a maintenance project.

“It was postulated that any significant differences in the measured air quality concentrations between days with and without (Aspen airport) operations would be theoretically attributable to aircraft emissions or otherwise associated with (airport) operations,” the report says. “However, the results did not show any significant increase in concentrations for any of the measured pollutants. As such, it does not appear that airfield emissions significantly impact VOC concentrations in the immediate area.”

Also, there was little difference in the number of takeoffs and landings at the airport during the days studied in 2020 compared with 2019, despite reductions in commercial air service resulting from the COVID-19 pandemic. More than three quarters of ASE traffic is attributable to general aviation, as opposed to commercial flights.

The ARS study concludes that “adverse health effects in the vicinity of (the Aspen airport) did not occur during the sampling events, whether from aircraft emissions or other emission sources.”

The authors don’t doubt the presence of odors that have been the subject of neighborhood concern and attributed to airfield emissions. “However, odors are typically transient and usually of short duration,” the report says. “Odors may be present, but the associated concentration can occur at levels that do not cause adverse health impacts.”

This table shows concentrations of VOCs found during a September monitoring period during a two-phase study conducted by Air Resource Specialists of Fort Collins. Credit: Air Resource Specialists

Additional data finds no exceedance

The county also contracted with APIS, an Oregon-based company, to conduct additional air-quality monitoring using sensor technology that is more cost effective and simple to operate, but it is not sanctioned by the EPA as a reliable regulatory method.

“The accuracy of the data may vary from sensor to sensor,” says a report by Andrea Holland, who analyzed the APIS data for the county. She noted that the sensors used to collect the APIS data are known to overestimate pollutant concentrations. “However, they do provide information about local air quality that helps determine areas where air quality may be a concern and requires more robust and accurate monitoring.”

The APIS sensors were also on the roof of the North 40 fire station and collected data for nitrogen dioxide and particulate matter. They collected data from June 5-29 and from Sept. 1-28, although the particulate matter sensors in September were operational Sept. 22-28.

The “national ambient air-quality control standard” for nitrogen dioxide exposure in a one-hour period is 100 parts per billion, meaning that exposure below those levels is not believed to be harmful. The highest one-hour reading observed in the APIS study was 65 parts per billion, on June 20. Most readings were between 15 and 25 parts per billion.

Readings of particulate matter were also below air-quality control standards.

“No exceedance of (national ambient air-quality control standards) was detected for any of these pollutants,” Holland’s report says.

This map shows the location of the North 40 fire station in relation to the Aspen/Pitkin County Airport. Credit: Air Resource Specialists

A snapshot, not the final word

Pitkin County Community Development Director Cindy Houben characterized the two air-quality studies as a “snapshot.”

“We definitely need to dig deeper,” she said, as plans move forward for the airport project that will include a new terminal and a reconfigured airfield that can accommodate planes with longer wingspans.

Staff’s recommendations include conducting more air-quality research focused on the upvalley end of the runway, which bears the brunt of emissions when planes take off.

“Specifically, a winter study may show different (air-quality) parameters given inversions where air is trapped closer to the ground before dispersing,” says a memo to the commissioners in advance of Tuesday’s meeting.

Staff further recommends an ongoing air-quality program that makes regular calculations of emissions.

Houben said the county remains concerned about the odor around the airport, recognizing that it can be “overwhelming” at times.

She also said there should be more analysis of the impacts of the hazardous pollutants, regardless of whether or not the concentrations are found to be below federal standards.

“People are going to say the feds are the feds … and we should do better,” Houben said.

This story ran in the Jan. 19 edition of The Aspen Times.


Curtis Wackerle is the editor and executive director of Aspen Journalism and the editor and reporter on the Connie Harvey Environment Desk. Curtis has also served as editor, managing editor, and reporter...