ASPEN — Before the COVID-19 pandemic prompted stay-at-home orders and caused an abrupt decline in flights, a busy weekend in March would have meant a long line of jets on the taxiway at the Aspen/Pitkin County Airport.

In a normal year, about one in four of the planes taking off from the Aspen airport is a CRJ-700, the passenger jet used by commercial airlines, which officials say could be phased out by 2028 as airlines transition to newer models that are too large for the current runway. 

On March 10, a county-appointed citizens group called the ASE Vision Committee, which has spent over a year reviewing options for the expansion project, voted 20-to-1 in favor of an integrated package of recommendations for Pitkin County that included widening the runway by 50 feet to accommodate aircraft with longer wingspans and building a new, larger terminal, but only if steps were taken to reduce emissions and noise.

“Environmental responsibility is a cornerstone of our community and should also be a cornerstone of our airport,” the committee wrote.

The committee’s recommendations include suggestions about how to mitigate environmental impacts such as those disclosed by an environmental assessment, or EA, completed in 2018. 

The federally-required EA analyzed the potential actions that Pitkin County had conceptually approved for the county airport and identifies current and potential pollution and carbon emissions. The airport committee members saw the document as a worst-case scenario, according to John Bennet, the chair of the committee, since it did not consider the effects of their proposed mitigation measures.

The EA found that the expanded runway could be expected to increase commercial flights from 8,950 in 2015 to 11,808 in 2033, while private flights are projected to slightly decrease from 30,001 in 2015 to 29,335 in 2033, in line with national trends in general aviation.

Through the long process that led up to the committee’s recent recommendation, locals have expressed concerns about toxic smells, roaring engines and carbon emissions. According to the 2018 EA, expansion of the runway would bring about 2,000 more flights of larger planes and an increase in overall carbon emissions. It would also change the mix of air pollutants coming off the end of the runway, but it’s unclear how that might affect the smells that residents report on busy days.

In terms of noise, some of the planes landing and taking off would be quieter, but there would also be more flights, according to the EA. The sound of idling jets at the North 40 neighborhood, across from the airport, could be mitigated by a large sound wall.

Committee members heard from experts about the air pollution, carbon emissions and noise but decided that the threat of losing commercial service into Aspen outweighed the potential environmental impacts that would remain if the committee’s recommended mitigation efforts were put in place.

“We encourage the county to fully explore federal, state and local policies to incentivize and accommodate aviation innovation in clean emissions and work with partners to stay on the leading edge of environmental sustainability,” the committee said.

They set a goal to reduce pollution and emissions by 30% “as soon as possible, but no later than 2030.” But the committee did not determine a baseline of emissions to measure that goal against, and the county may not be able to control whether all of the committee’s recommendations are implemented.

The recommendations include offering a biofuel blend to decrease greenhouse-gas emissions from the 5.4 million gallons of jet fuel now dispensed each year at the airport, and incentivizing carriers and owners to fly quieter, cleaner models.

The committee also recommends that the county establish a pollutions baseline, and it acknowledges that reducing emissions will depend on negotiations with airlines and the voluntary cooperation of private-aircraft owners, which account for three-quarters of airport traffic.

Skiers ride the Summit Express lift at Buttermilk Ski Resort while jets at Aspen-Pitkin County Airport prepare for takeoff. Some residents are concerned about strong smells from airplane exhaust. Credit: Olivia Emmer/Aspen Journalism

Air pollution and toxic smells remain mysteries

Airplanes departing from the Aspen airport roll down the taxiway, heading upvalley, and then do an about-face to line up for takeoff heading down valley and up and over Woody Creek. Once air control gives the go-ahead, pilots lay on the throttle and jet exhaust erupts from the engines, pointed right at the base of Buttermilk, where kids are learning to ski about a half-mile away on Panda Peak.

“It’s toxic — a thick smell in the air like something’s partially burned,” said Tim Mooney, an Aspen resident who served on subcommittees during the county’s process and is opposed to the proposed runway expansion. “There’s a sudden thrust when they rev the engine up, and you get these blasts of bad air.”

Mooney doesn’t know what he’s breathing downwind from the airport on a busy day, and neither do county officials, as no ground-level air quality measurements have ever been taken at or around the airport. 

The 874-page EA, based on a Federal Aviation Administration modeling tool, uses a potential future fleet mix to extrapolate impacts to air pollution, carbon emissions, noise and traffic from 2015 to 2033.

That is not uncommon, said Mary Vigilante, president of Synergy Consultants, which produced the emissions report in the EA. Ground-level measurements are significantly more expensive than modeling, she said, and “based on these results, there was nothing to indicate warranting doing more detailed work.”

But locals still complain today of a stinging in their eyes and the burned, metallic taste of jet fuel at the Airport Business Center and on the Nordic ski tracks laid each winter on the City of Aspen golf course. 

“My guess is that people are making reference to exhaust associated with volatile organic compounds,” Vigilante said, noting that it could also be nitrogen oxides, or NOx, a family of poisonous, highly reactive gases that form when fuel is burned at high temperatures and help create smog.

The research on the odors is hazy, and there’s no way to know for sure without taking an air sample.

The pollution data in the EA is measured in tons per year, and the specific fumes a person breathes at any moment are jumbled in the average. Plus, the odors vary and are more noticeable on busy days at the airport. There is nearly four times as much activity at the Aspen airport on a busy day in March than on a quiet day in May.

The EA found that if the runway expansion is approved, by 2033 the air pollutant sulfur oxides, or SOx, would increase 1 ton annually  — from 6.9 tons to 7.9 (14.5%) — and nitrogen oxides would increase by approximately 7.4 tons annually — from 42.8 to 50.2 (17.3%).

These changes are nominal and well within federal standards, Vigilante said.

They are also probably overestimated, because the FAA’s model is based on a Boeing 737-heavy fleet mix, and no airline has officially expressed interest in operating the 737 out of Aspen. The plane favored to replace the CRJ-700 is the Airbus 220-100. It is quieter, more fuel efficient and generally cleaner than the CRJ but produces slightly more NOx.

The EA also found that with newer jets, yearly emissions of carbon monoxide, volatile organic compounds and particulate matter would drop slightly, but it is not known whether that is enough to eliminate the taste and smell of burned jet fuel in the community.

The committee’s package of recommendations depends on the airport being able to negotiate with the airlines to operate a clean fleet, and the new class of aircraft that would replace the CRJ-700 on routes into Aspen are generally quieter and more fuel efficient than older models. 

There’s no way to know for sure how private-jet operations will change with the expansion, but the committee’s recommendations rely on jet owners transitioning to newer, greener planes through mechanisms such as a carbon-based landing fee. They also recommend providing electrical hookups for private jets to reduce idling.

“The only reason the proposed expansion is not a slam dunk is that we still have all the private planes,” said John Bennett, chair of the vision committee. “Dealing with them is a totally separate challenge.”

The Clean Air Act forbids the airport from regulating emissions or discriminating over which models can land, so Aspen’s wealthiest residents and visitors will have to do their part willingly.

This does little to assuage the concerns of the opposition group Save Our Skies.

“No one seems to understand the concentration of environmental impacts,” said Wayne Ethridge, a founding member of Save Our Skies and a former Pitkin County commissioner. 

Private jets sit at the Aspen airport. Residents living in the North 40 neighborhood and Woody Creek complain of noise from both private and commercial jets. Newer jets may be quieter, but the airport cannot dictate what planes fly in and out of Aspen. Credit: Brent Gardner-Smith/Aspen Journalism

Noise complaints contrast with data

There are two places where residents are particularly concerned about aircraft noise. Those living and working at the Airport Business Center and the North 40 neighborhood, across Colorado 82 from the airport, hear jets idling and revving up for takeoff. And Woody Creek residents report their windows shaking and conversations stopping as jets roar overhead.

The EA used an FAA model to consider potential changes to noise. It found improving the runway would not increase noise by a standard of 1.5 decibels or more where people live or work, such as the North 40.

The EA also states that there are no homes located within an area that would be exposed to a 65 day-night average sound level, or DNL, the threshold for what the FAA considers to be significant and measured in decibels over a 24-hour period. Woody Creek’s exposure is 51.5 DNL, according to the county’s study.

As with the air pollution data, the noise estimates do not describe a specific moment in time, but a broader study period.

If airlines choose to go with the Airbus 220-100, noise from commercial operators is likely to decrease, as that plane is quieter than the CRJ-700 at takeoff, on the approach and at flyover.

Still, the airport cannot regulate which planes owners or airlines operate, but Bennet said the county can take steps to try to influence their choices.

The committee did recommend that the airport construct a concrete or earthen barrier to protect the ABC and the North 40 from the sound of jets idling and gearing up for takeoff. The EA found that a 14-foot-high wall would lower noise by 5 decibels.

The county now measures noise at Woody Creek year-round and, through its Fly Quiet/Fly Clean Program, encourages pilots to fly considerately over Aspen. 

A study of the program’s data from 2015 to 2017 by a national engineering consulting firm found that, on the whole, private-aircraft operations have gotten quieter. The study scored the private traffic coming out of Aspen a 7.9 on a 10-point scale and noted that the number of extreme-noise events — those above 90 decibels — was 0.1 per day, a reduction over previous years.

“The Fly Quiet program is designed to encourage operators to operate their quietest aircraft at ASE and to fly as quietly as possible,” Ryk Dunkelberg, who worked on the study for the firm Mead and Hunt, wrote in an email.

Still, residents in Woody Creek are concerned that larger jets will not be quieter.

In a letter submitted during the EA process, the Woody Creek Caucus raised concerns that increased traffic and larger, heavier airplanes could “dramatically increase the discomfort of the many residents around the airport and in the flight path. It would be yet another step in Aspen’s path toward commercialization and the loss of Aspen’s unique character.”

An Aspen Skiing Co. employee rakes the features at the Buttermilk Ski Resort while a private jet prepares for takeoff at Aspen/Pitkin County Airport in the background. Approximately 20,000 private jets use the airport annually. The airport vision committee hopes that private-jet owners will voluntarily transition to newer, greener planes. Credit: Olivia Emmer/Aspen Journalism

Carbon emissions will increase with expansion

In the bigger picture, Save Our Skies and many others question whether Aspen should be pursuing, or accommodating, growth at all, given the advancement of climate change. Over the past half-century, the region has lost 12 days with subzero temperatures, and the EA acknowledges that the ski industry in Aspen could be history by 2100.

The City of Aspen’s Climate Action Plan seeks an 80% reduction in greenhouse-gas emissions below 2004 levels by 2050. The airport is not owned or operated by the city but is included in its emissions inventories.

In 2017, the airport contributed 81,566 tons of CO2 — 5% of all GHG emissions in Pitkin County — of which 89% was attributed to aircraft, according to the city’s 2019 GHG inventory report.

The EA estimates that by 2033, the new terminal and widened runway, with the accompanying new fleet makeup and increased operations, would result in an annual increase in GHG emissions of 18%, or 2,515 metric tons.

This projection does not account for recommendations put forward by the committee, including the potential use of solar power, a biofuel blend of jet fuel or a carbon-based landing fee — mitigation measures that don’t go far enough for Save Our Skies.

“The county has declared a climate emergency,” Ethridge said. “At the same time, they seem more than willing to introduce much larger aircraft that will burn more fuel.”

Aspen is not alone in questioning airport expansion. In February, England quashed plans for a new runway at Heathrow Airport in London because it was found to be inconsistent with the country’s climate goals.

The potential ripple effects to the Aspen community and the resort because of the airport’s expansion are even more difficult to quantify, but there will be “growth,” as the number of people flying in and out of the city is expected to increase by about 100,000, from 233,541 to more than 333,000, according to the EA.

Moving forward, county commissioners will consider the committee’s recommendations, which Bennet stressed must be taken as a complete package. The committee submitted a cover letter and its final report to the Pitkin County commissioners this past week, in anticipation of a work session to discuss the recommendations on April 16.

If the county does not accept the recommendations for expansion and the means of addressing the impacts as a package, or if the airlines refuse to negotiate to meet the goals, the committee can reconvene and take another stab at its proposal.

At that point, Bennet said, rather than being in near-unanimous agreement, the committee may split over whether to proceed.

This story was updated on April 11 to add clarity about the relationship between the committee’s recommendations and the EA. Both Wayne Ethridge and John Bennet are donors to Aspen Journalism, each having donated $100 in December. An earlier version of this story was printed in the April 8 edition of The Aspen Times.