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Pitkin County hears scientific briefing on ultrafine particles; county to continue voluntary airport monitoring
Summary
Consultants told commissioners that ultrafine particles (UFPs) — particles under 0.1 micrometers — are measurable by particle number rather than mass, lack U.S. regulatory standards, and require specialized equipment; the airport’s year‑long voluntary monitoring will report quarterly and inform mitigation planning.
Consultants hired by the Aspen‑Pitkin airport told the Board of County Commissioners on June 9 that ultrafine particles, or UFPs, are airborne particles smaller than 0.1 micrometers that are typically measured by particle number rather than mass. "UFPs are airborne particles that are smaller than 0.1 micrometer or 100 nanometers in diameter," said Jen Wilczynski, the lead consultant for the airport's air‑quality program.
Dr. Roger Reason, the consultant leading technical monitoring, described measurement limitations and options, saying researchers commonly use condensation particle counters for counts and scanning mobility particle sizers to capture size distributions. "When we do that, total number gives us one thing. Are they there? But the size ranges ... gives us much more information because it allows us to now start making estimates, well, where did they come from?" Reason said, noting that size and chemical makeup help distinguish jet exhaust from roadway diesel emissions.
Consultants outlined a voluntary, year‑long measurement exercise that began in April and uses EPA reference monitors on the airfield plus nine additional monitors deployed in the community. The airport will QC the first quarter of data before public release and will provide quarterly presentations to the board and public. "This is voluntary. This is not a requirement," Wilczynski said, describing equipment placement and the plan to pair monitoring with source‑specific emissions modeling.
Speakers emphasized scientific uncertainty and policy limits: there are currently no legally binding U.S. health standards for UFPs, and monitoring methods are not yet standardized, which complicates comparisons across studies. Reason and Wilczynski pointed to international efforts (WHO guidance and EU monitoring programs) and to airport case studies — including LAX, Sea‑Tac and Zurich — that show aircraft can contribute to elevated UFP counts downwind.
Commissioners pressed on study design and cost: whether studies should be treated as research or project monitoring, options for longer‑term deployments and the trade‑offs among equipment cost, mobility and the analytical detail needed to speciate sources. Wilczynski said the airport is developing an emissions reduction action plan and that monitoring results will inform mitigation recommendations such as electrifying ground support equipment and reducing sulfur in fuels.
The board did not take a formal vote but directed staff and the Airport Advisory Board to continue the current air‑quality program and to return with data and potential next steps. Staff said the monitoring results would be presented quarterly and would be used, in coordination with stakeholders, to recommend emission‑reduction strategies for the airport.
