Ultrafine Particle Transport from Arriving Aircraft

Aim: Ultrafine particles (UFP; <100 nm diameter) are highly variable in space and time and as such can be challenging to model for use in epidemiological studies. Recent studies have shown that airports are contributors to local air pollution, but research is needed to understand the impact from individual aircraft and how to incorporate flight activity into UFP exposure models. Our aim was to characterize UFP transport from aircraft exhaust during landing at Boston Logan International Airport (MA, USA). Methods: Particle number concentration (PNC; a proxy for UFP) was measured continuously on selected weeks at the University of Massachusetts Boston campus from April-September 2017 at 1-sec resolution. The site was positioned 4.8 km southwest of the airport edge and <1 km from a major landing trajectory (runways 4L and 4R). Wind speed and direction were concurrently measured near the UFP monitor at 5-min resolution. For this same monitoring period, flight activity data were acquired from the U.S. Federal Aviation Administration, which included three-dimensional positions of aircraft at approximately 5-sec resolution. All data were merged by timestamp prior to analysis. Results: During times when flights were landing on 4L/R, the 99th percentile of 1-sec PNC during winds from the east (no traffic sources) was 88,000 particles/cm3. The concentration dropped >50% when flights were landing along other trajectories during these same winds. Stratification by wind speed showed that when flights were landing along 4L/R, higher wind speeds resulted in increased median PNC during winds downwind of arrival aircraft, but not from the opposite direction. When flights were landing along other runway trajectories nearly all wind directions observed decreased PNC with increased wind speed. Conclusions: Our results suggest that aircraft can play a role in peak ambient UFP exposures during landing and that downwind transport of UFP from aircraft exhaust needs further investigation.