Contributions of aircraft arrivals and departures to ultrafine particle counts near Los Angeles International Airport

Background: While commercial aircraft are known sources of ultrafine particulate matter (UFP), the relationship between airport activity and local real-time UFP concentrations has not been quantified. Understanding these associations will facilitate interpretation of the exposure and health risk implications of UFP related to aviation emissions. Objectives: We used time-resolved UFP data along with flight activity and meteorological information to determine the contributions of aircraft departures and arrivals to UFP concentrations. Methods: Aircraft flight activity and near-field continuous UFP concentrations (≧ 6. nm) were measured at five monitoring sites over a 42-day field campaign at Los Angeles International Airport (LAX). We developed regression models of UFP concentrations as a function of time-lagged landing and take-off operations (LTO) activity, in the form of arrivals or departures weighted by engine-specific estimates of fuel consumption. Results: Our regression models demonstrate a strong association between departures and elevated total UFP concentrations at the end of the departure runway, with diminishing magnitude and time-lagged impacts with distance from the source. LTO activity contributed a median (95th, 99th percentile) UFP concentration of approximately 150,000particles/cm³ (2,000,000, 7,100,000) at a monitor at the end of the departure runway, versus 19,000particles/cm³ (80,000, 140,000), and 17,000particles/cm³ (50,000, 72,000) for monitors 250m and 500m further downwind, respectively. Conclusions: We demonstrated significant contributions from aircraft departure activities to UFP concentrations in close proximity to departure runways, with evidence of rapid plume evolution in the near field. Our methods can inform source attribution and interpretation of dispersion modeling outputs.