Volatility of aircraft exhaust ultrafine particles inferred from field measurements at Narita International Airport

Abstract

We conducted field measurements of aerosols near a runway at Narita International Airport (NRT) in February 2018 to characterize the physical and chemical properties of aircraft exhaust ultrafine particles (UFPs; diameter <100 nm). An ultrafine condensation particle counter (UCPC; d50 = 2.5 nm), a condensation particle counter (CPC; d50 = 10 nm), and an engine exhaust particle sizer (EEPS; 6.0–523 nm) were used to measure the particle number concentrations and size distributions in ambient air. The sample flow for the UCPC and CPC was passed through an evaporation tube for heated measurements (150 °C, 250 °C, or 350 °C) or through a bypass tube for unheated measurements. The evaporation tube temperature (Ttube) of 350 °C was used as a threshold point for the separation of volatile and non-volatile particles. The removal efficiency of the volatile particles at intermediate temperatures (<350 °C) was evaluated in the laboratory using triacontane (C30) and tetracontane (C40) as test compounds. The critical temperature at which the laboratory-generated 30-nm C30 and C40 particles were almost entirely removed was ∼130 °C and ∼250 °C, respectively. The particle number concentrations measured by the UCPC, CPC, and EEPS at NRT were used to investigate the volatility of aircraft exhaust UFPs under real-world operating conditions. The number fraction of the non-volatile particles strongly depended on the geometric mean diameter (GMD) of the unheated particle number size distributions, whereas the vaporization temperature of the volatile particles did not exhibit significant dependency on GMD. The particle number fraction remaining, calculated for the selected evaporation tube temperature (Ttube), indicates that ∼50% and ≳ 90% of the volatile particles were removed at Ttube = 150 °C and 250 °C, respectively, on a number basis. These results suggest that a large fraction (more than half by number) of the volatile UFPs emitted from aircraft was equally or less volatile than the 30 nm pure C30 particles and only a small fraction of the volatile UFPs was equally or less volatile than the 30 nm pure C40 particles.