Transformation of BTEX compounds emitted by aircraft engines at ground level

Volatile organic compounds, such as benzene, toluene, ethylbenzene and xylenes (BTEX) are emitted during the various aviation activities at ground level, such as take-off, approach and taxiing, that take place at or near airports. In addition to causing adverse health effects, these compounds are precursors of secondary aerosols (SOAs). The expected growth in air traffic in the near future makes it necessary to anticipate and control these emissions. As part of the AVIATOR project (EU Horizon2020), gaseous samples were collected in sorbent tubes and analysed by GC/MS, including emissions of commercial aircraft engines and airport ambient air, to study the evolution and transformation of BTEX. Three sites were selected: the INTA aircraft engine test cell, Ciudad Real and Madrid-Barajas airports. PM was collected on filters and substrates and analysed gravimetrically, with three different samplers: high-volume air sampler, Berner low pressure impactor, and an automated off-line sampler developed by CIEMAT. The ground idle configuration that simulates taxiing manoeuvres (before take-off and after landing) has been identified as a critical contributor to BTEX emissions at airports, with a concentration of over 460 ng L^-1. Benzene is consistently emitted at higher levels than toluene and the emission of both increases with engine acceleration. In the plume, dilution with air decreases not only the concentration of BTEX, but also the prevalence of the compounds, making benzene no longer the dominant compound. Variations in diagnostic ratios and meteorological conditions, as well as sensitivity parameters to PM concentration, may suggest physicochemical transformation of BTEX into SOAs.