Determination of NO_x emissions from Frankfurt Airport by optical spectroscopy (DOAS) – A feasibility study

Abstract. Standard methods like in-situ measurements can hardly register NO_x (= NO + NO₂) emissions from aircrafts during take-off, when engines run at high load and thus an important amount of fuel is consumed and most of the harmful emissions are produced . The goal of this work is to show that it is possible to measure aircraft emissions generated during take-off (and initial part of the climb) by a remote spectroscopic method like automobile – based – Differential Optical Absorption Spectroscopy (Mobile-DOAS), which uses scattered solar radiation in the blue spectral range (around 445 nm). In order to test its feasibility, total column measurements of NO₂ encircling Frankfurt Airport were carried out on 23 February 2012 using Mobile-DOAS. Also, NO_x fluxes were derived from the NO₂ observations. Unlike standard mobile-DOAS measures using a spectrometer looking at zenith, the measurements were performed looking at 22° elevation angle leading to a roughly two to three times higher sensitivity compared to zenith observations. The origin of the observed NO₂ is discussed and the total NO_x fluxes are calculated. As result of three round-trips encircling the Frankfurt Airport, the mean NO_x flux was found to correlate with the number of aircrafts taking-off. Our results demonstrate that mobile-DOAS method is suitable for quantifying emissions from airports and to study their impact in the planetary boundary layer, which is most relevant concerning the impact on the environment and the human health.