Selective measurements of NO, NO2 and NOy in the free troposphere using quantum cascade laser spectroscopy

A quantum cascade laser based absorption spectrometer for continuous and direct measurements of NO and NO2 was employed at the high-altitude monitoring site Jungfraujoch (3580 m a.s.l., Switzerland) during a three-month campaign in spring/summer 2012. The total reactive nitrogen, NOy, was also measured in the form of NO after conversion on a gold catalyst. The aim was to assess the suitability of the instrument for long-term monitoring of the main reactive nitrogen species under predominantly free tropospheric air conditions. A precision (1 sigma) of 10 and 3 ppt for NO and NO2 was achieved under field conditions after 180 s averaging time. The linear dynamic range of the instrument has been verified for both species from the detection limit up to 45 ppb. The spectrometer shared a common sampling inlet with a chemiluminescence-based analyzer. The comparison of the time series shows excellent agreement between the two techniques and demonstrates the adequacy of the laser spectroscopic approach for this kind of demanding environmental applications.