A diode laser spectrometer for the in situ measurement of the HNO3 contentof polar stratospheric clouds

A new instrument realized for measuring the HNO3 concentration in air is de scribed. The device is a midinfrared absorption spectrometer based on a tun able diode laser and a multipass absorption cell. The instrument is specifi cally designed for airborne operation on board the M-55 Geophysica, in the frame of the Airborne Polar Experiment project, taking into account all the related environmental and operational constraints. The device is part of a complete measurement package for the measurement of the chemical content o f the polar stratospheric clouds and other atmospheric aerosols. Furthermor e, it can be used as a stand-alone detector of molecular trace gases. The p rimary purpose of the instrument is to perform in situ diagnostic measureme nts in the upper troposphere-lower stratosphere. Design criteria include a new optical setup, one much less sensitive to the vibration and thermal str esses with respect to the conventional diode laser spectrometers. Furthermo re, the authors developed a novel detection scheme for quicker acquisition and better signal-to-noise ratio. This paper reports calibration and testin g measurements, including a detection lower limit both for the HNO3 and amm onia. This last gas is used as a wavelength and absorption reference.