Contactless optical hygrometry in LACIS-T

Abstract. The Fast Infrared Hygrometer (FIRH), employing open-path tunable diode laser absorption spectroscopy at the wavelengths near 1364.6896 nm line, was adapted to perform contactless humidity measurements Turbulent Leipzig Aerosol Cloud Interaction Simulator (LACIS-T), a unique turbulent moist-air wind tunnel. configuration of setup allows for scanning from outside walls tunnel and various positions without need repeated optics adjustments. We identified three factors which significantly influence measurement – self-broadening interference in glass windows parasitic ambient air developed correction methods satisfactorily account these effects. comparison between FIRH reference hygrometer (dew-point mirror MBW 973) indicated good agreement within expected errors across wide range water vapour concentration 1.0–6.1×1017 cm−3 (equivalent dew-point temperature −5.4 +21 ∘C 23 ∘C). High temporal resolution (∼2 kHz) allowed studying fluctuations course intensive mixing two streams had same mean velocity but differed humidity, also including settings mixture can be supersaturated. obtained results contribute improved understanding interpretation cloud formation studies conducted LACIS-T by complementing previous characterizations fields inside