Molecular absorption test at 35 GHz

A laboratory experiment is described which was conducted to find out if the absolute attenuation of a 35 GHz signal by the molecular species hydrogen peroxide, nitric acid, nitrogen dioxide, and nitrous oxide exceeds a threshold value of 0.2 dB/km for concentrations reaching 500 ppm/vol in 1 atm of air. A resonance spectrometer was operated with a detection sensitivity of 0.1 dB/km to obtain pressure scans of attenuation and refraction for the pure gases at low pressures (1 kPa) and for bindary mixtures at atmospheric pressures ( 50 kPa) using nitrogen as the inert, loss-free host gas. Model calculations of attenuation over the frequency range 10 to 50 GHz were performed for natural moist air and hot air ( or = 500 K) under sea level conditions. The measurements of the identified trace gas species produced little (i.e., 0.2 dB/km) additional attenuation.