Infrared spectrometer measurements of nitric (HNO3) and hydrochloric acid (HCl) from Arrival Heights using a Bruker 120M spectrometer

A Bruker 120M interferometer, a high resolution infrared instrument, was used to measure trace gases in the atmosphere (HNO3, HCl, CH4, N2O, CO, ClONO2) during the early spring from the time the sun returns until early November and also during the winter using moonlight at Arrival Heights. The Bruker replaces the Bomem interferometer previously in place as it has a greater maximum path length and can achieve higher resolutions. Both instruments have two detectors (liquid nitrogen cooled) to cover a range of wavelengths from 2 to 10 �m but the Bruker has provision for taking spectra in six filter passbands, rather than the two of the Bomem. The spectra record the information on the trace gases, contained within, use direct sunlight fed to the instrument with sun tracking mirrors and contain absorption lines of many gases. Quantities of those gases, and in some cases their vertical profiles are determine by fitting the measured spectra to synthetic spectra with least squares or optimal estimation techniques. The data (raw = times and recorded interferograms which are Fourier transformed into spectra, derived = column amounts, and in some cases limited vertical profile information, of atmospheric trace gases) are routinely analysed for HNO3, HCl, CH4, N2O, CO, ClONO2. Plans to extend this include HF, C2H6, HCN in near future. Some moonlight measurements of just HNO3 have also been made.