Ozone (O3) and nitrogen dioxide (NO2) are two trace gases in the stratosphere that interact to have an important effect on the radiation balance. The spatial and temporal variation in these gases (total column over time), whose quantities in the stratosphere are controlled by photochemistry and by horizontal and vertical transport processes are monitored annually with visible wavelength ... spectrometers. A spectrometer was installed at Arrival Heights and measurements are made using scattered light in the zenith sky when the solar zenith angle is between 80 and 96 degrees. A variety of instruments have been used since first measurements began and each instrument has been serviced and replaced at various intervals. The long term data set (raw data = times and recorded spectra of scattered light, derived = column amount of NO2 and O3) is analysed for trends impressed by solar cycle variability, quasi-biennial oscillation effects and volcanic perturbations. The system of scanning spectrometers at Arrival Heights was supplemented by a complete backup system (at Scott Base in January 1994) to minimise the chance of this long term record being broken.