The inside of the hut contains all of the instruments that measure NOx (NO + NO2), ozone ( O3) and N2O5.
This is the instrument that measures N2O5. It was developed in our lab by Bill Simpson and other graduate students. It uses a technique called Cavity Ring Down Spectroscopy (CRDS). The instrument has a diode laser at 662 nanometer wavelength(red). The laser light enters the cavity and reflects off the two mirrors; one at each end. The light "rings down" similar to a bell and that time is measured. When there is N2O5 present it absorbs at 662 nanometers and the ringdown time is less. We are able to measure the amount, or mixing ratio, of N2O5 in the atmosphere in pptv (parts per trillion by volume) from the difference in these two ring down times.