A commercial instrument for measuring PAN (peroxyacetyl nitrate), NO2, and optionally, NOx, is described. It is based on a gas chromatograph (GC), and uses a LuminoxR luminol detector following conversion of the PAN to NO2. A detection limit (based on a peak height of 3 X noise) of 30 pptV is achieved for injections made every five minutes. The instrument is computer driven and contains its own peak integrator and graphics output. No interferences have been identified, including chlorinated hydrocarbons, NO2 and ozone. However, the PAN analog peroxypropanyl nitrate (PPN) is not fully resolved from PAN. The maintenance interval is monthly. The calibration of the instruments is relatively easy: known mixing ratios of NO2 in air are used to calibrate the sample injection system and LuminoxR detector. The passage of PAN through the column and the subsequent conversion of PAN to NO2 has been found to be stable over times of one year, and is reproducible between instruments. Atmospheric measurements for PAN have been carried out for both very polluted environments and very clean environments. The results from a month long formal intercomparison between the LuminoxR PAN and two GCs equipped with electron capture detectors is presented. Those results demonstrate that the luminol based PAN detector can yield accurate measurements of ambient PAN concentrations. A method for calibrating PAN instruments in the field is described.