Measurement of peroxyacetyl nitrate NO2 and NOx by using a gas chromatograph with a luminol-based detector

摘要

A commercial instrument for measuring PAN (peroxyacetyl nitrate), NO$- 2$/, and optionally, NOx, is described. It is based on a gas chromatograph (GC), and uses a Luminox$+R$/ luminol detector following conversion of the PAN to NO$-2$/. A detection limit (based on a peak height of 3 $MUL noise) of 30 pptV is achieved for injections made every five minutes. The instrument is computer driven and contains its own peak integrator and graphics output. No interferences have been identified, including chlorinated hydrocarbons, NO$-2$/ and ozone. However, the PAN analog peroxypropanyl nitrate (PPN) is not fully resolved from PAN. The maintenance interval is monthly. The calibration of the instruments is relatively easy: known mixing ratios of NO$-2$/ in air are used to calibrate the sample injection system and Luminox$+R$/ detector. The passage of PAN through the column and the subsequent conversion of PAN to NO$-2$/ has been found to be stable over times of one year, and is reproducible between instruments. Atmospheric measurements for PAN have been carried out for both very polluted environments and very clean environments. The results from a month long formal intercomparison between the Luminox$+R$/ 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.