Laser photoacoustic detection of nitrogen dioxide in the gas-phase titration of nitric oxide with ozone

Gas-phase titration (GPT) studies of nitric oxide (NO) with ozone (O/sub 3/) were carried out over a 1 year time span. In these studies, NO and O/sub 3/ concentrations were measured with conventional techniques of chemiluminescence and uv absorption photometry, respectively. Nitrogen dioxide concentrations (NO/sub 2/) also measured during the course of titration were carried out by use of a photoacoustic detection system, a method in which NO/sub 2/ was measured directly without an interfering response from NO. Excellent agreement in NO and NO/sub 2/ concentration changes during titration has been demonstrated throughout this study. The corresponding O/sub 3/ measurements, however, were found to average 3.6% lower. Additional studies, both experimental and photochemical modeling of air stream impurities, could not account for this discrepancy.