TUNABLE DIODE-LASER ABSORPTION-MEASUREMENTS OF H2O2 AND HCHO DURING THE MAUNA-LOA-OBSERVATORY PHOTOCHEMISTRY EXPERIMENT

The tunable diode laser absorption spectrometric technique was employe d to measure H2O2 and HCHO during the Mauna Loa Observatory Photochemi stry Experiment 2 (MLOPEX 2) fall and winter intensives. Comparisons w ere made between the measurements made with the Tunable Diode Laser Ab sorption Spectrometer (TDLAS) technique and several other methods. The half-hourly average mixing ratios varied between 1300 parts per tilli on by volume (pptv) and the instrument detection limit of 50 - 100 ppt v for H2O2 and between 400 pptv and the instrument detection limit sim ilar to 25 pptv for HCHO. Daily average mixing ratios for H2O2 were 55 0 +/- 79 pptv (fall) and 540 +/- 80 pptv (winter), and for HCHO were 1 30 +/- 21 pptv (fall) and 200 +/- 35 (winter). HCHO showed strong diur nal behaviour with maxima in the 1200 - 1700 time period whereas H2O2 showed essentially no diurnal variation. Clean tropospheric air sample d during downslope conditions between 2000 and 0600 had HCHO mixing ra tios averaging 80 pptv in the fall and 160 pptv in the winter. These v alues are considerably lower than model predictions.