Tunable-diode-laser absorption measurements of H2O2 and HCHO during the Mauna Loa observatory photochemistry experiment.

The tunable diode laser absorption spectrometric technique was employed to measure H 2 O 2 and HCHO during the Mauna Loa Observatory Photochemistry Experiment II fall and winter intensives. Comparisons were made between the measurements made with the TDLAS technique and several other methods. The half-hourly average mixing ratios varies between 1300 pptv and the instrument detection limit of 50 - 100 pptv for H 2 O 2 and between 400 pptv and the instrument detection limit approximately 25 pptv for HCHO. Daily average mixing ratios for H 2 O 2 were 550 +/- 79 pptv (fall) and 540 +/- 80 pptv (winter), and for HCHO were 130 +/- 21 pptv (fall) and 200 +/- 35 (winter). HCHO showed strong diurnal behavior with maxima in the 12:00 - 17:00 time period whereas H 2 O 2 showed essentially no diurnal variation. Clean tropospheric air sampled during downslope conditions between 20:00 and 06:00 had HCHO mixing ratios averaging 80 pptv in the fall and 160 pptv in the winter. These values are considerably lower than model predictions.