ACTINOMETRIC AND RADIOMETRIC MEASUREMENT AND MODELING OF THE PHOTOLYSIS RATE COEFFICIENT OF OZONE TO O(D-1) DURING MAUNA-LOA-OBSERVATORY PHOTOCHEMISTRY EXPERIMENT 2

The in situ photolysis rate coefficient of O-3 to O(D-1) has been meas ured at Mauna Loa Observatory using a new actinometric instrument base d on the reaction of O(D-1) with N2O and with a hemispherical radiomet er, One minute averaged photolysis rate coefficients were determined w ith an overall uncertainty of approximately +/- 11% at the 1 sigma lev el for the actinometer and +/- 15% at the 1 sigma level for the radiom eter, Over 120 days of data were collected with varying cloud cover, a erosol loadings, and overhead ozone representing the first set of long term measurements. Clear sky solar noon values vary between approxima tely 3.0 x 10(-5) and 4.5 x 10(-5) sec(-1). Modeling of the photolysis rate coefficients was done using a discrete ordinate radiative transf er scheme and results were compared with the actinometric measurements . The quantum yields for O(D-1) production are reevaluated from existi ng data and reported here. The comparisons were done using the quantum yields for the photolysis of ozone recommended by DeMore et al. [1994 ], the newer evaluation of Michelsen et al. [1994], and also with reev aluated values in this paper. An analysis of the measured photolysis r ate coefficient of O-3 to O(D-1) and model simulations of the photolys is rate coefficient data from clear days during the study provides add ed insight into the choice of quantum yield data for use in photochemi cal models of the troposphere.