THEORETICAL, ACTINOMETRIC, AND RADIOMETRIC DETERMINATIONS OF THE PHOTOLYSIS RATE COEFFICIENT OF NO2 DURING THE MAUNA-LOA-OBSERVATORY PHOTOCHEMISTRY EXPERIMENT 2

Measurements of the photolysis rate coefficient of NO2 (jNO(2)) were m ade using a chemical actinometer during the fall (September 15 to Octo ber 23, 1991), winter (January 15 to February 15, 1992), spring (April 15 to May 15, 1992), and summer (July 15 to August 15, 1992) intensiv es during the second Mauna Loa Observatory Photochemistry Experiment ( MLOPEX 2), Hawaii. The measured clear sky jNO(2) values of MLOPEX 2 fo r all four intensives have substantially increased over the measured j NO(2) values of MLOPEX 1 (May, 1988); a 37% increase occurs in midday clear sky jNO(2) from the spring intensive of MLOPEX 1 to the spring i ntensive of MLOPEX 2. The ratio of actinometer measurements to theoret ical calculations of jNO(2) are 1.44+/-0.03, 1.45+/-0.02, 1.43+/-0.03, and 1.34+/-0.02 for the fall, winter, spring, and summer intensives, respectively. Inclusion of stratospheric aerosols or aerosols of any r easonable optical parameters in a detailed discrete ordinate model can not account for the discrepancy between measurements and model. The ph otolysis rate coefficient of NO2 is also derived from simultaneous mea surements of the ultraviolet irradiance measured with an Eppley radiom eter using a semiempirical relationship for each of the four intensive s. A simplified cloud model is proposed to explain jNO(2) values that exceed clear sky values during days that have partial cloud coverage.