FUNDAMENTAL OZONE PHOTOCHEMISTRY IN THE REMOTE MARINE BOUNDARY-LAYER - THE SOAPEX EXPERIMENT, MEASUREMENT AND THEORY

During the Austral summer of 1995, a series of measurements were made as part of the SOAPEX (Southern Ocean Atmospheric Photochemistry EXper iment) campaign at the Cape Grim Baseline Air Pollution station (41 de grees S) on the north western tip of Tasmania, Australia. These measur ements included peroxy radicals, photolysis parameters, speciated pero xides, NOx and other related chemical quantities. The climatology of C ape Grim is such that it frequently receives ''clean'' remote marine b oundary layer air off the Southern Ocean and in this air in summer, th ere is clear evidence for the net photochemical destruction of ozone. The factors influencing the photochemical control of ozone are investi gated by means of the relationship between peroxy radicals and j(o(1D) ). From the levels of peroxy radicals and j(o(1D)), mid-day hydroxyl r adical concentrations of (6 +/- 0.9) x 10(6) molecules cm(-3) are calc ulated,in agreement with other estimates in this region. An apparent d iscrepancy between measured and calculated peroxy radical levels in th e ''clean'' atmosphere is investigated both from theoretical treatment s and from the speciated peroxide record. The possible role of aerosol s in the suppression of peroxy radicals are also discussed. Using simp le photochemical theory the relative roles of photolysis and reaction with radicals are investigated in the observed -2.5 ppbv per day photo chemical destruction of ozone. Measured values of j(o(1D)), calculated [OH] and the corrected peroxy radical concentration are used successf ully to produce a simple fit to the ozone diurnal, illustrating the ma gnitude of the various contributing components, i.e. photolysis and re action. (C) 1998 Elsevier Science Ltd. All rights reserved.