WE PROPOSE TO INVESTIGATE THE CHEMISTRY OF CARBON CHLORINE AND SULFUR SPECIES IN THEMIDDLE ATMOSPHERE OF VENUS. THE PROPOSED RESEARCH TAKES ADVANTAGE OF THE DATA THAT ARE AND WILLBECOME AVAILABLE FROM VENUS EXPRESS TO ADDRESS A NUMBER OF KEY ISSUES RELATED TO THE CHEMICALCOMPOSITION OF THE ATMOSPHERE OF VENUS. THE PROPOSED TASKS INCLUDE THE PHOTOCHEMISTRY OF THEMIDDLE ATMOSPHERE THAT RELATES TO CO2 STABILITY AND PRODUCTION OF H2S04 AEROSOLS AND POLYSULFUR(SX). NEW CHEMISTRY WILL INCLUDE HETEROGENEOUS REACTIONS ON THE SURFACE OF H2S04 AEROSOLS ANDSX AND THEIR IMPACT ON THE DISTRIBUTION OF OCS AND CO OBSERVED BY VENUS EXPRESS. AN INNOVATIVE TRANSPORT SCHEME WILL BE USED TO EXTEND THE ONE-DIMENSIONAL CHEMICAL MODEL TO TWO-DIMENSIONS(2-D ALTITUDE AND LATITUDE) TO ACCOUNT FOR THE EXCHANGE OF LOWER AND UPPER ATMOSPHERES.RECENT HIGH QUALITY DATA OF OCS FROM GROUND-BASED AND VENUS EXPRESS OBSERVATIONSPROVIDE A UNIQUE OPPORTUNITY TO TEST OUR UNDERSTANDING OF CHEMISTRY AND TRANSPORT IN THEATMOSPHERE OF VENUS. OCS IS PRODUCED BY HETEROGENEOUS REACTIONS ON THE SURFACE; THE MIDDLEATMOSPHERE IS A NET SINK FOR OCS. POLYSULFUR (SX) APPEARS TO PLAY A CRUCIAL ROLE IN THEPHOTOSENSITIZED DISSOCIATION OF OCS. AN INNOVATIVE CHEMICAL SCHEME INVOLVING SN WHERE NVARIES FROM 1 TO 8 IS PROPOSED (SN FOR N 8 IS TREATED AS SX). THE SPATIAL DISTRIBUTION OF OCS INTHE MIDDLE ATMOSPHERE OF VENUS REFLECTS A SENSITIVE BALANCE BETWEEN CHEMISTRY AND TRANSPORT.USING OUR UPDATED PHOTOCHEMICAL MODEL AND WINDS FROM LEE ET AL.'S (2007) GENERAL CIRCULATIONMODEL WE WILL EXPLORE THE NEW CHEMISTRY IN OUR TWO-DIMENSIONAL CHEMISTRY-TRANSPORT MODEL.THE MODELING TASK WILL BE EXTENDED TO THE STUDY OF CO AND OTHER SPECIES (E.G. H20) AND THERESULTS WILL BE COMPARED WITH OBSERVATIONS.THE PRINCIPAL RESERVOIRS OF HYDROGEN ON VENUS ARE H20 AND HCL. PHOTOLYSIS OF H2O ANDHCI PROVIDES THE MAJOR SOURCE OF H ATOMS THAT ESCAPE FROM VENUS. THE ISOTOPIC CHEMISTRY THATRESULTS IN THE PREFERENTIAL RELEASE OF H ATOMS OVER D ATOMS WILL BE INVESTIGATED. BERTAUX ET AL.(2007) PROVIDED NEW INFORMATION FROM VENUS EXPRESS TO CONSTRAIN THE ABUNDANCES OF H20 ANDHDO. NEW PROCESSES OF ISOTOPIC FRACTION DUE TO FORMATION OF H2S04 WILL BE INCLUDE.IMPLICATIONS FOR ATMOSPHERIC EVOLUTION WILL BE EXPLORED.A RADIATIVE MODEL WILL USED TO RECONCILE THE NEW MEASUREMENTS OF HCL FROM VENUSEXPRESS (VANDAELE ET AL. 2008) WITH EARLIER GROUND-BASED OBSERVATIONS (CONNES ET AL. 1967). THEIMPLICATIONS OF THE LOWER HCL CONCENTRATIONS FROM VENUS EXPRESS FOR THE CHEMISTRY OF VENUSWILL BE EXPLORED.