PHYSICOCHEMICAL MODELING OF THE FIRST AEROSOL CHARACTERIZATION EXPERIMENT (ACE-1) LAGRANGIAN-B - 2 - DMS EMISSION, TRANSPORT AND OXIDATION AT THE MESOSCALE

A three-dimensional mesoscale meteorological model was used to study t he interplay between the dynamical (turbulent mixing and advection) an d physico-chemical (sea-air flux and photochemical sink by OH) process es that control dimethylsulfide DMS concentrations and their distribut ion in the marine boundary layer (MBL) during the First Aerosol Charac terization Experiment ACE 1, Atmospheric DMS concentrations were const rained using observed seawater DMS concentrations and box model derive d OH concentrations. Lateral boundary values of dynamical parameters w ere derived from the 6-hourly meteorological analysis of the European Centre for Medium-Range Weather Forecasts. Calculated DMS concentratio ns, wind speed and direction, and cloud cover were compared with measu rements made aboard the RN Discoverer and on the three NCAR/C130 aircr aft flights during the LagB experiment. Model-generated atmospheric DM S concentrations agreed with the DMS observations from the NCAR/C130 a ircraft flights during the LagB experiment (R-2 = 0.69) assuming OH is the only oxidant and DMS flux parameterization based on Liss and Merl ivat [1986], Comparison with Eulerian measurements made aboard the RN Discoverer showed that the model simulated the range of observed value s but not the hour-to-hour variation observed in the atmospheric DMS c oncentrations. Part of the discrepancy was attributed to uncertainties in DMS sea-to-air transfer velocity, small scale features of seawater DMS that are beyond the model resolution, and uncertainties in the ve nting of the boundary layer by shallow clouds. A quantitative budget a t the ship location revealed a strong impact of advection processes in determining DMS levels and temporal evolution. The three-dimensional mesoscale meteorological model was also used to estimate the effect of the low spatial resolution used in global models on seawater DMS conc entrations and atmospheric OH concentrations.