NUCLEATION IN THE MSA WATER-VAPOR SYSTEM

The threshold concentrations of gaseous methane sulfonic acid (MSA) required for homogeneous and heterogeneous nucleation of MSA solution droplets in the MSA-water system have been calculated as a function of environmental relative humidity. The MSA concentration required to supersaturate the atmosphere (with respect to aqueous MSA solutions) at 80% r. h. is of the order of 10** minus **1**2 atm (1 pptv), whereas the concentration required for spontaneous production of new MSA aerosol is of the order of 10** minus **8 atm (10 ppbv). The calculations also show a strong dependence of the saturation curve on relative humidity. At 80% r. h. 1 pptv MSA vapor supersaturates the atmosphere, whereas at 10% r. h. about 5 ppbv is required to supersaturate the environment. The role which the conversion of dimethylsulfide (DMS) to MSA and H//2SO//4 might play in the formation and growth of sub- mu m particles in remote oceanic regions is discussed.