A MECHANISM FOR THE FORMATION OF NEW PARTICLES IN THE ATMOSPHERE

The sensitivity of binary nucleation rates of sulfuric acid-water vapo urs in the atmosphere to changes in relative humidity and temperature has led to the suggestion that mixing processes which change either or both may be the cause of many nucleation events. Here it is pointed o ut that very sudden mixing events caused by breaking Kelvin-Helmholtz waves occur preferentially in just those regions where the process wou ld be most effective. The necessary conditions for nucleation by this means are strong thermal and moisture stratification, wind shear and t he presence of a gravity wave of longer period than the Kelvin-Helmhol tz instabilities. Particle production by this process could proceed wi th lower unperturbed nucleation rates than with any slower mixing proc ess. It would be sporadic in time, limited vertically to little more t han the temperature inversion and horizontally to the limited region o f turbulence set up by the breaking waves. Thin double layers of newly formed particles separated vertically by a few hundred metres would o ften result. Others could occur at about the same level at positions d etermined by the wavelength of the initiating disturbance.