Tropospheric distributions of H₂SO₄-H₂O binary nucleation rates are calculated from a 3D model with DMS chemistry. Two mechanisms are used that include and exclude an SO₂-independent H₂SO₄ production path. In the lower troposphere, the SO₂-independent path generates extra H₂SO₄ and, consequently, much higher aerosol nucleation rates. However, these rates are less than 10⁻⁵ particles cm⁻³ s⁻¹ in most of the lower troposphere, which indicates that DMS oxidation does not lead to appreciable aerosol formation there. In the upper troposphere, binary nucleation is fairly insensitive to the mechanism differences, with both yielding rates that exceed 1 particle cm⁻³ s⁻¹ in the upper tropics. These large upper tropospheric nucleation rates imply that the DMS cycle may have served as an important source of aerosols to the troposphere and stratosphere during preindustrial and volcanically-quiescent periods, or during modern periods in clean marine regions where anthropogenic SO₂ and H₂SO₄ are relatively low.

© 2003 American Geophysical Union