Relationships between cloud condensation nuclei spectra and aerosol particles on a south-north transect of the Indian Ocean

Do anthropogenic emissions affect cloud microphysical properties? One param eter needed to answer the preceding question is a link between the aerosol number distribution and the cloud condensation nuclei (CCN) supersaturation spectrum for polluted and unpolluted air masses. On a south-north cruise i n the Indian Ocean in March of 1998, we found that measured CCN spectra and CCN spectra calculated from the ambient aerosol number distributions disag reed by as much as a factor of 2. The aerosol soluble fraction inferred fro m the relationship between measured and calculated CCN spectra ranged from 0.2 to 0.05 and exhibited a broad minimum at the Intertropical Convergence Zone (ITCZ). The concentration of CCN, non-sea-salt SO42-, NH4+, black carb on. and organic carbon increased by an order of magnitude as we passed thro ugh the ITCZ.