Size distributions of aerosols over the Indian Ocean

Concentration and size distribution of aerosol particles in the size range of 0.5 to 20.0 mu m were measured over the Indian Ocean during January 23 to March 31, 2004. Total aerosol concentration showed the North-to-South positive gradient with latitude over the Indian Ocean North of the Inter Tropical Convergence Zone (ITCZ). Minimum concentration of aerosols was observed immediately South of the ITCZ and it increased on either side of the ITCZ. Contrary to being monomodal in shape in this size range as is generally expected over open ocean, the aerosol size distributions followed the Junge's power law and show the transport of aerosols from the Indian subcontinent to North of the ITCZ, even though several hundreds of kilometers away from the Indian coastline. Aerosols South of the ITCZ exhibited monomodal size distributions which were typical of marine aerosols in the pristine environments. Aerosol size distributions in the roaring forties clearly showed the generation of sea-salt particles due to the wave breaking activity in this region of high winds. Abundance of particles of < 1.0 mu m diameter dominated over the Indian Ocean North of the ITCZ.