Observations from aircraft, an island station, and two research vessels showed the presence of an elevated mixed layer or land plume over the Arabian sea during the 1999 intensive field phase of the Indian Ocean Experiment (INDOEX). This layer of about one to two kilometers depth was present above the shallow capping inversion of the well mixed convective marine boundary layer. Much of the transport of the aerosols and gases occurred in this plume. Significant latitudinal variations of aerosols and gases were found in the mixed layer and in the plume. Concentrations of aerosols and ozone were higher in the plume as compared to the marine boundary layer and decreased faster in the as it traveled south towards the equator from the coastline. The development of the land plume and its structure in relation to transport and diffusion of the aerosols is discussed.