Because aerosols are so important to meteorology, visibility, and air quality, it is worth taking a brief look at how aerosol concentrations are distributed globally. On a global scale, aerosols are divided into two broad categories, continental and marine aerosols. These two categories refer to the origin of an aerosol, though you may find concentrations of continental aerosols over the oceans and vice versa. Satellites can track both oceanic and continental aerosol plumes as they are dispersed globally. This allows scientists to identify major source regions and the specific types and concentrations typical over various regions of the earth. For instance, one well known plume is the Sahara dust plume which originates over West Africa and extends across the tropical Atlantic ocean. Another distinct plume originates over the east coast of North America and extends out over the Atlantic. The continental aerosols vary the most by composition and source and include all of those particulate emissions of transportation and industry, as well as wind blown dusts, pollens, and volcanic debris. The marine aerosols consist mainly of salt from sea spray.
On average, the total concentration of aerosols over the oceans is less than the concentration over the continents, due mainly to the limited variety of sources of marine aerosols. For this reason, the concentration over the oceans is also more homogeneous. Also, the number of aerosols that participate in cloud and precipitation formation is significantly less over the oceans than over the continents.
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