3. Distribution

Given the distribution of aerosol sources and its lifetime in the atmosphere, its spatial and temporal distribution is highly heterogeneous. Its effect on the equilibrium of the coupled Earth/atmosphere system is therefore preferentially regional. A rough average of the environmental impacts of aerosol, such as radiative impacts, is certainly an indicator, but can only be a small part of a wider reality.

The global distribution of aerosol is well illustrated in figure 4 . This is a map of average optical thickness at a wavelength of 550 nm for the month of August 2003. It has been deduced from satellite observations by the Modis (moderate resolution imaging spectroradiometer) instrument on board a polar-orbiting...