Abstract : It is expected that the aerosols in the stratosphere, are predominantly sulfates resulting from natural or anthropogenic sources of precursor gases mainly: carbonyl sulfide (OCS), sulfur dioxide (SO2). Sulphate aerosols are regarded as the main constituent of the "Junge layer" between the tropopause and about 30 km. This assumption is regularly challenged by detection of solid aerosols with aircraft and balloon
measurements. The direct injection of gaseous SO2 into the stratosphere by major volcanic eruptions is likely to generate significant amounts of sulfate aerosols that can stay for several years. Recently, Vernier et al. (2011) have shown from satellite measurements that moderate eruptions modulate the aerosol content during periods not influenced by a major volcanic eruption, called "background" periods.
Surprisingly, the radiative impact of the background stratospheric aerosols over the last decade, has been found to be significant with a counterbalance to global warming (Solomon et al., 2011).
