International audienceThe variability of stratospheric aerosol loading between 1985 and 2010 is explored with measurements from SAGE II, CALIPSO, GOMOS/ENVISAT, and OSIRIS/Odin space-based instruments. We find that, following the 1991 eruption of Mount Pinatubo, stratospheric aerosol levels increased by as much as two orders of magnitude and only reached "background levels" between 1998 and 2002. From 2002 onwards, a systematic increase has been reported by a number of investigators. Recently, the trend, based on ground-based lidar measurements, has been tentatively attributed to an increase of SO2 entering the stratosphere associated with coal burning in Southeast Asia. However, we demonstrate with these satellite measurements that the observed trend is mainly driven by a series of moderate but increasingly intense volcanic eruptions primarily at tropical latitudes. These events injected sulfur directly to altitudes between 18 and 20 km. The resulting aerosol particles are slowly lofted into the middle stratosphere by the Brewer-Dobson circulation and are eventually transported to higher latitudes

[1] We review the standard nitrogen dioxide (NO 2 ) data product (Version 1.0.), which is based on measurements made in the spectral region 415-465 nm by the Ozone Monitoring Instrument (OMI) on the NASA Earth Observing System-Aura satellite. A number of ground-and aircraft-based measurements have been used to validate the data product's three principal quantities: stratospheric, tropospheric, and total NO 2 column densities under nearly or completely cloud-free conditions. The validation of OMI NO 2 is complicated by a number of factors, the greatest of which is that the OMI observations effectively average the NO 2 over its field of view (minimum 340 km 2 ), while a ground-based instrument samples at a single point. The tropospheric NO 2 field is often very inhomogeneous, varying significantly over tens to hundreds of meters, and ranges from <10 15 cm À2 over remote, rural areas to >10 16 cm À2 over urban and industrial areas. Because of OMI's areal averaging, when validation measurements are made near NO 2 sources the OMI measurements are expected to underestimate the ground-based, and this is indeed seen. Further, we use several different instruments, both new and mature, which might give inconsistent NO 2 amounts; the correlations between nearby instruments is 0.8-0.9. Finally, many of the validation data sets are quite small and span a very short length of time; this limits the statistical conclusions that can be drawn from them. Despite these factors, good agreement is generally seen between the OMI and ground-based measurements, with OMI stratospheric NO 2 underestimated by about 14% and total and tropospheric columns underestimated by 15-30%. Typical correlations between OMI NO 2 and ground-based measurements are generally >0.6.