Note that the SO2 scale used is normalized to the maximum SO2 column
measured on each day (Normalized SO2 column = [SO2 column/Max SO2 column]*100).
On May 20, 2006 a major lava dome collapse at the Soufriere Hills volcano on Montserrat (West Indies) triggered an explosive emission of volcanic gases. The resulting gas cloud penetrated the stratosphere, reaching an altitude of ~20 km. Sulfur dioxide (SO2) in this cloud was tracked by OMI for 3 weeks as it moved westwards across the Pacific, before finally dissipating below detection limits over the Indian Ocean on June 11.
The CALIPSO lidar saw the volcanic sulfate aerosol plume on the orbit pass shown below. SO2 is a gas, but it slowly turns to sulfuric acid droplets as SO2 reacts with OH in the stratosphere. The CALIPSO aerosol lidar spotted the small cloud of droplets forming in side the SO2 plume that OMI sees. CALIPSO is orbiting a few minutes ahead of Aura.