17.2 Human activities have increased air pollution Volcano Fig 17. 3 the cloud of sulfur dioxide generated by the June 15, 1991 eruption of Mount Pinatubo reached India in four days. (the black strips are where satellite data are missing ) by July 27, the sulfur dioxide cloud had traveled around the globe17.2 Human activities have increased air pollution • Volcano Fig 17.3 the cloud of sulfur dioxide generated by the June 15,1991, eruption of Mount Pinatubo reached India in four days. (the black strips are where satellite data are missing.) by July 27, the sulfur dioxide cloud had traveled around the globe