Temporal changes of Mount Pinatubo aerosol characteristics over northern midlatitudes derived from SAGE II extinction measurements

The June 12-16, 1991, eruption of Mount Pinatubo in the Philippines injected an estimated 20 Mt of sulfur dioxide gas well into the stratosphere and is the largest volcanic event recorded in recent history. The Stratospheric Aerosol and Gas Experiment (SAGE) II satellite has provided unprecedented information On the evolution of the Pinatubo aerosol since its eruption. The Pinatubo aerosol size distributions are inferred from SAGE II extinction measurements using a randomized minimization search technique in the radii range of 0.1-0.8 mu m in 0.1-mu m increments. The Pinatubo aerosol characteristics between 13 and 30 km and columnar characteristics in a unit column between 15 and 25 km are then derived. The latitudinal span is between 30 degrees and 60 degrees N from March 1991 to March 1994. During this period, the maximum surface area was observed to exceed 50 mu m(2) cm(-3). The vertically averaged surface areas were of the order of 27.74 +/- 12 mu m(2) cm(-3) in March 1993 at a height of 14.5 km. The corresponding averaged mass loading was of the order of 4.23 +/- 1.37 mu g m(-3). During March 1994, the peak surface areas and mass loading at 14.5 km were of the order of 9.85 +/- 3.87 mu m(2) cm(-3) and 1.02 +/- 0.28 mu g m(-3), respectively, still larger with respect to the volcanically cm unperturbed values of 0.98 +/- 0.54 mu m(2) cm(-3) and 0.12 +/- 0.04 mu g m(-3) observed during cm March 1991. Columnar mass loading, surface area, and number concentrations have approached preeruption background levels, whereas the columnar mean effective radius is still 2-3 times greater as of March 1994.