Changes in stratospheric water vapor associated with the mount st. Helens eruption

A frost point hygrometer designed for aircraft operation was included in the complement of instruments assembled for the NASA U-2 flights through the plume of Mount St. Helens. Measurements made on the 22 May flight showed the water vapor to be closely associated with the aerosol plume. The water vapor mixing ratio by mass in the plume was as high as 40 x 10(-6). This compares with values of 2 x 10(-6) to 3 x 10(-6) outside of the plume.