Vertical profiles of volcanic aerosol and polar stratospheric clouds above Kiruna, Sweden: Winters 1993 and 1995

Vertical profiles of aerosol were measured in February 1993, and January - March 1995 using balloon-borne particle counters released from Kiruna, Sweden. Condensation nuclei (CN) and aerosol with radii greater than or equal to 0.15 - 10.0 mu m were measured in 8-12 size classes. The three flights in 1993 were within the polar vortex. Temperatures were below polar stratospheric cloud (PSC) threshold temperatures on one night and a thin PSC was observed. The volcanic aerosol in the 1993 vortex was similar to that in 1992. In 1993, surface areas were 10 - 20 mu m(2) cm(-3) and volumes 1 - 3 mu m(3) cm(-3). In 1995 three of five nights were within the polar vortex. The volcanic aerosol had decreased to 3 - 7 mu m(2) cm(-3) and 0.1 - 0.4 mu m(3) cm(-3). The top of the volcanic aerosol layer in both years was near 500 K potential temperature (similar to 20 km). A thick nitric acid and water PSC was observed in January 1995. In the thickest region of this PSC nearly all CN were observed to be activated, and surface areas of 5 - 10 mu m(2) cm(-3) were calculated. The volumes observed in this PSC were closer to what would be expected for particles composed of nitric acid trihydrate than for ternary solution droplets. In 1993 the opposite was observed, the volumes in the thin PSC were closer to what would be expected for ternary solution droplets.