In situ measurements of Pinatubo aerosol over Kiruna on four days between 18 January and 13 February 1992

Vertical profiles of aerosol were measured on 18 and 27 January and 4 and 13 February, 1992, using balloonborne particle counters released from Esrange (68°N, 21°E) near Kiruna, Sweden. Condensation nuclei (CN) and aerosol with radii ≥ 0.15 µm, in 8 size classes, were measured. In the lower stratosphere concentrations of the larger particles were greater, by factors of 10 to 100, than those measured on flights from Esrange in January and February 1991. CN concentrations in the two years showed no pronounced differences. The bulk of the particles were volcanic aerosol from the eruption of Mt. Pinatubo. On the first three flights, in air polewards of the stratospheric jet stream, there was little volcanic aerosol above 20 km, although a highly structured polar stratospheric cloud (PSC) was detected above the volcanic layer on 27 January. In the main volcanic layer, below about 16 km, the aerosol constituted 10 to 60 ppbm sulfuric acid, with a surface area density of 5 to 10 µm² cm−3, based on lognormal size distributions fit to the concentration measurements. These are respectively 50 and 10 times larger than the mass and surface area densities found in 1991. On the last flight in air equatorward of the jet stream, volcanic aerosol was detected up to 27 km, with peak values, near 20 km, of 100 ppbm sulfuric acid and 20 µm² cm−3 surface area density. These are similar to observations in the mid‐latitudes at that time.