Composition and origins of aerosol during a high PM10 episode in Finland

We investigated the sources of a PM10 episode in September 2001 on the coasts of the Gulf of Finland. The episode lasted six days with the peak phase lasting over 14 hours. The highest hourly PM10 concentration was 190 ug m–3. Exceptional meteorological conditions strongly influenced the course of the episode. Very warm air masses came from central Asia forming a stable inversion over the Gulf of Finland. Dust emissions from the Estonian and Russian oil-shale burning industrial areas near the southeastern coast of the Gulf of Finland were transported over the Gulf above the inversion layer. After reaching the northern coast the PM was mixed down by convection and partly by gravitation, and then transported westwards along the coastline. The chemical analyses by SEM/EDX and IC indicated that the particles had both the characteristics of the oil-shale burning emissions and soil dust. Windy conditions in the Kazakhstan Ryn Peski desert raised soil dust into the air. This dust was transported towards Scandinavia and mixed with the anthropogenic emissions. Such large quantities of coarse particles from foreign sources have not been observed earlier in Helsinki.