| Summary: | Aerosols are well known to have effects on climate and human health. The chemical composition of aerosols in particular has a profound effect on the latter. Many trace elements (e.g. cadmium, lead and arsenic) found in the particulates as well as mercury (existing mostly in the gaseous form) are considered toxic for humans while deposition of these elements poses risks to the ecosystems. Due to emission abatement strategies, emissions of trace elements have significantly reduced in the recent decades. The overall objective of this thesis was to gain knowledge on the different sources as well as the temporal and spatial changes of atmospheric trace elements in Finland. The thesis was focused on the priority trace element pollutants mercury, arsenic, cadmium, nickel and lead. Also, other elements of interest were studied (aluminium, chromium, cobalt, copper, iron, manganese, vanadium, and zinc). Gaseous, particulate and deposition forms of the elements were investigated. The work was concentrated in background areas far away from possible anthropogenic sources; however, urban and industrial sites were also surveyed. The measurement techniques were partially developed or further validated in this thesis, and partially we utilised measurements conducted as a part of international measurement programmes. Sources of trace elements were studied with source apportionment method using positive matrix factorisation (PMF) and enrichment factors. Enrichment factors were used to characterize the source of a pollutant between natural and anthropogenic, and this grouped the elements from mainly crustal (Al, Fe) to highly anthropogenic origin (As, Cd, Pb, Zn) and others in between. PMF produced a more precise analysis of sources for Pallas, in which trace elements were associated with soil, sea emissions, and various long-range transported sources e.g. copper and nickel smelters in Kola Peninsula, Russia. In addition, magnitude of mercury soil and wetland emissions was investigated at one background site with the chamber ...
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