Sources and chemical composition of atmospheric fine and coarse particles in the Helsinki area

During April 1996-June 1997 size-segregated atmospheric aerosol particles w ere collected at an urban and a rural site in the Helsinki area by utilisin g virtual impactors (VI) and Berner low-pressure impactors (BLPI). In addit ion, VI samples were collected at a semi-urban site during October 1996 May 1997. The average PM2.3 (fine particle) concentrations at the urban and ru ral sites were 11.8 and 8.4 mug/m(3), and the PM2.3-15 (coarse particle) co ncentrations were 12.8 and about 5 mug/m(3), respectively. The difference i n fine particle mass concentrations suggests that on average, more than one third of the line mass at the urban site is of local origin. Evaporation o f fine particle nitrate from the VI Teflon filters during sampling varied s imilarly at the three sites, the average evaporation being about 50-60%. The average fine particle concentrations of the chemical components (25 ele ments and 13 ions) appeared to be fairly similar at the three sites for mos t components. which suggests that despite the long-range transport, the loc al emissions of these components were relatively evenly distributed in the Helsinki area. Exceptions were the average fine particles Ba, Fe, Sb and V concentrations that were clearly highest at the urban site pointing to traf fic (Ba, Fe, Sb) and to combustion of heavy fuel oil (V) as the likely loca l sources. The average coarse particle concentrations for most components w ere highest at the urban site and lowest at the rural site. Average chemical composition of fine particles was fairly similar at the ur ban and rural sites: non-analysed fraction (mainly carbonaceous material an d water) 43% and 37%, sulphate 21% and 25%, crustal matter 12% and 13%, nit rate 12% and 11%, ammonium 9% and 10% and sea-salt 2.5% and 3.2%, respectiv ely. At the semi-urban site also, the average fine particle composition was similar. At the urban site. the year round average composition of coarse p articles was dominated by crustal matter (59%) and the non-analysed compone nts (28%, mainly carbonaceous material and water). while the other contribu tions were much lower: sea-salt 7%, nitrate 4% and sulphate 2%. At the rura l site, the coarse samples were collected in spring and summer and the perc entage was clearly lower for crustal matter (37%) and sea-salt (3%) but hig her for the not-analysed fraction (51%). At the semi-urban site, the averag e composition of coarse particles was nearly identical to that at the urban site. Correlations between the chemical components were calculated separately for fine and coarse particles. In urban fine particles sulphate, ammonium, Tl. oxalate and PM2.3 mass correlated with each other and originated mainly fr om long-range transport. The sea-salt ions Na+, Cl- and Mg2+ formed another group and still another group was formed by the organic anions oxalate, ma lonate, succinate, glutarate and methane sulphonate. Ni and V correlated st rongly pointing to combustion of heavy fuel oil as the likely source. In ad dition, some groups with lower correlations were detected. At the rural and semi-urban sites, the correlating components were rather similar to those at the urban site, although differences were also observed. (C) 2001 Elsevi er Science Ltd. All rights reserved.