Use of atmospheric elemental size distributions in estimating aerosol sources in the Helsinki area

• Published in: Atmospheric environment (1994) Vol. 35; no. 32; pp. 5537 - 5551
• Main Authors: Pakkanen, Tuomo A, Kerminen, Veli-Matti, Korhonen, Christina H, Hillamo, Risto E, Aarnio, Päivi, Koskentalo, Tarja, Maenhaut, Willy
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2001
• Subjects: Atmosphere; Elements; Local; Long-range transport; Rural; Size distribution; Sources; Urban; Finland, Uusimaa, Helsinki; Finland, Helsinki; Rural; Urban; Size distribution; Atmosphere; Local; Elements; Sources; Long-range transport
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/S1352-2310(01)00232-1

In June 1996–June 1997 Berner impactors were used in the Helsinki area to measure size distributions of atmospheric aerosols simultaneously at an urban and at a rural site. Ten sample pairs were collected in the size range of 0.03–15.7 μm of equivalent aerodynamic diameter (EAD). Average size distributions at the two sites were calculated for 29 elements, particulate mass, and sulphate. At both sites especially sulphate, As, B, Bi, Cd, Ni, Tl, and V were enriched in fine particles (EAD<2.3 μm). In order to estimate local fine-particle sources of the various chemical components, the similarities and dissimilarities in the accumulation-mode parameters were studied separately for both sites. It was observed that often in different samples, different components had similar accumulation modes. At both sites, particulate mass, As, and Pb had similar accumulation modes to sulphate which suggests that long-range transport (LRT) is important for these components. V, Ni, Mo, and Co formed another group of similar accumulation modes at both sites suggesting that these elements largely originated from local and regional oil combustion. In addition, other groups of similar accumulation modes were observed but these groups were different between the sites. The meteorological parameters indicated that seven sample pairs formed a subset of the data in which the local emissions of the Helsinki area were transported to the urban site but not to the rural site. For this subset the rural fine-particle concentrations were considered to represent an upper limit estimate for the LRT. These upper limit LRT estimations were further improved by utilising the quantitative relative size distributions (QRSD) method at the rural site. The QRSD method supposes that in the fine-particle size range the LRT fractions of all chemical components have a similar shape in their size distributions. Fine-particle sulphate is typically long-range transported, and was therefore selected as the model component that represents the shape of LRT material. Sulphate size distribution was then scaled to give an estimation of the LRT contribution of each component at the rural site. These rural “sulphate scaled” LRT estimates were subtracted from the corresponding urban concentrations to give the local contributions (ng/m 3) downwind of the Helsinki area. In particles with EAD below 2.3 μm, the highest absolute and relative downwind local contributions were observed for several common sea-salt and road-dust components. Also the combustion-related elements Ni and V showed fairly high downwind local contributions. Because of the limited number of samples, the local and LRT contributions were not estimated for different wind directions.