Atmospheric black carbon in Helsinki

Atmospheric fine particle black carbon (BC) was measured close to downtown of Helsinki, during November 1996-June 1997. The average BC concentrations were 1.5 mu g m(-3) for working days, 1.2 mu g m(-3) for Saturdays, and abo ut 1 mu g m(-3) for Sundays and public holidays. The overall average BC con centration was equal to 1.38 mu g m(-3) and its average contribution to fin e particle mass equal to 19%. On working days BC concentrations showed a cl ear diurnal variation with the highest hourly average Values occurring duri ng the morning (2.7 mu g m(-3)) and evening (1.9 mu g m(-3)) rush hours. Co ntribution of the long-range transport to the BC was estimated to be on ave rage about 0.4 mu g m(-3), which is believed to represent the average regio nal background over southern Finland. However, this transport was very diff erent from different geographical regions: from the densely populated areas of East- and Central-Europe it was about 0.8 mu g m(-3), while in northerl y and northwesterly air masses it was only about 0.15 mu g m(-3). Local tra ffic was by far the most important local BC source contributing about 63, 5 4 and 44% on working days, Saturdays and Sundays, respectively. Other local sources were largely masked by the traffic and their contribution was esti mated roughly to be of the order of 10%. The rest of BC was attributed to l ong-range transport. (C) 2000 Elsevier Science Ltd. All rights reserved.