Atmospheric Environment 35 (2001) 4357–4366 Change of the ambient particle size distribution in East Germany between 1993 and 1999 M. Pitz a,b , W.G. Kreyling c , B. H . olscher b , J. Cyrys a,b , H.E. Wichmann a,b , J. Heinrich b, * a Ludwig-Maximilians-University, Institute of Medical Data Management, Biometrics and Epidemiology, Munich, Germany b GSF National Research Center for Environment and Health, Institute of Epidemiology, Postfach 1129, D 85758 Neuherberg/Munich, Germany c GSF National Research Center for Environment and Health, Institute for Inhalation Biology, Neuherberg/Munich, Germany Received 7 November 2000; received in revised form 4 April 2001; accepted 9 April 2001 Abstract Size distribution of particle number concentrations in the geometric equivalent diameter range 0.01–2.5 mm were determined in three communities, Zerbst, Bitterfeld and Hettstedt of the state of Sachsen-Anhalt in Eastern Germany, in the first half of 1993 and 1999. A Mobile Aerosol Spectrometer (MAS) consisting of a differential mobility particle spectrometer (DMPS) and a laser aerosol spectrometer (LAS-X) were used for size-selective particle number concentration measurements from which mass concentrations were derived based on an apparent mean density of the ambient aerosol of the closely situated city of Erfurt. The total number concentration was governed by ultra-fine particles (o0.1 mm) (81% in 1993 and 90% in 1999) and 0.1–0.5 mm size fraction dominates total mass concentration (approximately 80%). While the mass concentration of fine particles (PM2.5) decreased from 39 to 19 mgm 3 , the geometric means of total number concentration showed constant concentration (13.3  10 3 cm 3 in 1993 and 13.3  10 3 cm 3 in 1999, p ¼ 0:975) and the geometric means of number concentration of ultra-fine particles (UP) between 10 and 30 nm increased from 5.9  10 3 to 8.2  10 3 cm 3 from 1993 to 1999 (p ¼ 0:016). The temporal changes of number and mass concentrations in the three communities are similar. The clear shift to smaller particle sizes within this six years period was caused by changes of the most prominent sources, traffic and domestic heating, since formerly dominating industries in Bitterfeld and Hettstedt had vanished grossly. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Ambient aerosol; Particle number concentration; Particle mass concentration; Aerosol spectrometer; Ultra-fine particles 1. Introduction Emissions of air pollutants in the densely populated industrial areas of the state of Sachsen-Anhalt in former East Germany prior to 1990 led to extreme concentra- tions of sulfur dioxide (SO 2 ), total suspended particles (TSP) and other airborne pollutants (Umweltbunde- samt, 1993). After re-unification in 1990 the decrease in industrial production, the reorganization and shut down of highly polluting industrial plants, as well as new legal regulations regarding emissions led to distinct decreases of pollutant emissions in the new states of Germany (Umweltbundesamt, 1993). The conversion of domestic heating systems from sulfur-rich surface coal to modern gas and oil affected local air pollution conditions favorably. In parallel the car fleet was renewed from old cars built in the eighties either in East or West Germany to modern cars utilizing western emission *Corresponding author. Tel.: +49-89-3187-4150; fax: +49- 89-3187-3380. E-mail address: joachim.heinrich@gsf.de (J. Heinrich). 1352-2310/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII:S1352-2310(01)00229-1