Mihalis Lazaridis1, Kostas Eleftheriadis2, Vladia Ždímal3, Jaroslav Schwarz3, Zdenek Wagner3, Jakub Ondráček3, Yannis Drossinos4, Thodoros Glytsos 1, Sterios Vratolis2, Kjetil Torseth5, Pavel Moravec3, Tareq Hussein6,7, Jiri Smolík3

  • 1 School of Environmental Engineering, Technical University of Crete, Chania 73100, Greece
  • 2 Institute of Nuclear Technology & Radiation Protection, N.C.S.R. “Demokritos”, 15310 Ag. Paraskevi, Attiki, Greece
  • 3 Institute of Chemical Process Fundamentals, Laboratory of Aerosol Chemistry and Physics, Rozvojová 135, CZ-16502 Praha 6, Prague, Czech Republic
  • 4 European Commission, Joint Research Centre, I-21020 Ispra (Va), Italy
  • 5 Norwegian Institute for Air Research (NILU), Instituttviein 18, N-2020 Kjeller, Norway
  • 6 The University of Jordan, Department of Physics, Amman, 11942, Jordan
  • 7 University of Helsinki, Division of Atmospheric Sciences, FI-00014 UHEL, Helsinki, Finland

Received: July 8, 2015
Revised: July 6, 2016
Accepted: August 8, 2016
Download Citation: ||https://doi.org/10.4209/aaqr.2015.04.0267  

Cite this article:
Lazaridis, M., Eleftheriadis, K., Ždímal, V., Schwarz, J., Wagner, Z., Ondráček, J., Drossinos, Y., Glytsos, T., Vratolis, S., Torseth, K., Moravec, P., Hussein, T. and Smolík, J. (2017). Number Concentrations and Modal Structure of Indoor/Outdoor Fine Particles in Four European Cities. Aerosol Air Qual. Res. 17: 131-146. https://doi.org/10.4209/aaqr.2015.04.0267


  • Indoor/outdoor measurements have been performed in four European cities.
  • The characteristics of indoor and outdoor size distributions were determined.
  • Indoor activities affected the characteristics of the indoor modal structure.
  • Indoor activities resulted in the strong presence of Aitken mode particles.



Indoor/outdoor aerosol size distribution was measured in four European cities (Oslo–Norway, Prague–Czech Republic, Milan–Italy and Athens–Greece) during 2002 in order to examine the differences in the characteristics of the indoor/outdoor modal structure and to evaluate the effect of indoor sources to the aerosol size distributions. All the measurement sites were naturally ventilated and were occupied during the campaigns by permanent residents or for certain time periods by the technical staff responsible for the instrumentation. Outdoor particle number (PN) concentrations presented the higher values in Milan and Athens (median values 1.4 × 104 # cm–3 and 2.9 × 104 # cm–3 respectively) as a result of elevated outdoor emissions and led to correspondingly higher indoor values compared to Oslo and Prague. In absence of indoor activities, the indoor concentrations followed the fluctuations of the outdoor concentrations in all the measurement sites. Indoor activities (cooking, smoking, etc.) resulted in elevated indoor PN concentrations (maximum values ranging between 1.7 × 105 # cm–3 and 3.2 × 105 # cm–3) and to I/O ratios higher than one. The I/O ratios were size dependant and for periods without indoor activities, they presented the lowest values for particles < 50 nm (0.51 ± 0.15) and the ratios increased with fine particle size (0.79 ± 0.12 for particles between 100–200 nm). The analysis of the modal structure showed that the indoor aerosol size distribution characteristics differ from the outdoors under the effect of indoor sources. The percentage of unimodal size distributions increased during indoor emissions, compared to periods without indoor sources, along with the number concentration of Aitken mode particles, indicating emissions in specific size ranges according to the type of the indoor source.

Keywords: Indoor/Outdoor aerosol; I/O ratio; Modal structure; Indoor sources

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