Spatial and indoor/outdoor gradients in urban concentrations of ultrafine particles and PM2.5 mass and chemical components

Stefano Zauli Sajani*, Isabella Ricciardelli, Arianna Trentini, Dimitri Bacco, Claudio Maccone, Silvia Castellazzi, Paolo Lauriola, Vanes Poluzzi, Roy M. Harrison

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)
371 Downloads (Pure)


In order to investigate relationships between outdoor air pollution and concentrations indoors, a novel design of experiment has been conducted at two sites, one heavily trafficked and the other residential. The novel design aspect involves the introduction of air directly to the centre of an unoccupied room by use of a fan and duct giving a controlled air exchange rate and allowing an evaluation of particle losses purely due to uptake on indoor surfaces without the losses during penetration of the building envelope which affect most measurement programmes. The rooms were unoccupied and free of indoor sources, and consequently reductions in particle concentration were due to deposition processes within the room alone. Measurements were made of indoor and outdoor concentrations of PM2.5, major chemical components and particle number size distributions. Despite the absence of penetration losses, indoor to outdoor ratios were very similar to those in other studies showing that deposition to indoor surfaces is likely to be the major loss process for indoor air. The results demonstrated a dramatic loss of nitrate in the indoor atmosphere as well as a selective loss of particles in the size range below 50nm, in comparison to coarser particles. Depletion of indoor particles was greater during a period of cold weather with higher outdoor concentrations probably due to an enhancement of semi-volatile materials in the outdoor particulate matter. Indoor/outdoor ratios for PM2.5 were generally higher at the trafficked site than the residential site, but for particle number were generally lower, reflecting the different chemical composition and size distributions of particles at the two sites.

Original languageEnglish
Pages (from-to)307-320
Number of pages14
JournalAtmospheric Environment
Early online date29 Dec 2014
Publication statusPublished - 1 Feb 2015


  • Deposition
  • Indoor-outdoor air
  • Nanoparticles
  • PM

ASJC Scopus subject areas

  • Atmospheric Science
  • Environmental Science(all)


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