Hans Orru^1,, Alo Mikola², Madis Upan², Teet-Andrus Koiv²

As people spend up to 90% of their time indoors, indoor air pollution plays a crucial role in their air pollution exposure. Particulate matter (PM₁₀) and fine particles (PM_2.5) were measured with optical particle counters during three days in summer and winter inside and outside four homes with different ventilation, heating systems and lifestyles in Tallinn. It appeared that during the period outdoor concentrations of PM₁₀ were relatively low, even though three of the measuring sites were situated near busy streets (15.8 and 25.9 μg/m³ as summer and winter period average). At the same time the mean indoor PM₁₀ values were 15.0 μg/m³ in summer and 22.2 μg/m³ in winter and up to 94% of the particles were fine particles. The average I/O ratios varied from 0.6 to 1.2 depending on the location and season. The highest indoor concentrations appeared during cooking; however, these peaks did not appear in a flat with a portable air filter. Moreover, residential heating affected both indoor and outdoor air quality causing significantly higher levels in winter and there was also some effect of outdoor fires in summer. Mechanical ventilation somewhat improved the air quality, but during high indoor emission episodes (cooking) it was not sufficient.

particulate matter, indoor air pollution, ventilation, heating