Saturday, July 09, 2005

Control of Fine Particle Exposures

The Dodger encountered Indoor Air, a journal previously unknown, while browsing medline for more grist for the fine particle mill.

The paper finds that a 27% reduction in fine particle exposure can be achieved by adding filtration for forced air ventilation systems.

Finland by building code requires particle filtration in recirculating ventilation systems, both residential and occupational buildings. This paper is detailed, and refers to previous publications, so the Dodger couldn't find a description of the filtration in the ventilation systems in the buildings studied. [The Dodger will go back through this series, because it includes a lot of data on personal vs. community exposure measurements. That's for another post.]

Commonly used filters for ventilation vary widely in efficiency, from 25 to 67%. It would be surprising if there were any 95% filters in this sample, although Finland can be surprising. The Dodger suggests that much of the collection efficiency against fine particles in these systems results from impaction of drawing air through a more complicated path rather than the filter itself.

In addition, fine particles preferentially penetrate filters. Minimum filter efficiency is at 0.3 microns. PM2.5 is a standard measure because of instrumental considerations, but the bulk of the mass in PM 2.5 is really PM 1.0. Particle numbers will bulk up at lower diameters. Therefore, it is unlikely that the full potential for improved filtration has been found.

Measuring real world reductions is needed to account for air infiltration outside of the ventilation system. An obvious next step would be designing or modifying a commercially available or viable building system with the aim of capturing in the PM 1.0 range, putting it into a real residential building, and measureing the result.

Indoor Air. 2005 Aug;15(4):246-56.

Reduction potential of urban PM mortality risk using modern ventilation systems in buildings.

Hanninen OO, Palonen J, Tuomisto JT, Yli-Tuomi T, Seppanen O, Jantunen MJ.
KTL, Centre for Environmental Health Risk Analysis, Kuopio, Finland.

While waiting for technological breakthroughs in emission controls, the current work assesses the exposure reductions achievable by a complementary means: efficient filtration of supply air in buildings. For this purpose infiltration factors for buildings of different ages are quantified using Exposures of Adult Urban Populations in Europe Study (EXPOLIS) measurements of indoor and outdoor concentrations in a population-based probability sample of residential and occupational buildings in Helsinki, Finland. These ... compare exposures in the current scenario with an alternative scenario, where the distribution of ambient PM(2.5) infiltration factors in all residential and occupational buildings are assumed to be similar to the subset of existing occupational buildings using supply air filters. In the alternative [filtration equipped] scenario exposures to ambient PM(2.5) were reduced by 27%. ... The estimated exposure reductions suggest that correctly defined building codes may reduce annual premature mortality by hundreds in Finland and by tens of thousands in the developed world altogether.

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