The protective effect of houses on air-polution episodes

The time-integrated in- and outdoor air pollution concentration will differ during a pollution episoe. The ratio of the former to the latter has been found for 17 Danish dwellings. In 15 of them a separate ratio was found for each room with the inner doors closed. In the last 2 dwellings the inner doors were left open, and for all 17 dwellings the outer doors and windows were kept shut during the measurements. It has been shown to be convenient to classify the pollutants into three categories: 1. non-reactive gases (e.g. nobel gases), 2. non-reactive particles, 3. reactive matter (e.g. elementary iodine). The indoor/outdoor ratio described above has been found for non-reactive gases by using SF6 as a tracer. For non-reactive particles the relationship has been found by means of 7Be-marked particles, created by spallation in the atmosphere, and 103Ru-marked particles originating from Chinese nuclear bomb tests in the atmosphere. In the present investigation the relationship for reactive matter has not been measured. However, from the relevant literature and a comparison of the deposition and filtering mechanism for non-reactive particles and reactive matter a maximum value for the indoor/outdoor relationship for reactive matter has been found. The relation between the outdoor/indoor ratio and the exchange velosity has also been investigated and an equation describing it has been established. The effect of operating a vacuum cleaner during the pollution episode and airing shortly afterward was also investigated. It is found that staying indoors in a normal living-room with closed windows and doors will reduce the aerosol inhalation dose by a factor of about 3. Operating a vacuum cleaner while staying indoors will increase this reduction factor to about 9. Airing one hour after the passage of a plume of three hours duration will raise these two factors to 6 and 12, respectively. The only way to obtain a reduction in inhalation dose from non-depositing gases is by controlled airing. Under the above-mentioned condition, airing will reduce the inhalation dose for non-depositing gases by a factor of about 2. (author)