Indoor Exchange Rates and Penetration From Outdoors in an Instrumented Terraced House (Townhouse) Using Gas Tracers: Implications for Particles and Gases Indoors

Air exchange rate is a key determinant of indoor air quality which is highly variable within the rooms of a naturally ventilated terraced house (townhouse). Window opening can increase the air exchange rate, but internal door opening between rooms inside decreases the rate. Inert perfluorocarbon gas-phase tracers demonstrated flow within the house, and the penetration of tracers released outside into the house showed a strong dependence on wind speed and wind direction. Between experiments, it was found that the tracer could be detected within certain parts of the house weeks after the initial release, with implications for pollutants and their impact on the indoor environment. A limited number of reactive tracer experiments suggested an upper limit for indoor [OH]~1 × 10⁵ molecule cm^-3 with up to 0.5 ppt of [NO₃] estimated, leading to an estimated indoor lifetime for d5 isoprene of many hours. Ultrafine particulate matter generated in the kitchen travels throughout the house, and the persistence of elevated aerosol concentrations is seen even in well-ventilated rooms, with implications for particle exposure in the evening and during the night.