Indoor air measurement campaign in Helsinki, Finland 1999 - the effect of outdoor air pollution on indoor air

Wintertime indoor and outdoor particle size distributions were studied in a n office building near Helsinki downtown by measuring the particle size dis tributions with two similar differential mobility particle sizer systems (D MPS). Measurements were made simultaneously at two places; on the rooftop o f a building (30 m above the ground level) in front of a ventilation system corresponding to outdoor concentration, and an office room (first floor). The ventilation rate was also continuously monitored. Indoor particle conce ntrations were observed to vary from 500 to 10(4) cm(-3) with a high depend ence on the outdoor concentrations. This indicates that in this scenario, i ndoor particles are mainly of outdoor origin. Effects of ventilation rates on indoor air particle concentrations and several inorganic gases were stud ied. We found that ventilation had a strong influence on indoor particle an d gas concentrations. I/O (indoor/outdoor) ratio in different in different particle size classes. (C) 2001 Elsevier Science Ltd. All rights reserved.