Spatial and temporal variations of particulate matter concentrations in multifamily apartment buildings

• Fifty apartments in ten multifamily buildings were investigated.
• Indoor PM was characterized by decay rate, I/O ratios and background concentrations.
• PM indicators varied greatly among the investigated buildings and apartments.
• Indoor PM were largely affected by increased wintertime outdoor pollution.

We report a comprehensive assessment of PM concentrations and its variations in multifamily apartment buildings. Fifty apartments in ten multifamily buildings were investigated during heating seasons of 2011 and 2012 in Kaunas city, Lithuania. PM concentration and size distribution measurements were performed using the optical particle counters indoors and outdoors. Usually mean 24-h indoor PM concentrations were lower (median 7.8 μg/m3 for PM2.5) than outdoor concentrations (median 16.9 μg/m3 for PM2.5) of corresponding location, and I/O ratios of PM2.5 were lower (0.70) than that of PM10 (0.98). Night time levels, representing background indoor exposure to PM, were equal to 5.0 (PM2.5) and 6.7 μg/m3 (PM10), respectively. Particle deposition rates were determined by regression fitting of the measured PM2.5 concentration decay curves, with the median equal to 0.32 h−1. The data have been discussed aiming to characterize indoor PM sources and select the most representative indicator(s) for an assessment of the effects of energy saving refurbishment on indoor air quality. We found that a combination of several indicators allowed an adequate characterization of indoor PM sources and can be used in the subsequent assessment.