Indoor and outdoor sources and infiltration processes of PM1 and black carbon in an urban environment

Ambient air emissions of sub-micron particles infiltrate into indoor environments and play a major role in indoor air quality. Discriminating between particles of indoor vs. outdoor origin is therefore essential when assessing indoor air pollutant levels and characteristics. Outdoor/indoor relationships of traffic-derived nanoscaled particulates (PM1 and black carbon) were determined in a typical Mediterranean environment. Results evidenced the major impact of outdoor vehicular traffic emissions on indoor particulates: despite windows remaining closed at all times, 70% of indoor BC and 73% of indoor PM1 originated from outdoor emissions. This was probably due to due to inadequate insulation of the building. Outdoor/indoor penetration ratios were relatively constant for BC (1.29 ± 0.08) but not for PM1 (1.95 ± 0.38), suggesting it is advisable to monitor the variability of penetration factors over time. Particle infiltration seemed to depend not only on physical barriers (building envelope, ventilation systems, etc.), but also on the physico-chemical properties of the particulates. Printing and photocopying contributed with 25–30% (546 ng m−3) of total indoor BC. Dust re-suspension by worker passage was the main indoor source of PM1 (15–20%, 1.1 μg m−3).

► We assess the impact of outdoor particle emissions on indoor air quality.
► We examine sub-micron particulates: PM1 and black carbon (BC).
► 70% of indoor BC and 73% of indoor PM1 originated from outdoor emissions.
► Outdoor/indoor penetration ratios vary with time and should be monitored.
► Printing/copying and dust re-suspension are the main indoor sources of BC and PM1.