Residential indoor and outdoor ultrafine particles in Windsor, Ontario
Highlights
► Residential indoor and outdoor ultrafine particles were measured in Windsor, Ontario. ► Outdoor UFPs were more spatially variable than concurrently measured PM2.5. ► Outdoor levels generally exceeded indoor levels but indoor peaks were larger. ► Infiltration rates were variable across homes; seasonal medians ranged from 16 to 26%. ► Median deposition rates ranged from 0.6 to 0.8 h−1 across the 3 sampling sessions.
Introduction
Ultrafine particles (UFP) have diameters < 100 nm. Their small size allows them entry into all parts of the lung including the alveoli as well as other human cells of various tissue types. The main outdoor sources are auto exhaust and atmospheric reactions (Kittelson, 1998, Gaydos et al., 2005). Indoor sources include cooking (Dennekamp et al., 2001, Wallace et al., 2008), indoor chemical reactions of ozone and terpenes (as found in various cleaning products) (Singer et al., 2006), candles and incense burning (Klepeis et al., 2003) and electric motors (Szymczak et al., 2007). Animal and human studies have shown effects on various health endpoints, including oxidative damage to DNA repair mechanisms (Bräuner et al., 2007) and total and cardio-respiratory mortality (Stölzel et al., 2007). In assessing human exposure to outdoor-generated UFPs while indoors, it is important to know how well a central site monitor captures the temporal and spatial variability of ambient UFP concentrations and to understand the magnitude and variability of infiltration of ambient UFPs into homes. Some studies of indoor and outdoor UFP concentrations have been published (e.g. Long et al., 2001); however, only a few have involved indoor and outdoor measurements at multiple homes (He et al., 2005, Puustinen et al., 2007, Weichenthal et al., 2007, de Hartog et al., 2010). Deposition rates are another important parameter in determining human exposure to particle, however, few residential measurements have been made for UFPs.
In 2005–06 a personal exposure study was carried out in Windsor, Ontario to assess levels of exposure to various air pollutants and to investigate the relationships between personal, indoor and outdoor levels. Windsor, a city of 216,500 residents (2006 census, City of Windsor, 2010) is across the Detroit River from Detroit, Michigan. It is the home of the major Canadian automotive manufacturers and related industries and there is significant diesel truck traffic to and from the U.S. over the Ambassador Bridge. Previous publications have reported the study methods (Wheeler et al., in press-a), quality assurance results for the continuous measurements (including UFP) (Wallace et al., 2010) and summary findings on the particle-related continuous measurements including PM2.5, UFP, and black carbon (Wheeler et al., in press-b). This manuscript provides a more in-depth analysis of the indoor and outdoor UFP continuous measurements, including analysis of temporal and spatial variability, estimation of the UFP infiltration factors, deposition rates and the ambient and non-ambient components of indoor UFPs.
Section snippets
Methods
In summer 2005 (Jul–Aug), indoor and outdoor UFP measurements were obtained from 45 homes of non-smoking adults in Windsor, ON. In winter 2006 measurements were taken in 47 homes of asthmatic children (10–13 y). The following summer, measurements were taken in 46 homes; 44 of which had participated in the winter 2006 season. In each of the 3 sampling sessions, which occurred over an 8 week period, 6 homes were sampled concurrently each week, generally from Monday evening to late afternoon on
Home characteristics
Participant’s homes were located throughout Windsor; the median distance between pairs of homes was 6.4 km in 2005 and 5.3 km in 2006 (ranging from 0.2 to 18.8 km). Homes were primarily single-family, detached dwellings with non-smoking occupants. The majority of the 94 homes with measurements used in this analysis relied on forced air furnaces (96%) for heating, fuelled predominantly by natural gas. More than half of the homes reported a furnace-installed air cleaner (premium filter, HEPA filter
Conclusions
This is one of the first studies that has estimated UFP infiltration and deposition rates for a large number of homes. Based on censored indoor/outdoor ratios, the median weekly UFP infiltration factors were 0.16, 0.26 and 0.21 in the three sampling sessions, however values ranged from 0.04 to 0.86 across individual homes. For more than 65% of homes, indoor-generated UFPs provided more of the total indoor UFP concentration than infiltrated ambient UFPs. Mean deposition rates across the three
Acknowledgements
Funding for this study was provided by Health Canada under the Border Air Quality Strategy.
The authors would like to thank the participants of the study and their families and the field technicians and other staff involved in carrying out the project. Thanks to Stan Judek for implementing the recursive mass balance model using Excel Solver. Thanks also to Scott Weichenthal, Cheryl Khoury, Roger Sutcliffe,Dave Stieb and two anonymous reviewers for their helpful comments.
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