Determinants of ultrafine particle exposures in transportation environments: findings of an 8-month survey conducted in Montréal, Canada

Abstract

An 8-month sampling campaign was conducted in Montre´al, Canada to explore determinants of ultrafine particle (UFP) exposures in transportation environments and to develop models to predict such exposures. Between April and November 2006, UFP (0.02-1 mm) count exposure data were collected for one researcher during 80 morning and evening commutes including a 0.5-km walk, a 3-km bus ride, and a 26-km automobile ride in each direction. Ambient temperature, relative humidity, precipitation, and wind speed/direction data were collected for each transit period and the positions of bus and automobile windows were recorded. Mixing heights were also estimated. Morning UFP exposures were significantly greater than those in the evening, with the highest levels observed in the automobile and the lowest while walking. Wind speed and mixing height were highly correlated, and as a result only wind speed was considered in multivariable models owing to the accessibility of quantitative hourly monitoring data. In these models, each 101C increase in morning temperature was associated with decreases of 14,560/cm 3 (95% CI ¼ 11,111 to 18,020), 8160/cm 3 (95% CI ¼ 5060 to 11,260), and 11,310/ cm 3 (95% CI ¼ 6820 to 15,810) for UFP exposures in walk, bus, and automobile environments, respectively. Likewise, each 10-km/h increase in morning wind speed corresponded to decreases of 8252/cm 3 (95% CI ¼ 5130 to 11,360), 6210/cm 3 (95% CI ¼ 3420 to 9000), and 6350/cm 3 (95% CI ¼ 2440 to 10,260) for UFP exposures in walk, bus, and automobile environments, respectively. Similar trends were observed in the evening hours. In an evaluation of model performance, moderate correlations were observed between measured and predicted UFP exposures on new bus (r ¼ 0.65) and automobile (r ¼ 0.77) routes. Further research is required to incorporate variables such as traffic density and vehicle ventilation settings into the models presented.

Personal exposure to ultrafine particles

“…Both background outdoor concentrations (9000-10,000 particles/cm 3 ) and vehicle interior concentrations (29,000-34,000 particles/cm 3 ) were very similar on the East and West Coast highways. These readings are quite similar to those noted in an 8-month study in Montreal: 38,000 particles/cm 3 in the evening, 31,000 particles/cm 3 in the morning (Weichenthal et al, 2008). They are lower than those reported on Los Angeles freeways by Westerdahl et al (2005) and Zhu et al (2008), which probably is because of the exceptionally high volume of heavy duty diesel-powered trucks on the Los Angeles freeways selected for their studies (Zhu, 2008).…”

Characterizing the spatial distribution of ambient ultrafine particles in Toronto, Canada: A land use regression model

“…This decision was based on existing evidence suggesting that ambient temperature is an important determinant of day-to-day changes in ambient UFPs (Alm et al, 1999;Kaur and Nieuwenhuijsen, 2009;Weichenthal et al, 2008Weichenthal et al, , 2014. Regardless, this may be considered a limitation as previous studies have relied on fixed-site data for UFPs (Abernethy et al, 2013;Hoek et al, 2011) or NO x (Rivera et al, 2012) to adjust for temporal variability and we cannot rule out a residual impact of temporal variation on our results.…”

“…Previous studies have used correction factors derived from fixed site monitoring data for UFPs (Abernethy et al, 2013;Hoek et al, 2011) or NO x (Rivera et al, 2012) to adjust for temporal variations between samples collected at different times. Since fixed-site UFP data were not available in Toronto, we used ambient temperature to adjust for temporal variability between sampling periods as temperature is known to be an important determinant of day-to-day fluctuations in ambient UFPs (Alm et al, 1999;Kaur and Nieuwenhuijsen, 2009;Weichenthal et al, 2008Weichenthal et al, , 2014. Specifically, each road segment was assigned a value for mean ambient temperature using real-time data (1-second resolution) collected from vehicle rooftop monitors (HOBO Datalogger) at the same time as UFP measurements.…”

Modeling Spatial Patterns of Traffic-Related Air Pollutants in Complex Urban Terrain

“…Recent mobile-monitoring studies have reinforced these findings. A study conducted in Montreal, Canada, found UFP concentrations measured in various transportation microenvironments to be inversely associated with temperature and wind speed (Weichenthal et al 2008) but did not investigate the impacts of traffic. Another study conducted in Beijing, China, found a strong impact of traffic on UFP concentrations but did not formally incorporate meteorological parameters (Westerdahl et al 2009).…”