Small-scale spatial variability of particle concentrations and traffic levels in Montreal: a pilot study

doi:10.1016/j.scitotenv.2004.07.013

Science of The Total Environment

Volume 338, Issue 3, 15 February 2005, Pages 243-251

https://doi.org/10.1016/j.scitotenv.2004.07.013 Get rights and content

Abstract

Little is known about the particulate exposure of populations living along major urban roads. The objective of this pilot study was to explore the small-scale spatial and temporal variability of the absorption coefficient of PM2.5 filters, as a surrogate for elemental carbon, in relation to levels of PM2.5, at residential sites with varying traffic densities in a large Canadian city. Concurrent 24-h measurements were performed at four residential sites during 7 weeks. A gradient existed across all four sites for the absorption coefficient of the filters (and NO₂ levels). In contrast, the levels of PM2.5 were quite similar at all sites. The difference in the filter absorption coefficient of PM2.5 filters, between an urban background and a residential traffic site (with about 30 000 vehicles/day), expressed as a percentage of the background site, was 40%. These results indicate that spatial variability in PM2.5 absorption coefficient can be observed with traffic intensity on a small scale within a North American city and suggests that regression modelling approaches similar to those used in European studies could be used to estimate exposure of the general population to traffic-related particles on a local scale in North America.

Introduction

Time series studies strongly support an association between ambient particle levels and rates of hospitalisations and mortality for cardio-respiratory illnesses. National and regional Canadian inventories show that emissions from traffic contribute appreciably to the mass of ambient particles, especially in urban areas (Environment Canada-Health Canada, EC-HC, 2000).

Evidence exists to suggest that those living along major roads and exposed to traffic-related pollutants may experience higher rates of hospitalisation for respiratory problems (e.g. Edwards et al., 1994, Buckeridge et al., 2002) and may be at higher risk of non-traumatic mortality due to exposure to traffic emissions (Roemer and van Wijnen, 2001, Hoek et al., 2002a). Little is known about the spatial variability of particle exposure of populations living in urban areas. Most epidemiological studies have used crude indicators such as distance to major roads to represent exposure to traffic emissions.

There is a lack of information on the exposure of the general population to particles and their components on a small scale within urban regions in North America. Regional variations in the levels of PM2.5 (particulate matter with aerodynamic diameter of less than 2.5 μm) of urban, suburban and rural areas have been found (EC-HC, 2000). However, levels of PM2.5 have been reported to be quite uniform on a local scale. Primary particles (diameter less than 0.1 μm), which contribute little to the mass, and large particles (more than 10 μm) are expected to have a larger spatial variability than particles in the accumulation mode (0.1–1 μm) (for review see Monn, 2001). Elemental carbon has been used to characterise exposure to particulate emissions due to traffic (e.g. Brauer et al., 2002, Hoek et al., 2002a, Hoek et al., 2002b). There is a strong correlation between measured elemental carbon and filter light absorption, so measures of filter light absorption have been used as a surrogate for elemental carbon levels (e.g. Kinney et al., 2000, Janssen et al., 2001, Rich, 2002).

Studies have shown a marked decreased in the filter light absorption coefficient (Roorda-Knape et al., 1998) and in elemental carbon levels (Zhu et al., 2002) within the first 150 m from highways. It is unclear from these studies to what extent the levels measured in proximity to roads differ from background levels. Studies conducted in Europe show that the filter light absorption in close proximity to roads varies with traffic intensity while PM2.5 levels measured at the same locations varied to a smaller extent relative to distance from roads and traffic intensity (e.g. Janssen et al., 1997, Hoek et al., 2002b).

Recently, elemental carbon levels have also been shown to vary across a community heavily impacted by truck traffic in New York City (Lena et al., 2002). Apart from such hot spots, relatively little is known about the extent to which the levels of PM2.5 and elemental carbon levels vary within North American cities with traffic intensity on a local scale. The Multiple Air Toxics Exposure Study (MATES-II) has shown on a regional scale that traffic emissions contribute to regional variations in elemental carbon levels in California (http://www.aqmd.gov/matesiidf/matestoc.htm). Gaseous pollutants such as carbon monoxide and nitrogen dioxide are known to vary with traffic intensity on a small scale (e.g. Roorda-Knape et al., 1998, Maynard and Waller, 1999, Rijnders et al., 2001).

The objective of the current study was to explore ambient concentrations of traffic-related airborne particles at residential sites in a large Canadian city. Specifically, the small-scale spatial and temporal variability of the absorption coefficient of PM2.5 filters, as a surrogate for elemental carbon, was examined in relation to levels of PM2.5 at sites with varying traffic densities.

Section snippets

Design

Four residential sites in the City of Montreal were selected based on traffic levels for monitoring of the small-scale spatial variability in air pollutants. PM2.5, absorption coefficient of PM2.5 filters and nitrogen dioxide (NO₂) concentrations were measured as indicators of traffic emissions. Concurrent 24-h sampling for PM2.5 took place over a 7-week period between May 6 and June 28, during a 4-week consecutive sampling period followed by a 3-week period. This time period was chosen when

Study description

A total of 155 out of 174 PM2.5 filters were successfully collected (91%), including 17 duplicates, and six NAPS collocated samples. The remaining filters were lost, mainly due to of pump failures. The number of collocated filters was also less than planned because two filters were lost due to technical problems, one from pump failure of the collocated Harvard Impactor, one through coordination problems with the city of Montreal. One filter collected by the Partisol of the city of Montreal was

Discussion

In the present study, concurrent 24-h measurements of the levels of PM2.5, of the absorption coefficient of the PM2.5 filters and of NO₂ levels were performed at four residential sites in the City of Montreal with differing levels of traffic intensity. A gradient existed across all four sites for both the absorption coefficient of the filters and NO₂ levels (Table 2), reflecting the importance of local traffic sources. The levels of PM2.5 were quite similar at all sites, as anticipated given

Acknowledgements

This project was funded by the Quebec Ministry of Health (85%) and by Health Canada (15%). We thank the city of Montreal for conducting traffic counts at our sites of measurements and the Montreal Island Direction of the Quebec Ministry of Transportation for providing traffic counts on the expressway. We also thank the members of the community involved and Sophie Goudreau and Simon Lajeunesse for their technical assistance.

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Small-scale spatial variability of particle concentrations and traffic levels in Montreal: a pilot study

Abstract

Introduction

Section snippets

Design

Study description

Discussion

Acknowledgements

Sci. Total Environ.

Lancet

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Air pollution from traffic and the development of respiratory infections and asthmatic and allergic symptoms in children

Am. J. Respir. Crit. Care Med.

Effect of motor vehicle emissions on respiratory health in an urban area

Environ. Health Perspect.

Comparison between different traffic-related particle indicators: elemental carbon (EC), PM(2.5) mass, and absorbance

J. Expo. Anal. Environ. Epidemiol.

Hospital admissions for asthma in preschool children: relationship to major roads in Birmingham, United Kingdom

Arch. Environ. Health