Variation in characteristics of ambient particulate matter at eight locations in the Netherlands – The RAPTES project
Highlights
► We successfully identified and characterized real-world situations with very different PM characteristics. ► Underground train station had the highest concentrations of almost every PM characteristic. ► Correlations between PM characteristics were low enough to investigate their independent health effects.
Introduction
In recent years numerous epidemiological studies have shown health effects related to short- and long-term exposure to elevated levels of ambient particulate matter (PM) (Brunekreef and Holgate, 2002, Pope and Dockery, 2006). These observations are supported by findings from controlled human exposure studies, animal toxicology and mechanistic in vitro studies (Maier et al., 2008, Lippmann and Chen, 2009).
Apart from regulated PM10 and PM2.5 mass concentrations, only a small number of PM characteristics are measured. Health effects have been mostly associated with the PM mass concentration and in few studies with specific PM characteristics such as number concentration, surface area, elemental and chemical composition, or oxidative potential (WHO, 2007, Brunekreef, 2010). Additionally, in epidemiological studies high correlations are typically present between the constituents (particulate as well as gaseous) of the air pollution mixture, which makes it difficult to disentangle their independent effects on human health (Brunekreef and Holgate, 2002).
A recent World Health Organization workshop (WHO, 2007) on the health relevance of PM from various sources suggested that future research should, among other things, (1) explore “the role of various characteristics of ultrafine, fine and coarse thoracic particles that might be responsible for health effects, (2) consider “the contributions of different emissions sources to population exposure”, (3) consider “other biological effects in the studies, beyond classically measured mortality or respiratory function and symptoms”, (4) ensure “that the exposure levels used in toxicological studies correspond to the components and levels of exposure experienced by populations and evaluated by epidemiological studies”, and (5) promote “an integrated study approach, combining detailed characterization of exposure, epidemiological observation of effects in populations and toxicological or clinical evaluation of the effects”.
We attempted to address these recommendations in the RAPTES project (Risk of Airborne Particles: a Toxicological–Epidemiological hybrid Study). The overarching aim of RAPTES was to combine real-world exposure conditions with an experimental exposure design so that health effects could be associated with specific ambient PM characteristics. In order to achieve this, we performed an extensive exposure assessment and characterization of physical, chemical and oxidative properties of PM at sites which were selected to provide high contrast and low correlation between PM characteristics and between contributing sources. At selected sites health effects were investigated in a panel of volunteers. PM samples were also collected for in vivo and in vitro experiments to investigate the mechanisms behind the health effects.
In this paper we present a detailed characterization of air pollution at the selected sites focusing on particulate air pollution and the contrast and correlations between its physical and chemical characteristics. The associated health impacts will be presented in subsequent publications.
Section snippets
Sampling site selection
We selected sites anticipated to provide a large contrast in exposure to specific characteristics of PM as well as a low correlation between PM characteristics, based upon previous studies of specific sources. The characteristics we took into account were mass concentration of particles less than 10 μm and less than 2.5 μm in aerodynamic diameter (PM10 and PM2.5, respectively) as well as the mass concentration of coarse PM fraction (PM2.5−10), particle number concentration (PNC) as a proxy for
Results
We completed 60 visits in total. Data from one day at the truck traffic site were not included in the analysis, due to a sudden weather change which interrupted the sampling. Data from four other sampling days were not included as they did not meet the specific criteria, particularly main wind direction from the source to the site. In total, 55 days were included in the analysis (Table 1).
Distribution of air pollution concentrations across the sampling locations is presented in Table 2 and
Discussion
We performed a detailed characterization of particulate air pollution at eight locations in the Netherlands. We found significant differences in PM characteristics between the sampling sites in a complex set of air pollution concentration measurements. The underground train station, compared to each outdoor location, had substantially higher concentrations of almost every PM characteristic, including PM mass, EC and trace metal concentrations, while the traffic sites had the highest particle
Conclusions
We conclude that we were able to successfully identify and characterize real-world situations with very different particle characteristics. High contrast and low correlations between PM characteristics, as well as consistency of these differences across sampling campaigns, provide a good basis for identifying health relevant PM characteristics in the upcoming analysis.
Acknowledgments
We would like to thank John Boere, Paul Fokkens, Daan Leseman (RIVM), Kees Meliefste (IRAS) and students: Lise van den Burg, Veerle Huijgen, Maartje Kleintjes, Marja Meijerink and Jet Musters for their help with data collection.
The RAPTES project was funded by the RIVM Strategic Research Program (SOR).
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