Spatial variability of trace elements and sources for improved exposure assessment in Barcelona
Introduction
Exposure to air pollution has adverse health effects, including increased mortality and morbidity (Cohen et al., 2005, Perez et al., 2009, Zanobetti and Schwartz, 2009). Most of the health studies are based on ambient measurements taken at a single sampling point in a city, but the pollutants concentrations may vary across the city (Hoek et al., 2002, Minguillón et al., 2012b, Mangia et al., 2013). Therefore, accounting of the spatial variability within a city would allow an improved exposure assessment, which could have an important impact on the effect estimates (Setton et al., 2010, Kloog et al., 2013). This variability may differ between cites due to differences in urban structure, vehicle fleet composition and fuel types. Moreover, current estimates of the European health impact of ambient particulate matter (PM) are primarily based on exposure–response relationships established in studies from North America. Hence the need of studies on recent and current exposures in Europe using refined exposure assessment tools is clear.
The ESCAPE project (European Study of Cohorts for Air Pollution Effects, www.escapeproject.eu) aims to investigate long-term effects on human health of exposure to air pollution in Europe. The overall strategy is to efficiently utilise health and confounder data from existing European cohort studies by adding air pollution exposure assessment, focussing on spatial variation of long-term average ambient PM, PM composition and NOx concentrations in a number of European cities.
The present study focuses on the city of Barcelona, as one of these cities. Barcelona city has a high traffic density in comparison to other European cities, a large proportion of diesel vehicles, and a specific geography and city design, with abundant semi-tall buildings and relatively narrow streets leading to the known street canyon effect (Mirzaei and Haghighat, 2012). Several studies on the air quality of Barcelona, including PM source apportionment, have been carried out (Querol et al., 2001, Amato et al., 2009a, Perez et al., 2009, Pérez et al., 2010). Nevertheless, they do not cover the spatial variation of ambient pollutants and source contributions. Knowing the spatial distribution of the contribution of different sources of ambient PM and not only the ambient pollutants concentrations may be a useful tool to identify the location of the sources and to better understand how the emissions are transported through the city. Therefore, the present study aims at evaluating the pollution by particulate matter in Barcelona and its chemical composition in terms of spatial and temporal variability, and at identifying the main PM sources and studying the spatial variation of their contributions.
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Sampling sites, schedule and instrumentation
There is a well-defined methodology followed during the ESCAPE study regardless of the specific area of study (www.escapeproject.eu/manuals/) and detailed methods can be found elsewhere (Eeftens et al., 2012). For the exposure assessment, 20 sites were selected in Barcelona, together with a reference site (Fig. 1, Table S1). From those, 6 sites were classified as urban background (UB), 13 sites were traffic sites (TR), 1 site was considered rural background (RB) and the reference site was
Average concentrations and seasonal variability
Average concentrations (without temporal adjustment) of the analysed elements are shown in Fig. 2, together with the usual concentrations measured in Spanish urban areas (Querol et al., 2008). Given that the sampling was carried out at different times of the year, seasonal averages were calculated to identify possible season-dependent variations. The concentrations of most of the elements fall within the usual range in PM10 and in PM2.5. To further identify the seasonal variation, the data was
Conclusions
The concentrations of most of the elements measured across Barcelona fell within the usual urban Spanish range in PM10 and in PM2.5. Most of the elements were measured in higher concentrations during the warm period, some of them attributed to mineral matter and some other attributed to fueloil combustion emissions. The higher S concentrations in summer may be due to the sulphate temperature-dependent particle–gas equilibrium and speed of formation. The SiO2/Al2O3 ratios were homogeneous across
Acknowledgements
This work was funded by the ESCAPE (European Study of Cohorts for Air Pollution Effects, grant agreement no 211250) and TRANSPHORM (Transport related Air Pollution and Health impacts – Integrated Methodologies for Assessing Particulate Matter, grant agreement no 243406) projects under the European Union's Seventh Framework Programme, and the Generalitat de Catalunya 2009 SGR8. M.C. Minguillón was partially funded by the JAE-Doc CSIC program, co-funded by the European Social Fund (ESF).
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