Abstract
Abstract. The mass concentration, chemical composition and sources of quasi-ultrafine (quasi-UFP, PM0.25), accumulation (PM0.25–2.5) and coarse mode (PM2.5–10) particles were determined in indoor and outdoor air at 39 schools in Barcelona (Spain). Quasi-UFP mass concentrations measured (25.6 μg m−3 outdoors, 23.4 μg m−3 indoors) are significantly higher than those reported in other studies, and characterised by higher carbonaceous and mineral matter contents and a lower proportion of secondary inorganic ions. Results suggest that quasi-UFPs in Barcelona are affected by local sources in the schools, mainly human activity (e.g. organic material from textiles, etc., contributing 23–46% to total quasi-UFP mass) and playgrounds (in the form of mineral matter, contributing about 9% to the quasi-UFP mass). The particle size distribution patterns of toxicologically relevant metals and major aerosol components was characterised, displaying two modes for most elements and components, and one mode for inorganic salts (ammonium nitrate and sulfate) and elemental carbon (EC). Regarding metals, Ni and Cr were partitioned mainly in quasi-UFPs and could thus be of interest for epidemiological studies, given their high redox properties. Exposure of children to quasi-UFP mass and chemical species was assessed by comparing the concentrations measured at urban background and traffic areas schools. Finally, three main indoor sources across all size fractions were identified by assessing indoor / outdoor ratios (I / O) of PM species used as their tracers: human activity (organic material), cleaning products, paints and plastics (Cl− source), and a metallic mixed source (comprising combinations of Cu, Zn, Co, Cd, Pb, As, V and Cr). Our results support the need to enforce targeted legislation to determine a minimum "safe" distance between major roads and newly built schools to reduce exposure to traffic-derived metals in quasi-UFPs.
Highlights
Airborne ultrafine particles have been linked to adverse health effects, and more strongly than coarser particles because of the ability of the former to penetrate deeper into the respiratory tract and to translocate to other organs (Oberdorster, 2001; Kreyling et al, 2006; Paur et al, 2011; Strak et al, 2012; WHO, 2012, 2013)
Aerosol indoor / outdoor (I / O) relationships are impacted by particle size distributions, given that infiltration of outdoor particles into indoor air is most efficient for accumulation mode particles, while diffusion losses dominate for the lowest size ranges of ultrafine particles (< 100 nm) (Long et al, 2001)
For the experimental period (January to June 2012), mean quasi-UF mass concentrations were 25.6 μg m−3 outdoors (±10.7 μg m−3 standard deviation) and 23.4 ± 14.0 μg m−3 indoors, values which are significantly higher compared to those obtained in other regions of the world
Summary
Airborne ultrafine particles (defined as particles with aerodynamic diameters < 100–200 nm) have been linked to adverse health effects, and more strongly than coarser particles because of the ability of the former to penetrate deeper into the respiratory tract and to translocate to other organs (Oberdorster, 2001; Kreyling et al, 2006; Paur et al, 2011; Strak et al, 2012; WHO, 2012, 2013). Ultrafine particles may be either newly formed in the atmosphere through gas-to-particle conversion processes, or directly released by anthropogenic sources such as vehicular traffic (Sardar et al, 2005; Westerdahl et al, 2005). The ultrafine particle range is generally known to include the two lowest particle size modes, the nucleation and Aitken modes. The smallest particles are mostly formed from gas phase vapours via nucleation (nucleation mode, with aerodynamic diameter < 30 nm), a fraction of soot may be present in this particle size range. The Aitken mode particles are produced via growth from nucleation mode and/or emitted by a wide variety of anthropogenic sources (aerodynamic diameter between 30 nm and 100 nm (Hinds, 1999). Aerosol indoor / outdoor (I / O) relationships are impacted by particle size distributions, given that infiltration of outdoor particles into indoor air is most efficient for accumulation mode particles, while diffusion losses dominate for the lowest size ranges of ultrafine particles (< 100 nm) (Long et al, 2001)
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