Abstract
Abstract. Ambient concentrations of trace elements with 2 h time resolution were measured in PM10–2.5, PM2.5–1.0 and PM1.0–0.3 size ranges at kerbside, urban background and rural sites in London during winter 2012. Samples were collected using rotating drum impactors (RDIs) and subsequently analysed with synchrotron radiation-induced X-ray fluorescence spectrometry (SR-XRF). Quantification of kerb and urban increments (defined as kerb-to-urban and urban-to-rural concentration ratios, respectively), and assessment of diurnal and weekly variability provided insight into sources governing urban air quality and the effects of urban micro-environments on human exposure. Traffic-related elements yielded the highest kerb increments, with values in the range of 10.4 to 16.6 for SW winds (3.3–6.9 for NE) observed for elements influenced by brake wear (e.g. Cu, Sb, Ba) and 5.7 to 8.2 for SW (2.6–3.0 for NE) for other traffic-related processes (e.g. Cr, Fe, Zn). Kerb increments for these elements were highest in the PM10–2.5 mass fraction, roughly twice that of the PM1.0–0.3 fraction. These elements also showed the highest urban increments (~ 3.0), although no difference was observed between brake wear and other traffic-related elements. All elements influenced by traffic exhibited higher concentrations during morning and evening rush hours, and on weekdays compared to weekends, with the strongest trends observed at the kerbside site, and additionally enhanced by winds coming directly from the road, consistent with street canyon effects. Elements related to mineral dust (e.g. Al, Si, Ca, Sr) showed significant influences from traffic-induced resuspension, as evidenced by moderate kerb (3.4–5.4 for SW, 1.7–2.3 for NE) and urban (~ 2) increments and increased concentrations during peak traffic flow. Elements related to regional transport showed no significant enhancement at kerb or urban sites, with the exception of PM10–2.5 sea salt (factor of up to 2), which may be influenced by traffic-induced resuspension of sea and/or road salt. Heavy-duty vehicles appeared to have a larger effect than passenger vehicles on the concentrations of all elements influenced by resuspension (including sea salt) and wearing processes. Trace element concentrations in London were influenced by both local and regional sources, with coarse and intermediate fractions dominated by traffic-induced resuspension and wearing processes and fine particles influenced by regional transport.
Highlights
Ambient particulate matter (PM) has long been recognized to have a detrimental effect on public health in urban areas (e.g. Dockery and Pope, 1994)
Total analysed mass measured by the rotating drum impactors (RDIs)-SR-XRF contributed on average 14 % to the total PM10 mass of 32 (5–74) μg m−3 at MR, 10 % to the mass of 23 (1.4–63) μg m−3 at NK and 7.4 % to the mass of 17 (0.5–58) μg m−3 at DE
Sampling with rotating drum impactors (RDIs) and subsequent measurements with synchrotron radiation-induced X-ray fluorescence spectrometry (SR-XRF) yielded trace element mass concentrations in PM10−2.5, PM2.5−1.0 and PM1.0−0.3 aerosol with a 2 h time resolution
Summary
Ambient particulate matter (PM) has long been recognized to have a detrimental effect on public health in urban areas (e.g. Dockery and Pope, 1994). Effective mitigation strategies require detailed, size-dependent characterization of particle composition and emission sources In addition to their direct effects on human health, metals and trace elements are of importance because their high source specificity and atmospheric stability make them effective tracers for source apportionment. Emissions from vehicle exhaust, industry and secondary aerosol are predominantly emitted and formed as PM1.0 or in PM2.5 (Bukowiecki et al, 2010; Harrison et al, 2011; Richard et al, 2011) Several of these sources have been directly linked to adverse health effects. The largest aerosol source of human toxicity in Barcelona was attributed to traffic activities (encompassing vehicle emissions, road dust and secondary nitrate), with fuel oil combustion and industrial emissions contributing to increased cancer risk (Reche et al, 2012). Turoczi et al (2012) observed higher toxicity from direct emissions (e.g. from traffic) than from photochemically processed aerosol
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