Kerb and urban increment of highly time-resolved trace elements in PM10, PM2.5 and PM1.0 winter aerosol in London during ClearfLo 2012

摘要

Ambient concentrations of trace elements with 2 h time resolution weremeasured in PM, PM and PM size rangesat kerbside, urban background and rural sites in London during winter 2012.Samples were collected using rotating drum impactors (RDIs) and subsequentlyanalysed with synchrotron radiation-induced X-ray fluorescence spectrometry (SR-XRF).Quantification of kerb and urban increments (defined askerb-to-urban and urban-to-rural concentration ratios, respectively), andassessment of diurnal and weekly variability provided insight into sourcesgoverning urban air quality and the effects of urban micro-environments onhuman exposure. Traffic-related elements yielded the highest kerbincrements, with values in the range of 10.4 to 16.6 for SW winds (3.3–6.9for NE) observed for elements influenced by brake wear (e.g. Cu, Sb, Ba) and5.7 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 thePM mass fraction, roughly twice that of the PM fraction. These elements also showed the highest urban increments(~ 3.0), although no difference was observed between brakewear and other traffic-related elements. All elements influenced by trafficexhibited higher concentrations during morning and evening rush hours, and onweekdays compared to weekends, with the strongest trends observed at thekerbside site, and additionally enhanced by winds coming directly from theroad, consistent with street canyon effects. Elements related to mineraldust (e.g. Al, Si, Ca, Sr) showed significant influences fromtraffic-induced resuspension, as evidenced by moderate kerb (3.4–5.4 for SW,1.7–2.3 for NE) and urban (~ 2) increments and increasedconcentrations during peak traffic flow. Elements related to regionaltransport showed no significant enhancement at kerb or urban sites, with theexception of PM sea salt (factor of up to 2), which may beinfluenced by traffic-induced resuspension of sea and/or road salt. Heavy-duty vehicles appeared to have a larger effect than passenger vehicles onthe concentrations of all elements influenced by resuspension (including seasalt) and wearing processes. Trace element concentrations in London wereinfluenced by both local and regional sources, with coarse and intermediatefractions dominated by traffic-induced resuspension and wearing processesand fine particles influenced by regional transport.