Speaker
Ms
Suzanne Visser
(MSc)
Description
The identification and quantification of particle sources has long proven challenging due to the complex composition of ambient aerosol. Measurements of trace elements provide uniquely source-specific information; e.g. barium and copper are emitted by traffic sources, while vanadium and nickel are linked to heavy oil combustion. The power of source apportionment by trace elemental analysis is greatly enhanced by simultaneous measurements of complementary aerosol species. Optimization of trace elemental data requires measurements with sufficient temporal resolution to distinguish sources with different characteristic diurnal patterns such as traffic and sea salt, while size-resolved measurements can help resolve different source classes with similar composition, e.g. iron from resuspension appears in PM10-2.5 while brake wear processes appear in PM1. Here we present highly time- and size-resolved measurements of trace elements as part of the ClearfLo (Clean Air for London) 2012 field campaign, a multinational collaborative effort to investigate boundary layer pollution in and around London, UK.
Sampling was performed at several sites in and around London during two Intensive Observation Periods (IOPs) in 2012. During the winter IOP (11 Jan. to 8 Feb.) particulate matter was sampled at a site with heavy traffic (Marylebone Road, MR) and an urban background site (North Kensington, NK) in London, and at a rural site in Detling, southeast of London. Summer sampling took place at the two London sites from 18 July till 22 August, a period which included the Olympic Games. Rotating drum impactors (RDIs) collected particles in three size bins (PM10-2.5, PM2.5-1.0 and PM1.0-0.1) with a high time resolution of 2 h, instead of more common 24 h sampling times. The elemental composition of the samples was analysed by synchrotron radiation induced X-ray fluorescence spectrometry (SR-XRF) at the Swiss Light Source (SLS, Paul Scherrer Institute, CH) and at HASYLAB (Deutsches Elektronen-Synchrotron, DE). The RDI SR-XRF setup provides quantification of elements with atomic number 11 (sodium) to 82 (lead) with a detection limit on the order of a few pg.
We will show median diurnal variations of selected elements in PM10-2.5 during the winter IOP. The rush hour peaks for iron and barium commonly observed in a street canyon with stop-and-go traffic. Ba is typically related to brake wear and elevated concentrations are thus likely at such a site. Elevated concentrations during daytime for mineral dust elements like aluminium and calcium occur from continuous resuspension at MR. NK shows lower levels due to dilution of air during transport from the traffic to the urban background site. Rather constant values were observed for e.g. sodium (Na) and magnesium (Mg). These sea salt elements are likely advected throughout the day, but the elevated values at MR indicate local emissions as well. Correlations with e.g. black carbon, nitrogen oxides and meteorological conditions will enhance the source separation of the trace elements.
This work was funded by the ClearfLo project (NERC grant NE/H00324X/1), the SNF (grant 200021_132467 /1) and the European Community’s Seventh Framework Programme (FP7/2007-2013, grant n°312284).
Primary author
Ms
Suzanne Visser
(MSc)
Co-authors
Dr
Markus Furger
(Paul Scherrer Institute)
Prof.
Urs Baltensperger
(Paul Scherrer Institute)
Mr
Uwe Flechsig
(Paul Scherrer Institut)
