The contribution of non-exhaust, mineral and marine sources of particulate matter (PM) can be quantified by measuring elements that are characteristic of these sources. For example, barium is accepted as a good tracer for brake wear, while silicon is major component of many minerals and we all know that sodium and chloride make sea salt. However, measuring the concentration of some of these trace elements in ambient air at the highly time resolved resolution which allows them to be linked to activity and meteorological data is one of the most challenging areas in modern aerosol measurement.

During the NERC ClearfLo study, this was undertaken at three sites and in three PM size fractions in and around London. The exercise was undertaken during 2012 summer and winter field campaigns by researchers from the Paul Scherrer Institute (Switzerland) in association with other ClearfLo research groups including King’s College London. By measuring the concentrations simultaneously at rural, urban background and kerbside locations, the researchers were able to identify which elements were elevated due to urban and traffic sources. Kerbside increments were assigned to brake wear elements (Cu, Zr, Mo, Sn, Sb, Ba) and non brake wear traffic emissions (Cr, Mn, Fe, Zn, Pb).

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. Furthermore, a uniform effect of long range transport processes was demonstrated at all sites using tracers such as P, S, K, Zn, Br, Pb in the fine PM fraction.

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Item date 17/06/2015