Stable metal isotopes as discriminators of combustion and non-combustion sources in atmospheric particulates: A proof of concept study using two megacities in China

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Combatting air pollution is one of the great challenges urban environments of the future face. Of great concern, in particular, is the increase in particulate matter emissions and the associated high concentration of toxic metals. Identifying the sources of the toxic metals remains one of the great challenges because the methods developed so far (based on statistical methods) are often inconclusive and expensive (computational and analytically). To this end, the application of isotope ratios is of great interest because with this technique we can specifically target elements of interest. The development of a new generation of plasma source mass spectrometers has enabled to apply isotopes systematics for source tracing of metals and recent work pioneered by a group of researchers at Imperial College London suggests that these new isotope systems enable to identify sources of Cu and Zn in urban particles. Work in major urban cities around the world showed significant isotopic variations and there is strong evidence that isotopically very heavy and light isotope signatures point to sources from industrial combustion while the range in-between points to sources derived from vehicular emissions, i.e. tires and brakes. If this can be confirmed, then a major new tool in identifying sources of these toxic metal will enable urban planners to address and combat air pollution in their city. To test this hypothesis, I – as part of a team at Imperial College London – propose to analyze the isotopic composition of aerosols in two megacities with distinct different emission scenarios. Hong Kong is dominated by particulate matter emissions derived from traffic and Beijing is dominated by coal emissions during winter and traffic in the summer. We aim to analyze the isotopic compositions of these aerosols over the span of one whole year and, additionally, the key sources (tires and brakes from cars, coal seams from China, emissions from smelters and other combustion emissions). To support the source identification, we will carry out mineralogical and geochemical analyses of the particulate aerosols. Finally, we will critically compare calculated source apportionment using isotopic and non-isotopic techniques and evaluate the potential of this new tracer.