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

治理空气污染是未来城市环境面临的巨大挑战之一。尤其令人极为关切的是微粒物质排放的增加以及与之相关的有毒金属的高浓度。确定有毒金属的来源仍然是一个巨大的挑战，因为迄今为止开发的方法（基于统计方法）往往是不确定的和昂贵的（计算和分析）。为此，同位素比率的应用是非常有趣的，因为有了这种技术，我们可以专门针对感兴趣的元素。新一代等离子体源质谱仪的发展使同位素系统学能够应用于金属的来源追踪，最近由伦敦帝国理工学院的一组研究人员率先开展的工作表明，这些新的同位素系统能够识别城市颗粒中Cu和Zn的来源。在世界各地主要城市开展的工作显示出显著的同位素变化，有强有力的证据表明，同位素非常重和很轻的特征指向来自工业燃烧的来源，而介于两者之间的范围指向来自车辆排放的来源，即轮胎和刹车。如果这一点能够得到证实，那么确定这些有毒金属来源的主要新工具将使城市规划者能够处理和对抗城市中的空气污染。为了验证这一假设，我——作为伦敦帝国理工学院团队的一员——提议分析两个有着截然不同排放情景的大城市中气溶胶的同位素组成。香港主要是交通产生的颗粒物排放，北京主要是冬季和夏季交通产生的煤炭排放。我们的目标是在一整年的时间里分析这些气溶胶的同位素组成，此外，还分析了主要来源（汽车的轮胎和刹车、中国的煤层、冶炼厂的排放和其他燃烧排放）。为支持来源鉴定，我们将对颗粒气溶胶进行矿物学和地球化学分析。最后，我们将严格比较使用同位素和非同位素技术计算的源分配，并评估这种新示踪剂的潜力。

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.