Analysis of major and trace elements in ambient aerosols and their sources in European and Asian cities

Abstract

Atmospheric aerosols comprise a wide range of solid or liquid particles suspended in our atmosphere, contributing significantly to air pollution. Besides climate effects by scattering, absorption and modification of cloud properties, aerosols show negative acute and long-term health effects. Moreover, the negative impacts of aerosols on health are enhanced in heavily urbanized areas, especially in India and China, due to increased emissions from a wide array of sources and high population density. In order to develop effective mitigation strategies, the quantification and characterization of emission sources is an essential precondition. Aerosols are a complex mixture of thousands of individual compounds, among them elements or metals which have a high degree of source specificity and chemical stability, making them powerful chemical species for aerosol source apportionment (SA) studies. In this work, we exploited the use of a recently developed near real time ambient metals monitor (Xact, based on X-ray fluorescence spectrometry) across Europe (Härkingen, Switzerland, and Krakow, Poland) and Asia (Beijing, China, and Delhi, India) to measure highly time-resolved (30 min to 1 h) elemental data in different particulate matter size ranges (PM10 and PM2.5). In the first study, an advanced statistical SA technique was applied on the Härkingen dataset to explore the first use of an Xact for SA in Europe where the concentrations are considerably lower than in Asia. The SA results from this data revealed a strong influence from the secondary sulfate, followed by traffic emissions and dust-related (road and background) emissions, while lower contributions came from sea salt and industrial emissions. In addition to that, fireworks-related factors captured during the Swiss National Day celebration were also resolved. The comparison of elemental concentrations in European and Asian cities was the focus in the second study. Extremely high concentrations of elements were observed in Delhi as compared to Beijing and European cities. This study showed that the elements can be broadly classified into five groups on a global scale: dust-related (Si, Ca, Ti, Sr), traffic (Ba, Zr, Mn, Fe, Ni), solid fuel combustion (K), traffic/industrial (Cu), industrial/coal/waste burning emissions (Pb, Zn, S, Cl, Br). In addition to that, a strong enrichment of toxic elements was observed in these cities. In the third study, we developed a combined method to investigate sources and their potential source regions in the Delhi urban atmosphere. The SA analysis identified nine sources: S-rich, dust-related, brake wear, two for solid fuel combustion, and four for plume-like events. The analyses revealed strong source contribution enhancements during late night until early morning, consistent with enhanced emissions in stagnant ambient conditions. Furthermore, the dust-related and brake wear factors were strongly enriched in elemental PM10 while the remaining factors were mostly dominant in elemental PM2.5.