Mass spectrometric analysis of particulate matter in remote regions and highly polluted Chinese and Iranian megacities

Abstract

The investigations in the present work are intended to contribute to the understanding of the health and environmental impacts of aerosol pollution, both in remote regions and in strongly polluted megacities. This was achieved by a combination of different instrumental and methodological approaches. First, in-situ single-particle analysis and its evaluation, based on multivariate statistical methods, was methodologically advanced using the example of a comparative measurement of standard samples in the laboratory and of online measurements on the Jungfraujoch high altitude research station at 3580 m asl in the Swiss Alps. In order to rationalize single-particle data, weather conditions, wind speed and wind direction as well as the geographical position during the measurement were taken into account. It was found that during the field measurements at the Jungfraujoch site, Sahara desert storm events were a major source for less aged iron- and silicon-rich mineral particles. Between those events the particle population was dominated by inorganic carbonaceous compounds. Both types of particles increase the local temperature and accelerate snowmelt, either by reducing snow albedo or by absorbing light over a broad spectral range. Secondly, in order to be able to address the environmental and health related factors in greater detail, particles from two heavily polluted megacities in Hangzhou, China and Tehran, Iran were extensively characterized. Filter samples were collected and measured by high-resolution mass spectrometry imaging to assign organic hydrocarbons and more complex inorganic compounds. This enabled analysis of intact organic molecules with high mass resolution and high mass accuracy. The novel methodological approach, in which the surface of particle quartz filter samples was scanned under atmospheric pressure using a 343 nm (Yb:YAG) laser (lateral resolution about 50 µm), enabled spatially resolved determination of the molecular particle composition. More than 3200 inorganic and organic compounds were specifically assigned to individual particles based on their exact mass and location on the filter surface. Particle sources could be easily distinguished from each other by means of characteristic mass spectrometric patterns using statistical clustering methods. Standard addition methods were also used to quantify polyaromatic hydrocarbons (PAHs) on the surface of the filters. By correlating the quantitative data with the spatially resolved particle measurements, it was possible to make well-founded statements about the respective particle pollution and its causes on site. Levels of heavy metals and harmful organic compounds, primarily from anthropogenic sources, were significant in both cities. However, higher concentrations of PAHs and a greater number of heavy metal compounds were found in the samples from Tehran. Since total particle pollution in Tehran during sampling was lower than in Hangzhou, these values are extremely alarming and demonstrate the non-compliance with and the lack of air pollution control strategies in the eastern Mediterranean region. Finally, it was shown that both methods require little or no sample preparation and provide excellent results in terms of speed, accuracy and selectivity.