New analytical techniques for time-resolved chemical analysis of organic matter in atmospheric aerosol particles

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Aerosol particles in the atmosphere have impact on global climate, ecosystems, and human health (World Health Organization 2016, Shiraiwa et al. 2017, Andreae and Crutzen 1997). Besides the subdivision into different particle sizes particulate matter (PM) can also be characterized by its different chemical composition. Most commonly is PM sampled with offline sampling, where PM is sucked through a filter with a well-defined air flow for multiple hours up to days. In a second step, the analysis is carried out in the laboratory using an analytical measurement technique often with a mass spectrometry (MS) coupling. A detailed characterization of the chemical composition is possible, but only limited information on the short-term temporal variations of the respective substance concentrations are accessible. A broadly applied alternative to the classic offline approach is online MS, where the aerosol is directly sampled and analysed with high time resolution. The most common are aerosol mass spectrometer (AMS), where molecules are fragmented during ionization, which only allows a chemical description in rough groups of substances. Especially is the chemical composition of organic aerosol particles highly variable over time and is only incompletely represented by current sampling and measurement methods. Therefore, this project focusses on gaining new insights into sources, sinks, and transformations of such particles by applying two new and complementary approaches for a time-resolved chemical characterization: i. an automated offline filter-plate based particle sampler for hourly sampling intervals. ii. an extractive electrospray ionization (EESI) Orbitrap-MS for highly time-resolved online analysis. Complementary information from both approaches is intended to improve understanding in formation processes, potential reactions, sinks, and emission sources of organic aerosol particles. In order to achieve this, both devices must first be extensively tested and characterized. The first test phase is to take place at the aerosol chamber of TROPOS, which is well-suited for such characterization due to its controllable environmental conditions. For further device evaluation, this phase is followed by first ambient applications of the new instruments in short field campaigns at TROPOS in Leipzig, Germany. These first chamber and ambient applications are intended to optimize the instruments and overcome potential initial challenges in their operation. Finally, several measurement campaigns at the rural TROPOS research station Melpitz, Germany, are foreseen. In this phase, the main aims are i) to measure time-resolved concentration profiles of several organic markers to identify sources and formation processes from ambient data, and ii) to explore potential synergetic insights that can be obtained from applying both the offline and the online approach in parallel.