Polluting Particles: Direct Analysis of Organic Aerosol via PTR-TOFMS

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Ship diesel emissions

Several coastal metropolitan areas suffer from bad air quality that is partly affected by the emissions from large cargo ships, cruise liners and harbor activities. To improve air quality, sulfur emission control areas were recently established that enforce a transition from residual heavy fuel oil (HFO) towards low-sulfur distillate marine gas oil (MGO) in declared coastal areas. Inorganic particulate matter (e.g. sulfate particles) can be reduced efficiently, but little is known about the particulate organic fraction in ship exhaust that accounts for ~15 to 80% of the total particulate emissions for HFO and MGO respectively. To study the chemical composition in unprecedented detail, Charon PTR-TOFMS was installed to identify and quantify the total emission of organic aerosol from a marine test bench engine that was operated on HFO and MGO [8]. In both fuel operation modes a series of aliphatic hydrocarbons in the C20-to-C39 range was identified, which are typical main constituents of lubricating oils.

Figure 2 displays Charon PTR-TOFMS mass spectra of measured marine engine exhaust operated on HFO and aerosolized unburned lubricant oil. Only little difference between both mass spectra is visible. Total emissions of lubricating oil up to 183 mg kW^-1 h^-1 were detected. This value resembles typical oil loss rates of marine four-stroke trunk piston engines. Potential biological effects of lubricating oil components should be investigated in more detail.

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Ambient air study

A morning rush-hour urban air-pollution event was measured in April 2017 in Innsbruck, Austria, and serves as an excellent example for the unique analytical performance of Charon PTR-TOFMS (figure 3). Cold temperatures and a strong inversion led to a quick accumulation of primary particulate matter emitted from traffic and domestic heating. Total organic aerosol concentrations quickly increase from around 1 µg/m³ to nearly 20 µg/m³. Good temporal agreements with in parallel Scanning Mobility Particle Sizer (SMPS) measurements are achieved. The chemical finger-print includes the dominant biomass burning tracer levoglucosan, traffic markers including condensed polycyclic aromatic hydrocarbons (PAHs) and series of potential aliphatic hydrocarbons, the main constituents of lubricant oils.

Such multitudes of highly time-resolved chemical signals are perfect inputs for an apportionment of emissions to specific sources. In urban environments such sources include direct emissions from traffic, domestic heating, and cooking or secondary sources from e.g. biogenic emissions or solvents. With an example of Innsbruck in October 2015 (see figure 4, online), the biggest source for particulate organic matter clearly is biomass burning. Biomass burring organic aerosol (BBOA) tracers are clearly dominated by the anhydrosugar levoglucosan (C₆H₁₁O₅⁺) [4]. This does not come as a surprise, as wood is commonly used for domestic heating in this area. Another urban emission source comes from traffic (traffic POA). One well known group of compounds primarily emitted from traffic are condensed PAHs. Nevertheless, source apportionment shows us that biomass-burning accounts to 74% of the total daily emission and is therefore the biggest source for toxic PAHs. A reduction of wood burning for domestic heating would clearly improve air quality in winter-time, especially in alpine valleys with limited air exchange.

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Outlook: Charon Goes Airborne

Recently, Charon was invited to go airborne and participate in NASA’s Student Airborne Research Project (SARP) to study the air quality in the proximity of Los Angeles (USA) onboard of NASA’s DC-8 Airborne Science Laboratory. During this campaign that will take place in July 2018, Charon will analyze particulate organic aerosol with a special focus on potential wild-fire emissions, traffic and transportation emissions in the proximities of the LAX airport and the Los Angeles Harbor as well as secondary biogenic emissions in California’s Central Valley, one of the most productive agricultural areas in the world.

Charon Goes Airborne

During all these studies, Charon PTR-TOFMS has proven to be a versatile and robust analytical instrument and therefore we now start to explore the use of Charon on mobile PTR-TOFMS platforms based on
ioniTOF mass spectrometers which are compact and modular time-of-flight systems for research & OEM, developed and manufactured by Ionicon (s. LAB Info box).

References

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[6] G. I. Gkatzelis, R. Tillmann, T. Hohaus, M. Müller, P. Eichler, K.-M. Xu, P. Schlag, S. H. Schmitt, R. Wegener, M. Kaminski, et al., Atmos. Meas. Tech. 2018, 11, 1481–1500.

[7] W. Tan, L. Zhu, T. Mikoviny, C. J. Nielsen, A. Wisthaler, P. Eichler, M. Müller, B. D’Anna, N. J. Farren, J. F. Hamilton, et al., J. Phys. Chem. A 2018, DOI 10.1021/acs.jpca.8b01862.

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* M. Müller, P. Sulzer, J. Herbig, L. Märk: Ionicon Analytik GmbH, Innsbruck/ Austria

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