Field and laboratory studies of aerosol formation from halogenated precursor gases
Final Report Abstract
This project was part of the HaloProc research unit on natural halogenation processes, and explored the impact of reactive halogen species on aerosol formation in field and laboratory experiments. Field studies were focused on the Lake King salt lake area in Western Australia. New particle formation events were frequently observed and characterized by measuring the temporal evolution of the submicron aerosol size distributions, and collecting aerosol samples for subsequent chemical analysis. 9 out of 11 measurement days in 2013 showed secondary aerosol formation with particle growth rates from 2.9 to 25.4 nm h^-1. Raman spectroscopy and ultrahigh resolution mass spectrometry revealed a contribution of organohalogen compounds (mostly organochlorine) to the secondary organic aerosol, however, organosulfate and organonitrate formation seemed to play a larger role in the studied environment. Nevertheless, a new experimental approach that made use of a mobile Teflon chamber set up above the salt crust and the organic-rich mud layer of various salt lakes directly linked new particle formation to the hypersaline environment of Western Australia. For more detailed process studies, these field results provided realistic scenarios and constraints for simulation experiments in the laboratory. Salt lake conditions were successfully simulated in aerosol chamber experiments and showed secondary aerosol formation in the presence of light and organic precursor compounds. The particle formation dynamics and the chemical speciation of aerosol samples, which were collected from the chamber experiments and analyzed by Raman spectroscopy and mass spectrometry, indicated a coupling of aqueous phase chemistry and secondary aerosol formation. In particular, the Fe(II) concentrations of the simulated salt lakes were a key control for the intensity of new particle formation. In saline environments with low pH values and high solar radiation, Fe(II) might be converted to Fe(III) in the presence of organic matter in a Fenton-like reaction, which can act as a major source for highly reactive OH radicals in the aqueous phase. On the one hand, this expands the potential oxidation pathways for organic compounds, which led to a larger chemical diversity. On the other hand, Fe(II)-controlled aqueous phase chemistry competes with secondary aerosol formation in the gas phase, which led to reduced particle formation in our experiments. While it is premature to fully incorporate these findings in chemistry box models, additional laboratory studies provided experimental data that will guide the development of model parameterizations, e.g., for the organic aerosol yield from the oxidation of organic compounds by chlorine and bromine, or for reactive bromine loss due to uptake in secondary organic aerosol. In conclusion, this project bridged gaps between field studies of halogen-influenced new particle formation in the real world and laboratory experiments within the HaloProc research unit. The project results contribute to a better understanding of new particle formation in salt lake environments, which may lead to enhanced numbers of cloud condensation nuclei. However, the unexpectedly strong interaction of aqueous phase chemistry and new particle formation raises new questions about secondary aerosol formation in hypersaline environments and its atmospheric and environmental implications. Thus, the field and laboratory experiments performed in this project considerably expanded the perspective on the role of reactive halogen species in atmospheric secondary aerosol formation.
Publications
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(2013) Halogen-induced organic aerosol (XOA): A study on ultra-fine particle formation and time-resolved chemical characterization. Faraday Discussions 165, 135-149
Ofner, J., Kamilli, K.A., Held, A., Lendl, B., Zetzsch, C.
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(2015) Chemometric analysis of multisensor hyperspectral images of precipitated atmospheric particulate matter. Analytical Chemistry, 87, 9413-9420
Ofner, J., Kamilli, K.A., Eitenberger, E., Friedbacher, G., Lendl, B., Held, A., Lohninger, H.
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(2015) New particle formation above a simulated salt lake in aerosol chamber experiments. Environmental Chemistry, 12, 489-503
Kamilli, K.A., Ofner, J., Lendl, B., Schmitt-Kopplin, P., Held, A.
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(2015) Organic particle formation in halogen-influenced environments. PhD thesis, Universität Bayreuth, Bayreuth, Germany, 93 pp.
Kamilli, K.A.
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(2016) How salt lakes affect atmospheric new particle formation: A case study in Western Australia. Sci. Total Environment, 573, 985-995
Kamilli, K.A., Ofner, J., Krause, T., Sattler, T., Schmitt-Kopplin, P., Eitenberger, E., Friedbacher, G., Lendl, B., Lohninger, H., Schöler, H., Held, A.
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(2016) Tip-Enhanced Raman Spectroscopy of atmospherically relevant aerosol nanoparticles. Analytical Chemistry
Ofner, J., Deckert-Gaudig, T., Kamilli, K.A., Held, A., Lohninger, H., Deckert, V., Lendl, B.
