Organic particle formation in halogen-influenced environments

Atmospheric aerosols are an important topic in atmospheric research, motivated by their impact on climate, human health and heterogeneous chemistry. Secondary aerosol formation from the reaction of organic trace gases and reactive halogen species can act as an important natural source of organic aerosol. In order to better understand these reactions, aerosol formation from the reaction of α-pinene with chlorine and bromine was studied in laboratory experiments. New particle formation was initiated about five times faster by chlorine than by bromine. While new particle formation was observed at mixing ratios of 2.5 ppb Cl2 and 10 ppb α-pinene, new particle formation with bromine was not observed below 10 ppb Br2 and 10 ppb α-pinene. The formation of halogenated organic aerosol was confirmed by infrared spectroscopy (FTIR). To investigate the role of halogens in natural organic aerosol formation, a salt lake region in Western Australia, which is rich in reactive halogen species and organic compounds, was chosen as measurement site. On nine out of eleven measurement days and at five lakes, new particle formation was identified by measuring particle size distributions with a custom-built mobility analyzer (DMPS). With a mobile Teflon chamber set up at the lakeshore, particle formation was directly related to salt lake emissions. Due to enrichment of organic precursors inside of the chamber, particle formation started earlier and particle growth was faster than in the ambient air. Based on these field measurements, a salt lake environment was simulated in the laboratory. By systematic variation of the experimental conditions, the presence of light and organic precursor gases were identified as essential for new particle formation. Iron salt concentrations in the lake mixture controlled the intensity and the growth rates during new particle formation. Iron salts may catalyze additional oxidation reactions of organic compounds in the aqueous phase by a Fenton-like reaction mechanism. In this work, high FeII concentrations led to less new particle formation, which indicates a competition of oxidation of organic compounds in the aqueous phase and the gas phase. Organic aerosol samples from the field and from the laboratory were analyzed by ultrahigh resolution mass spectrometry, Raman spectroscopy, and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. Halogenated organic compounds were unequivocally identified, however, their contribution to new particle formation seems to be minor. The results show a large contribution of oxidized organic compounds as well as nitrogen- and sulfur-containing organic compounds to the formed aerosol mass.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2015

Author dc:creator

• Kamilli, Katharina A.

Contributors dc:contributor

• Held, Andreas

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/2727/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:2727