New particle formation above a simulated salt lake in aerosol chamber experiments

Abstract

Environmental context Deforestation in Western Australia beginning in the mid-19th century led to a considerable change of the land surface, and Western Australia is now suffering more often from droughts. Particle formation induced by salt lakes has been identified as a potential control factor for changed precipitation patterns. This study aims to determine key factors involved in the particle formation process by simulating a simplified salt lake in an aerosol chamber in the laboratory. Abstract In recent field experiments, particle formation has been observed above salt lakes in Western Australia and related to changes in regional precipitation patterns. This work investigates the particle formation potential above a simulated salt lake in aerosol chamber experiments under various conditions. The salt lake mixture comprised fixed concentrations of NaBr, NaCl and Na2SO4, and varying concentrations of FeSO4 and FeCl3. Further, an organic mixture of 1,8-cineol and limonene was added under dark and light conditions. Both the presence of organic compounds and of light were found to be essential for new particle formation in our experiments. There were clear indications for conversion of FeII to FeIII, which suggests a Fenton-like reaction mechanism in the system. Contrary to the idea that a Fenton-like reaction mechanism might intensify the oxidation of organic matter, thus facilitating secondary organic aerosol formation, the observed particle formation started later and with lower intensity under elevated FeII concentrations. The highest particle number concentrations were observed when excluding FeII from the experiments. Chemical analysis of the formed aerosol confirmed the important role of the Fenton-like reaction for particle formation in this study. Ultrahigh-resolution mass spectrometry and Raman spectroscopy provide analytical proof for the formation of organosulfates and halogenated organic compounds in the experiments presented. Even though halogens and organic precursors are abundant in these experimental simulations, halogen-induced organic aerosol formation exists but seems to play a minor overall role in particle formation.