Speeding up the Atmosphere: Experimental oxidation studies of ambient and laboratory aerosols using a flow reactor

Research output: ThesisDoctoral Thesis (compilation)

Abstract

Apart from gases, the air we breath consist of tiny, so called, aerosol particles. A cubic metre of air in a relatively clean environment can consist of several billion aerosol particles. The impact of these particles on human health and on climate is significant. According to WHO, particles affect more humans than any other pollutant, and is closely related to mortality and morbidity. Further, it has been estimated that anthropogenic particles have cooled the climate, masking up to 50% of the warming caused by greenhouse gases. A large portion of the smallest particles consists of organic compounds, much of which is formed by atmospheric oxidation reactions. This material is called secondary organic aerosol (SOA). In this thesis, submicron secondary aerosol particles have been investigated using an oxidation flow reactor (OFR). Inside the reactor, large concentrations of oxidants produce secondary particulate material in a matter of minutes, thereby speeding up the naturally occuring atmospheric processes.

In two laboratory studies, we have investigated the effect of mixing anthropogenic primary and secondary particles with biogenic SOA. In line with expectations, the anthropogenic and biogenic organic precursors mixed, and, in a non-linear way, formed more particulate mass than would otherwise be the case. Further, the effect of wet anthropogenic salt particles on SOA formation was investigated. The produced SOA mass in the presence of wet particles was significantly higher than if the particles were dry. This effect is believed to be very important in the atmosphere since water is always present. In both these studies it was shown that the SOA mass formed in OFRs at low particle mass concentrations, is underestimated due to the limited time for condensation of vapours in the reactor.

In a separate study, the SOA formation from biomass burning was investigated. Biogenic SOA dominates on a global scale, but very high concentrations are only formed in the proximity of anthropogenic sources. It was shown that SOA formation from the emissions of a modern wood stove can be large enough to dominate over the primary particle emissions. To estimate the secondary particle formation potential of ambient air, two field studies were performed. In both studies, the simulated atmospheric processing of the background air did not produce much secondary particle mass. From this, it can be concluded that the chosen measurement sites were relatively clean, but the results also point to the efficiency of atmospheric processing. However, in one of the studies, targeting ship emissions at a coastal site, plumes of secondary material, of the same magnitude as the background aerosol particle concentration, was formed. This demonstrates the importance of considering atmospheric processing and the advantage of using OFRs in field studies.

The relative importance of SOA in the atmospheric aerosol is believed to increase in the future. Due to complex feedbacks and the many variables affecting SOA formation, it is difficult to parameterize in a simple enough manner fit for global models. Both detailed and large-scale processes needs further investigation to improve estimations of SOA radiative forcing and the anthropogenic effect on biogenic SOA. The popularity of oxidation flow reactors in SOA research is likely to increase. The five original research manuscripts included in this thesis contributes specifically to the OFR research community, but also to improved understanding of SOA formation in the the anthropocene in general.

Details

Authors
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Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Environmental Sciences
  • Meteorology and Atmospheric Sciences

Keywords

  • Secondary organic aerosols, oxidation flow reactor, volatile organic compounds, climate
Original languageEnglish
QualificationDoctor
Awarding Institution
Supervisors/Assistant supervisor
Award date2017 Dec 15
Place of PublicationLund
Publisher
  • Lund University, Faculty of Science, Centre for Environmental and Climate research (CEC) & Department of Physics, Division of Nuclear Physics
Print ISBNs978-91-7753-495-2
Electronic ISBNs978-91-7753-496-9
Publication statusPublished - 2017 Nov
Publication categoryResearch

Bibliographic note

Defence details Date: 2017-12-15 Time: 09:15 Place: Lecture hall “Blå hallen”, Ecology building, Sölvegatan 37, Lund External reviewer(s) Name: Hoyle, Christopher Title: Dr. Affiliation: WSL Institute for Snow and Avalanche Research SLF, Switzerland ---

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