An investigation of the secondary organic aerosol formation and volatility in mixtures of anthropogenic and biogenic precursors using smog chamber experiments

  • Aristeidis Voliotis

Student thesis: Phd

Abstract

Aerosol particles originate from both primary and secondary sources with implications on climate, air quality and human health. Secondary organic aerosols (SOA) comprise a large fraction of the total aerosol mass and are formed from the oxidation of anthropogenic and biogenic volatile organic compounds (AVOC and BVOC, respectively). The VOC emission rates and sources are diverse, leading to a highly complex SOA composition that can substantially vary temporarily and spatially. Until recently, the SOA mass was thought to be independently formed from the oxidation of each VOC precursor, however recent evidence demonstrated that the molecular interactions of the oxidised products may alter the SOA formation potential. This could partly explain our inability to predict the SOA loadings and impacts that are still highly uncertain. This thesis explores the photochemical SOA formation, composition and volatility derived from the mixing of various key AVOC (o-cresol) and BVOC (a-pinene and isoprene) by conducting experiments in an atmospheric simulation chamber. In order to assess the capabilities and limitation of the facilities used in this thesis, a detailed characterisation of the Manchester Aerosol Chamber (MAC) was conducted. This revealed the importance of regularly characterising such facilities for losses of particles and gases and highlighted the need for the development of a unified framework to characterise the atmospheric simulation chamber facilities. The concept of initial iso-reactivity was conceived that enabled the preparation of VOC mixtures that had comparable reactivity towards the assumed dominat oxidant (OH) in all the systems examined. The SOA formation potential was found to be enhanced, supressed or unaffected by the mixing of the precursors, suggesting that the effect of mixing is system-dependent and not straightforward. Similarly, certain mixed systems showed to have higher SOA particle volatility than that observed in single precursor experiments (e.g., o-cresol/isoprene), others showed lower (e.g., a-pinene/o-cresol and a-pinene/o-cresol/isoprene), while others appeared to be unaffected (e.g., a-pinene/isoprene). All the mixed systems however showed clear differences in the SOA chemical composition. Two main processes were observed in all the mixed VOC systems; the suppression in the formation of products that formed in single precursor systems and the formation of unique products in each mixture. The trade-off between these two processes are likely, at least partly, defining the SOA composition in mixed VOC systems that in turn may affect the SOA formation and volatility.
Date of Award31 Dec 2021
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRami Alfarra (Supervisor) & Gordon Mcfiggans (Supervisor)

Keywords

  • Secondary organic aerosols
  • Volatility
  • Chamber

Cite this

'