Molecular composition of biogenic secondary organic aerosols using ultrahigh resolution mass spectrometry: comparing laboratory and field studies

Numerous laboratory experiments have been performed in an attempt to mimic atmospheric secondary organic aerosol (SOA) formation. However, it is still unclear how close the aerosol particles generated in laboratory experiments resemble atmospheric SOA with respect to their detailed chemical composition. In this study, we generated SOA in a simulation chamber from the ozonolysis of α-pinene and a biogenic volatile organic compound (BVOC) mixture containing α- and β-pinene, Δ3-carene, and isoprene. The detailed molecular composition of laboratory-generated SOA was compared with that of background ambient aerosol collected at a boreal forest site (Hyytiälä, Finland) and an urban location (Cork, Ireland) using direct infusion nanoelectrospray ultrahigh resolution mass spectrometry. Kendrick Mass Defect and Van Krevelen approaches were used to identify and compare compound classes and distributions of the detected species. The laboratory-generated SOA contained a distinguishable group of dimers that was not observed in the ambient samples. The presence of dimers was found to be less pronounced in the SOA from the VOC mixtures when compared to the one component precursor system. The elemental composition of the compounds identified in the monomeric region from the ozonolysis of both α-pinene and VOC mixtures represented the ambient organic composition of particles collected at the boreal forest site reasonably well, with about 70% of common molecular formulae. In contrast, large differences were found between the laboratory-generated BVOC samples and the ambient urban sample. To our knowledge this is the first direct comparison of molecular composition of laboratory-generated SOA from BVOC mixtures and ambient samples.

Access to modified geiparvarins using Pd(0)-mediated C-C bond forming reactions

Geiparvarin is a natural product which contains both a 3(2H)-furanone and a coumarin moiety in its structure. The aim of this project was to investigate the use of Pd(0)-mediated C–C bondforming reactions to produce structurally modified geiparvarins. Chapter 1 consists of a review of the relevant literature, including that pertaining to the syntheses of selected naturally occurring 3(2H)-furanones. The known syntheses of geiparvarin and closely related analogues are examined, along with the documented biological activity of these compounds. The synthetic routes which allow access to 4-substituted-3(2H)-furanones are also described. Chapter 2 describes in detail the synthesis of a variety of novel structurally modified geiparvarins by two complementary routes, both approaches utilising Pd(0)-mediated crosscoupling reactions, and discusses the characterisation of these compounds. The preparation of 5-ethyl-3(2H)-furanones is described, as is their incorporation into geiparvarin and the corresponding 5″-alkylgeiparvarin analogues via formation and dehydration of intermediate alcohols. Halogenation of 5-ethyl-3(2H)-furanones and the corresponding geiparvarin derivatives is discussed, along with further reactions of the resulting halides. Preparation of 3″-arylgeiparvarins involving both Suzuki–Miyura and Stille reactions, using the appropriate intermediate iodides and bromides, is described. The application of Stille and Heck conditions to give 3″-ethenylgeiparvarin analogues and Sonogashira conditions to produce 3″-ethynylgeiparvarin analogues, using the relevant intermediate iodides, is also extensively outlined. Chapter 3 contains all of the experimental data and details of the synthetic methods employed for the compounds prepared during the course of this research. All novel compounds prepared were fully characterised using NMR spectroscopy, IR spectroscopy, mass spectrometry and elemental analysis; the details of which are included.

Real time analysis of atmospheric single particles in urban environments using aerosol time of flight mass spectrometry

In order to determine the size-resolved chemical composition of single particles in real-time an ATOFMS was deployed at urban background sites in Paris and Barcelona during the MEGAPOLI and SAPUSS monitoring campaigns respectively. The particle types detected during MEGAPOLI included several carbonaceous species, metal-containing types and sea-salt. Elemental carbon particle types were highly abundant, with 86% due to fossil fuel combustion and 14% attributed to biomass burning. Furthermore, 79% of the EC was apportioned to local emissions and 21% to continental transport. The carbonaceous particle types were compared with quantitative measurements from other instruments, and while direct correlations using particle counts were poor, scaling of the ATOFMS counts greatly improved the relationship. During SAPUSS carbonaceous species, sea-salt, dust, vegetative debris and various metal-containing particle types were identified. Throughout the campaign the site was influenced by air masses altering the composition of particles detected. During North African air masses the city was heavily influenced by Saharan dust. A regional stagnation was also observed leading to a large increase in carbonaceous particle counts. While the ATOFMS provides a list of particle types present during the measurement campaigns, the data presented is not directly quantitative. The quantitative response of the ATOFMS to metals was examined by comparing the ion signals within particle mass spectra and to hourly mass concentrations of; Na, K, Ca, Ti, V, Cr, Mn, Fe, Zn and Pb. The ATOFMS was found to have varying correlations with these metals depending on sampling issues such as matrix effects. The strongest correlations were observed for Al, Fe, Zn, Mn and Pb. Overall the results of this work highlight the excellent ability of the ATOFMS in providing composition and mixing state information on atmospheric particles at high time resolution. However they also show its limitations in delivering quantitative information directly.