Biogenic secondary organic aerosol (SOA) particles, produced by forest ecosystems across the globe, are principal, yet poorly understood constituents in the climate system. These atmospheric particles form when biogenic volatile organic compounds (BVOCs) react with atmospheric oxidants, leading to increasingly lower volatility oxidation products that partition into the condensed phase through various gas-to-particle conversion pathways. Biogenic SOA particles impact Earth’s radiative budget by scattering and absorbing solar radiation as well as serving as seed nuclei that promote cloud formation. However, uncertainties with regard to the climate impacts of biogenic SOA particles remain difficult to constrain due to their inherently diverse sources, formation mechanisms, molecular constituents, properties, and tropospheric lifetimes. Given that heterogeneous phenomena are intrinsically involved SOA processes and interactions and the gas/particle interface is the first point-of-contact for surrounding species, this work focuses on the chemistry occurring at atmospheric surfaces and interfaces. In this thesis, we investigate the structure, properties, orientation, and reactivity of molecular constituents that partition to atmospherically relevant surfaces with the central goal of gaining molecular-level insights into the surface chemistry of biogenic SOA particles. To do so, we integrate organic synthesis, aerosol generation and collection, and surface science, with an emphasis placed on the utility of nonlinear vibrational spectroscopy and dynamic surface tension measurements. We present syntheses and surface-specific analyses of oxidation products derived from α-pinene and β-caryophyllene, the most atmospherically abundant monoterpene and sesquiterpene, respectively. To explore the influence of various oxidation products on SOA-mediated cloud activation, we describe measurements of the surface tension depression of aqueous droplets containing a suite of synthesized monomeric α-pinene and β-caryophyllene ozonolysis products. Using vibrational sum frequency generation (SFG) spectroscopy, we report spectroscopic benchmarking experiments aimed at qualitatively investigating the surface spectra of aerosol material generated from the ozonolysis of β-caryophyllene. We also discuss SFG measurements of the β-caryophyllene-derived oxidation products at air/aqueous interfaces in order to further understand their structural organization in conditions applicable to cloud droplet formation scenarios. Expanding beyond the synthesis and analysis of this suite of molecular constituents, we summarize a variety of studies that have laid the groundwork for three main future research avenues towards studying increasingly complex systems relevant to SOA surface science. Specifically, we detail (1) collaborative work utilizing the monomeric oxidation products, (2) efforts to probe atmospheric surfaces under simulated environmental conditions, (3) spectroscopic experiments on field-collected samples, and (4) studies towards the synthesis and analysis of dimeric SOA constituents. The discussed findings overall emphasize the fundamental importance of exploring the molecular surface chemistry of biogenic SOA particles in the atmosphere.

Creator

• Be, Ariana Gray

DOI

• https://doi.org/10.21985/n2-jmq1-yg35

Subject

• Organic chemistry
• Physical chemistry
• Atmospheric chemistry

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:14957
• etdadmin_upload_710832

Keyword

• Sum frequency generation (SFG) spectroscopy
• Organic synthesis
• Cloud condensation nuclei (CCN)
• Alpha-pinene
• Beta-caryophyllene
• Secondary Organic Aerosol

Date created

• 2019-01-01

Resource type

• Dissertation

Rights statement

• In Copyright