Purdue University Graduate School
Kyla Siemens dissertation (FINAL).pdf (14.71 MB)

Molecular Characterization of Light-Absorbing Components in Atmospheric Organic Aerosol

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posted on 2024-04-17, 15:28 authored by Kyla Sue Anne SiemensKyla Sue Anne Siemens

Atmospheric organic aerosols (OA) have diverse compositions and undergo complex reactions and transformations within the atmosphere, leading to profound impacts on air quality, climate, and atmospheric chemistry. In particular, these aerosols play an important role in Earth's effective radiative forcing (ERF) through interactions with solar radiation, absorbing and scattering sunlight and terrestrial radiation. These interactions result in a warming and cooling effect on the climate, respectively. This dissertation seeks to unravel the intricate molecular characteristics of atmospheric OA, focusing specifically on its light-absorbing components, known as ‘Brown Carbon’ (BrC), and aims to comprehend its dynamic interplay within the atmosphere. The research employs state-of-the-art multi-modal mass spectrometry techniques to investigate atmospheric OA derived from the combustion of fossil fuels and biomass burning. Through a combination of controlled laboratory experiments and real-world sample analyses, these works provide molecular-level insights crucial for source apportionment and predictive modeling of OA fate. Chapter 2 details the instrumentation and data analysis methods, laying a robust foundation for subsequent chapters.

Chapter 3 delves into the investigation of smoldering-phase biomass burning organic aerosols (BBOA) and introduces an innovative fractionation method for high-level molecular characterization, targeted to streamline source apportionment of BBOA. This chapter also presents an extensive assessment of particle-to-gas partitioning of BBOA, providing valuable information for modeling atmospheric lifetimes and fate. In Chapter 4, a comparative analysis of BBOA from wild and agricultural fires is conducted, employing advanced molecular characterization techniques. Chapter 5 showcases the synergistic use of multi-modal mass spectrometry techniques to probe the chemical evolution of individual BBOA components. Finally, Chapter 6 examines the molecular analysis of secondary OA (SOA) generated from the photooxidation of a fossil-fuel proxy.

The comprehensive molecular-level studies presented contribute essential insights for climate modeling, aiding in resolving uncertainties associated with OA's impact on global ERF. The research not only challenges existing analytical methods but also introduces novel approaches for obtaining relevant information about atmospheric OA components. Overall, this work advances our understanding of the intricate dynamics of atmospheric aerosols, facilitating more accurate climate predictions and addressing uncertainties surrounding their net radiative impact.


NSF Grant no. AGS-2039985

BSF Grant no. 2020656

U.S. Department of Energy Atmospheric System Research Program, Office of Biological and Environmental Research (Grant DESC0018948)

U.S. Department of Energy, Office of Biological and Environmental Research, Atmospheric System Research program Grant no. DESC0021977


Degree Type

  • Doctor of Philosophy


  • Chemistry

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Alexander Laskin

Additional Committee Member 2

Hilkka Kenttamaa

Additional Committee Member 3

Lyudmila Slipchenko

Additional Committee Member 4

Sergey Nizkorodov