Development of spectroscopic methods for the characterization of organic aerosols

Atmospheric aerosols have been found to impact not only visibility and climate, but also human health. Characterization of the composition and chemistry of tropospheric aerosols, which are generated by a variety of sources and are often a complex mixture of species including inorganic ions, trace metals and organic compounds with a range of volatilities, is one of the many challenges faced by today's aerosol scientist. Information about what is in and on ambient aerosols, as well as the atmospheric processing of these compounds, is becoming increasingly important as particle concentrations are implicated in increased mortality levels of individuals with pulmonary and cardiac diseases. The organic fraction, which may play a critical role in the toxicological impact of these aerosols, is often the most challenging to characterize because of the range of volatilities of the species present.; The goal of this project is to develop spectroscopic methods capable of analyzing the composition of organic aerosols without disturbing the delicate gas-particle equilibrium established by semi-volatile components. The methods investigated include the combination of continuous heating with conventional scan Fourier transform infrared (FT-IR) spectroscopy, pulsed-heating with step-scan FT-IR (S2FT-IR) spectroscopy and pulsed-heating with visible ultraviolet (VUV) ionization and time-of flight mass spectrometry (TOFMS). Results from the analysis of aerosols by continuous heating and conventional FT-IR indicate this method is capable of providing quantitative information about the composition of multi-component organic aerosols in high-load environments. The time-resolution of the S2-FT-IR approach combined with visible light scattering methods provides insight into the processes involved in pulsed-heating including aerosol shattering, vapor plume formation, in addition to temporal profiles of the vapor plume and particle size. Compositional analysis of organic aerosols reacting with gas-phase species in a flow tube is accomplished by the combination of pulsed-heating and VUV-TOFMS. Results from studies of the heterogeneous reaction of ozone with oleic acid particles show that this reaction occurs on time scales relevant to the lifetime of ambient particles. Each method presented provides a unique contribution to the characterization of organic aerosols.