Exploration of the short-wavelength optical properties of particles using broadband optical cavity spectroscopy

This presentation describes spectroscopic measurements of atmospherically revelant trace gases and aerosols using incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS). Although the combination of optical cavities with broadband light sources is now an established approach for sensitive measurements of absorbing atmospheric gases, only recently has the same method been applied to the study of aerosol optical properties. An advantage of the IBBCEAS technique is that it can use light sources with attractive properties, whether in terms of size and cost (light-emitting diodes, LEDs), or broad spectral coverage and output at ultraviolet wavelengths (xenon arc lamps). My presentation will focus on our recent progress in developing IBBCEAS for measuring extinction spectra of particles from 320 to 450 nm. This spectral region is important because many atmospheric aerosols show increasing absorption at shorter wavelengths, but the near-ultraviolet has been little explored owing to the lack of practical lasers and high power LEDs in this region. The method, calibration, stability, and other performance characteristics will be described in detail. Results from experiments forming secondary organic aerosol (SOA) in atmospheric simulation chamber studies and from field observations will be reported. Finally, the future outlook for the approach and its application in atmospheric observations will be discussed.