AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
UV-Visible Photoacoustic Spectroscopy for Aerosol Absorption
AL FISCHER, Geoffrey Smith, University of Georgia
Abstract Number: 550 Working Group: Instrumentation and Methods
Abstract Atmospheric aerosols directly affect climate by absorbing and scattering sunlight, leading to warming and cooling effects, respectively. After CO2, absorbing carbonaceous aerosols are thought to be one of the largest contributors to warming of Earth. However, the exact magnitude of this effect remains one of the largest uncertainties in climate predictions. Although many methods exist for measuring aerosol absorption, they often suffer from artifacts and drawbacks. For example, many rely on impinging aerosols on a filter prior to measurement, which may inherently alter the aerosols and change their optical properties or lead to a need for filter-based correction factors that must be measured empirically; alternatively, techniques not relying on filter collection, such as photoacoustic spectroscopy, are often limited in their wavelength coverage. Direct, in-situ, wavelength-resolved measurements of aerosol absorption have been difficult to achieve. We have constructed two photoacoustic instruments designed to be used in tandem. Together, they cover 7 wavelengths from the UV (320 nm) to the near-IR (785 nm) to provide wavelength coverage similar to many filter-based techniques (e.g. aethalometry). Each instrument consists of either 3 or 4 diode lasers coupled into a single multipass photoacoustic cell. Extra care has been taken to keep the instruments compact and robust while maintaining exceptional detection limits (<1 Mm-1). This has created a portable photoacoustic system capable of measuring absorption by ambient aerosols in even the cleanest of environments. The construction, calibration, and early applications to ambient aerosols will be presented.