1. Photoacoustic Measurements of Aerosol Light Absorption Aloft
W. Patrick Arnott, Desert Research Institute, University of Nevada, Reno NV
Objectives:
Quantify aerosol light absorption aloft at 676 nm.
Background:
Aerosol light absorption measurements have traditionally been accomplished using filter-based methods that are adequately sensitive, but are difficult to calibrate. Photoacoustic measurements can be calibrated with primary gas standard methods, and are much less sensitive to interference from light scattering aerosol than are filter methods.
Significance:
The noise and vibration environment on an aircraft challenge the ability to make measurements of sound pressure levels as low as 10-6 mb as needed for providing useful information on aerosol light absorption aloft. Aerosol light absorption is a key parameter in quantifying the effects of aerosols on climate.

2. Photoacoustic Measurements of Aerosol Light Absorption at 676 nm from the Twin Otter Aircraft
This is an image of the instument installed on the CIRPAS Twin Otter aircraft. The photoacoustic resonantor is housed in the enclosure immediately below the laptop computer used for data acquisition. The sample inlet is the tube on the upper left (behind the white tubing).

3. Pancakes Layers of Asian Smoke from the Air 27 May 3 (Photo by Roy the Co-pilot)
Photo courtesy of the CoPilot, Roy, on the aircraft.

4. May 27th: Layers Aloft Aerosol Light Absorption at 660 nm and 676 nm
Photoacoustic measurements are shown in black, PSAP filter based measurements are shown in red. Past efforts have largely used the PSAP for quantifying aerosol light absorption aloft. This figure illustrates general agreement of the two methods for the interesting layer case shown on the previous slide. The aircraft was in the layers during times that correspond to the relative maxima of light absorption. Here we have quantifed the light absorption at 676 nm by the photoacoustic method; this relates to layer lofting and dynamics through radiative heating.