AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Highly Size- and Time-Resolved Particulate Matter Characterized by Novel Optical Analysis
NICHOLAS SPADA, David Barnes, Shankar Chellam, Thomas A. Cahill, University of California, Davis
Abstract Number: 624 Working Group: Instrumentation and Methods
Abstract Aerosols may have a large impact on the atmospheric radiative balance by means of heating or cooling, both directly and indirectly. In spite of the myriad optical devices and techniques currently in use, aerosols have the greatest uncertainty in the global radiative budget by far. New techniques for studying their interactions with light radiation are necessary to increase comprehension of global climate change.
In response to this, a high-resolution technique for quantifying optical parameters of size- and time-resolved particulate matter (PM) samples was developed. Total extinction is directly measured while scattering is resolved from absorption via application of beta-attenuated mass measurements and calibrated mass scattering efficiencies. In this way, absorption in inverse megameters is achieved in eight size modes spanning 10 to 0.09 micrometers with up to one hour time resolution. The large number of wavelengths (n = 120, lambda = 350 – 800 nm) monitored enables precise determination of Angstrom exponents, which may be useful in identifying major aerosol types. Good correlations with a collocated Aethalometer provided validation of black carbon monitoring and were most correlated with the 0.26 – 0.09 micrometer size mode. The current products of this technique include size and time profiles for extinction, absorption, single-scattering albedo, and Angstrom exponents for both extinction and absorption. In this way, a comprehensive understanding of PM optical parameters can be collected expeditiously.
This technique was applied for specific studies targeting those with interesting optical profiles: namely the largest rail yard in the western United States, the petrochemical industrial area of the Houston ship channel, and a unique automotive tunnel restricted to single-axle vehicles. The optical results of these studies highlight the importance of concurrent size and time resolution while showcasing the elevated clarity of ambient pollution profiles. These results, including the system geometry and calibration results, will be presented.