SP2

Colorado: SP2 Deployment at StormVEx

15 November 2010 - 25 April 2011

Lead Scientist: Arthur Sedlacek

Observatory: OSC, SBS

How does the boundary layer influence BC encapsulation? Is there a correlation between BC loading and precipitation? And if so, what is the correlation between BC age with precipitation washout? These scientific questions are part of our community's larger research effort to better understand cloud-aerosol interactions in mixed and ice-phase clouds and how these interactions affect climate change. However, the extremely low BC number densities present at the Storm Peak Laboratory have confounded previous attempts to measure BC absorption or required signal averaging measured in days (Mazzoleni 2009). In an effort to get at the rich, and as yet untapped, data set that is present at Storm Peak Lab, the SP2 (single particle Soot Photometer) was deployed at two sites during the STORMVEX (Storm Peak Lab Validation Experiment) campaign. The SP2 measured the mass on individual BC particles through laser-induced incandescence thereby providing data on BC loading (#/m3 and ng/m3), size distribution (nominally 80 – 600 nm: mass equivalent diameter) and fresh versus aged soot (via coating thickness). One of the unique aspects of the STORMVEX campaign is that the chosen deployment sites provided the opportunity to examine boundary layer processing of BC. Specifically, deployment of both ARM SP2s, one within the AMF2-AOS platform located at Christie Peak (~2500 m) and the other at Storm Peak Laboratory (~3200 m), provided BC measurements in the free troposphere (SPL site) and in/below the boundary layer. Updraft conditions provided the opportunity for both SP2 instruments to sample the same air mass and, using the Leading Edge Optimization technique (Gao et al. 2007), extract BC coating information – fresh soot possessing negligible coating whereas aged BC is characterized by a thick coating of organic/inorganic. STORMVEX also provided the equally unique opportunity to examine what correlation(s) exists between BC age and precipitation washout. Since fresh soot is known to be hydrophobic and aged soot hydrophilic, it is reasonable to expect that aged BC would be more efficiently washed out during a precipitation episode by serving as IN/CCN. By looking for correlations of coating thickness estimates with washout, we can begin to answer this type of question. Admittedly, while STORMVEX is a winter campaign and provided ample opportunity to examine the correlation between BC age and mixed and ice-phase clouds, the measurement campaign lasted into the late April, thus providing similar opportunities to ask the same question with respect to wet precipitation. References: Gao, R. S. J. P. Schwarz, K. K. Kelly, D. W. Fahey, L. A. Watts, T. L. Thompson, J.R. Spackman, J. G. Slowik, E. S. Cross, J. –H. Han, P. Davidovits, T. B. Onasch, and D. R. Worsnop, (2007) A Novel Method for Estimate Light-Scattering Properties of Soot Aerosols Using a Modified Single-Particle Soot Photometer, Aerosol Sci. Tech. 41:125-135. Mazzoleni, C. (private communication, 2009)