Thursday, March 11, 2010

A Comparison of Measured and Predicted Cloud Condensation Nuclei (CCN) Concentrations

I presented my research on Tuesday at the University of North Dakota 2010 Scholarly Forum. Although a lot has changed from the original abstract I still provide it here for the curious. (Follow the links to access the PDF slides and the code and data.) Once I achieve the closure on the lab data I should be able to easily extend the similar methodology onto our field data.


    Research on CCN helps us to understand cloud and precipitation formation in a local scale and resolving the indirect aerosol effects on a global perspective. Following the conclusions of similar studies which emphasize the particle size distribution's being the biggest impactor on cloud nucleation ability of aerosols, and accounting for the chemical composition with the hygroscopicity parameter in κ-Köhler theory, a CCN closure study was performed. Measurements of the aerosol size distributions in the range of 0.1 to 3 μm is made by using a Passive Cavity Aerosol Spectrometer Probe (PCASP-100X), and the missing 0.01 to 0.1 μm range data is extrapolated with a spline interpolation technique. A two-parameter log-normal distribution is also estimated by fitting on the aerosol measurements including total aerosol particle concentrations measured by a Condensation Particle Counter (CPC - TSI-3771). Determination of the critical activation diameters is done by utilizing the κ-Köhler theory as proposed by Petters and Kreidenweis (2007). The closure resulted with the best R2=0.33 between the predicted and measured CCN concentrations at the 0.2% supersaturation (SS). Additional to this poor agreement, the concentrations obtained from the calculations under-predict the CCN concentrations over the full range of supersaturation measurements. The ground and airborne data from the spring 2009 Saudi Arabia field campaign are currently being analyzed.

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