(682c) Size-Resolved Scanning Flow CCN Analysis (SFCA): A Method for Fast Measurements of CCN Spectra

The Continuous-Flow Streamwise Thermal-Gradient Cloud Condensation Nuclei Counter (CFSTGC) is rapidly becoming the instrument of choice for both laboratory and field measurements of cloud condensation nuclei (CCN). Typically, the instrument is operated at a constant flow rate, and supersaturation is adjusted by changing the column temperature difference, which is relatively slow (20-40 seconds for the column temperatures to stabilize and as much as 3 minutes for the OPC temperature to stabilize) and may introduce particle volatilization biases¹. Data collected during transient periods are often discarded, which is particularly problematic for aircraft measurements in heterogeneous environments. We present a new mode of operation, termed ?Scanning Flow CCN Analysis? (SFCA), in which the flow rate is changed over time in the flow chamber, while maintaining a constant temperature gradient; this causes supersaturation to continuously change, allowing the measurement of a CCN supersaturation spectrum much more quickly over timescales relevant for airborne measurements (~10-60 seconds and potentially even less) and without loss of data continuity. We present results of size-resolved CCN spectra obtained using SFCA, coupled with an electrostatic classifier to demonstrate the application of the technique to ambient measurements of urban aerosol.

¹Asa-Awuku, A., et al., Atmos. Chem. Phys., 9, 2009.