Lund University / CAST 2010 Why SFCA? Scanning Flow CCN Analysis Cerina, Staffan, Göran & Birgitta Original developers: Rich Moore & Nenes Rapid & Continuous Measurement of Supersaturation spectra Express Timescales (Airborne measurements, chamber - ageing) Small Samples for Analysis As good as Stepping-ΔT-Mode? Colder than usually (no heating of aerosol required) – less volatility losses

Lund University / CAST 2010 Why? Saving time – before it took a while to stabilize the temperature, with SFCA the flow is changed fast How? Results? How does the traditional Stepping-ΔT-Mode (CFSTGC) work…? …compared with how the SFCA works? Calibration, Brocken longterm

Lund University / CAST 2010 This is how the CFSTGC works… Diffusion of heat in air (N 2 O 2 ) is slower than diffusion of water vapor The partial pressure of water vapor at center (C) is equal to point B. However, the temperature is equal to point A – hence there is more water vapor than thermodynamically allowed and supersaturation is generated

Lund University / CAST 2010 Higher flow will increase the difference between the partial pressure of water vapor & temperature, and thereby increase the supersaturation …and the SFCA

Lund University / CAST 2010 Results - Calibration

Lund University / CAST 2010 Results - Calibration

Lund University / CAST 2010 Comparison with data from Rich (similar testruns 6K/120s/20s)

Lund University / CAST 2010 Double charged FIG. 6c. Zoom-in on double charged particles for 120 s flowscan for laboratory-generated, 70 nm ammonium sulfate aerosol at P ∼ 1010 mb and ∆Tnom = 6 K.

Lund University / CAST 2010 Results – Brocken 1142 m

Lund University / CAST 2010 Results – Cloud on Brocken 1142 m Steam train time table arrival 12:51 departure 13:14

Lund University / CAST 2010 Following the aerosol particle through the column (10-20 s) (using CFTGC vs. SFCA) CFSTGC Axial Distance From Inlet SS [%]Temp [ o C] Flow [cm 3 min -1 ] SFCA SS [%] Axial Distance From Inlet Temp [ o C]Flow [cm 3 min -1 ]

Lund University / CAST 2010 Problems encountered? Down scan – low SS - the drops can be too few and too small for the OPC detection limit Water level to low? Nenes: ”…is some channeling in the ceramic bisque lining (perhaps some cracking from prolonged use). Also, double-check that the OPC is clean.”

Lund University / CAST 2010 Outlook Cooperation with Rich Moore and Nenes? – fast scans article Brocken data Chamber measurements Vavihill or new ICOS site

Lund University / CAST 2010 Conclusion Better time resolution, more appropriate for atmospheric conditions Reliable, but maybe more service (pump)? Not fully understood