Lund University / CAST 2010

Why SFCA?Scanning Flow CCN Analysis

Cerina, Staffan, Göran & BirgittaOriginal 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

(N2 O2) 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 ammoniumsulfate 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 mSteam train time table arrival 12:51 departure 13:14

0 0.1 0.2 0.3 0.4 0.5 0.60

50

100

150

200

250

12:45:59

12:50:40

12:55:20

13:09:20

13:14:00

13:23:19

Supersaturation (%)

CCN

num

ber c

once

ntra

tion

(cm

-3)

Lund University / CAST 2010

Following the aerosol particle through the column (10-20 s)

(using CFTGC vs. SFCA)CFSTGC

Axi

al D

ista

nce

From

Inle

t

SS [%] Temp [oC] Flow [cm3min-1]

0.0

0.5

SFCA

SS [%]Axi

al D

ista

nce

From

Inle

t

Temp [oC] Flow [cm3min-1]0.5

0.0

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