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Cloud Condensation Nuclei Counter
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With Single (CCN-100) or Dual (CCN-200) Growth Columns
Clouds are a key factor in moderating climate change. Cloud condensation nuclei (CCN) are those aerosol particles that can form into cloud droplets, and an understanding of CCN concentrations in space and time is necessary if models are to accurately predict the magnitude of global climate change. The DMT CCN counter measures the concentration of these particles and can be operated on the ground or on aircraft. The DMT CCN counter is being used in laboratories to measure how different materials form cloud droplets, in urban environments to study how pollution affects cloud and precipitation formation, and in weather modification studies to determine when and where to seed clouds. This popular instrument comes equipped with single (CCN-100) or dual (CCN-200) columns for extended versatility.
Photo: Clouds near Salina Cruz, Mexico.
Photo by Darrel Baumgardner. |
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Advantages:
Measures the spectrum of cloud condensation nuclei (CCN) concentration as a function of supersaturation continuously using uninterrupted flow and a multichannel, optical particle counter that measures the size of the activated droplets
Features supersaturation as low as 0.07% and as high as 2%
Offers complete automation of up to 250 programmable and scanned supersaturation settings
Minimizes size and buoyancy effects with cylindrical geometry
Features onboard computer for control and data logging
Provides fast response and continuous flow, which allows airborne as well as ground-based applications
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Applications:
Atmospheric research
Climate change studies
Pollution research
Weather modification
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Photo: The CCN (inset) at a research station in Barrow, Alaska (main photo). Photos by Robert Albee, NOAA Earth System Research Laboratory.
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Principle of Operation:
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The CCN Counter is a continuous-flow thermal-gradient diffusion chamber for measuring aerosols that can act as cloud condensation nuclei. The CCN-100 draws an aerosol sample into 50-cm tall column, while the CCN-200 features two identical such columns. Inside the column(s), a thermodynamically unstable, supersaturated water vapor condition is created by taking advantage of the difference in diffusion rates between water vapor and heat. Water vapor diffuses from the warm, wet column walls toward the centerline at a faster rate than the heat. The wall temperature along the column gradually increases to create a well-controlled and quasi-uniform centerline supersaturation. Through software controls, the user can modify the temperature gradient and flow rate to change supersaturations and obtain the CCN spectra.
In the figure at left, we show point C along the centerline where the diffusing heat originated higher on the column (red-line, point A) than
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the diffusing mass (blue line, point B). Assuming the water vapor is saturated at the column wall at all points and the temperature is greater at point B than at point A, the water vapor partial pressure is also greater at point B than at point A. The actual partial pressure of water vapor at point C is equal to the partial pressure of water vapor at point B. The temperature at point C is lower than at point B, however, which means that there is more water vapor (corresponding to the saturation vapor pressure at point B) than thermodynamically allowed.
Seeking equilibrium, the supersaturated water vapor condenses on the cloud condensation nuclei in the sample air to form droplets, just as cloud drops form in the atmosphere. An Optical Particle Counter (OPC) using side-scattering technology counts and sizes the activated droplets.
Calibration:
DMT recommends periodically calibrating the CCN Counter supersaturation rate, flow sensors, pressure transducers, and the optical particle counter. The user can calibrate the supersaturation rate themselves by comparing the instrument’s output to that of reference instruments Differential Mobility Analyzer (DMA) and a CN Counter. A complete cleaning and calibration is also available from DMT.
The supersaturation rate is calibrated annually using a DMA and CN Counter.
The flow sensors are calibrated monthly using a flow meter and soap bubble unit/automated system.
The OPC is calibrated annually using DMT aerosol generator and 2.0 µm polystyrene latex (PSL) particles.
Once the calibration analysis is complete, the user can easily adjust the instrument by entering new values into the CCN software.
Software:
The CCN comes with a software program that provides a user-friendly virtual instrument panel for the control, data display, and data logging of the CCN instrument. For instance, the program enables the user to do the following tasks:
Collect data
Change supersaturation settings
Adjust temperature and air flow settings
Manipulate instrument pumps (e.g., turn air pumps on high to prevent condensation)
Quickly detect any operational problems
Update instrument calibration parameters
Adjust the instrument to prepare it for shipping or re-humidify it after shipping
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Information gathered during sampling sessions is written to output files that can be viewed in real-time and played back later for detailed analysis.
The software also regulates the instrument to prevent hardware damage due to factors such as excessive temperature, leaks, and laser problems.
In addition to the standard software, the CCN Counter interfaces with DMT's Particle Analysis and Display System (PADS). PADS allows the user to analyze data collected from the CCN Counter and other DMT instruments simultaneously, but does not allow control of the CCN Counter.
Specifications:
| Technique |
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Activation of CCN particles at constant supersaturation maintained in a 50-cm-high column with continuously wetted walls and a longitudinal thermal gradient; sizing of the activated droplets using an optical particle counter
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| Aerosol Medium |
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Air, 5 - 40 °C (41 - 104°F)
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| Number Concentration Range |
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Depends on supersaturation:
• 6,000 particles/sec at supersaturations below 0.2%
• 20,000 particles/sec at supersaturations above 0.3%
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Measured Particle Size Range
(from OPC, after supersaturation)
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0.75 – 10 µm
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Number of Particle Size Bins
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20
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Sampling Frequency
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1 Hz / 1 Second
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Supersaturation Range
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0.07 – 2.0%
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Time Required for
Supersaturation Change
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~30 seconds for 0.2% change
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Maximum number of automatically scanned supersaturation settings
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250
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Optical Particle Counter Laser
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660 nm, 35 mW
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| Flow Range |
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• Total flow: 200 – 1000 vol. cc/min (factory calibrated at 500 Vccm)
• Sample flow: 20 – 100 Vccm
• Sheath flow: 180 – 900 Vccm
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| Flow Control |
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• Total flow is adjustable from within CCN Counter software
• Sample/Sheath flow ratio is adjustable using manual metering valve
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| Pump |
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Solenoid pumps for water; diaphragm pump for air
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| Routine Maintenance |
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Every Four Days/Before Every Flight
• Empty and refill water bottles
• Check OPC water trap and bottom of case for water leakage
Monthly:
• Check air inlet filters
• Check flow calibration
• Check desiccant tube
Every Three Months:
• Replace airflow filter
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| Recommended Service |
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Annual cleaning and calibration at DMT service facility
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| Front Panel Display |
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Computer monitor, water supply bottle
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| Side Panel Connections |
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• System power switch
• LED for overall system power
• Watchdog light
• Air vents
• Inlet and exhaust valves
• +28 VDC pin connector
• Ethernet connection
• USB connection
• Mouse and keyboard connections
• Touchscreen connection
• Video connection
• Serial data port
• LED power connection
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| Computer System |
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On-board Intel® Celeron® 1 GHz processor
512 MB RAM
80 GB hard drive for data storage
User interface via standard keyboard and monitor (included)
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| Software |
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• CCN Counter Software, Playback Software
• Optional Particle Analysis and Display System (PADS) to record data in an aircraft system (Not required to operate the instrument; PADS requires an external computer, which is not included)
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| Data System Interface |
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RS-232, 9.6 Kb/sec Baud Rate (single CCN Counter) or 57.6 Kb/sec (Dual CCN Counter)
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| Data System Features |
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• Onboard computer for control and data logging
• Touch screen control and display
• Serial data output for external computer
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| Calibration |
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Comparison of CCN Counter output to reference instruments (Differential Mobility Analyzer (DMA) and a CN Counter
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| Features for Easy Aircraft Mounting |
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• Rack-mount compatible
• Center of gravity located 15.5” from bottom of back base plate
• Instrument plumbing system sealed for operation on pressurized aircraft
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| Power Requirements |
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28 VDC
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| Current |
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CCN-100:
15 A at startup, nominal 7 A during regular operation
CCN-200:
25 A at startup, nominal 20 A during regular operation
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| Shipping Container |
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Durable Atlas Case Corporation ATA Transit Case that conforms to the Air Transport Association’s Specification 300 Category 1 standards
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| Size (for both CCN-100 and 200) |
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For lab use (with frame):
• 35.0” H x 19.3” W x 15.6” D /
• 88.9 cm H x 48.9 cm W x 39.7 cm D
For aircraft use (without frame):
• 32.0”H x 15.25” W x 10.6 D /
• 81.3 cm H x 38.7 cm W x 27 cm D
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| Weight (CCN-100) |
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CCN-100:
• For lab use (with frame): 35.2 kg / 77.5 lb
• For aircraft use (without frame): 29.0 kg / 64.0 lb
CCN-200:
• For lab use (with frame): 50 kg / 110 lb
• For aircraft use (without frame): 43.8 kg / 96.5 lb
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Environmental Operating Conditions:
Temp
RH
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5 – 40°C (41 – 104 °F)
0 – 100% RH non-condensing
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Specifications are subject to change without notice.
Accessories:
Kits for consumable and spare parts, including the following for the CCN-200:
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Ship Kit
- Consumables Kit
- Field Repair Kit
Airborne CCN inlet assembly kit:
CCN rail mount
CCN aircraft inlet
Constant pressure inlet
How to Order:
For more information or to obtain a sales quote, contact DMT at +1.303.440.5576,
This e-mail address is being protected from spambots. You need JavaScript enabled to view it
. Please specify single or dual growth columns when ordering.
Acknowledgments:
The Cloud Condensation Nuclei (CCN) Counter is based on the design of Dr. Greg Roberts of Scripps Institute of Oceanography and Dr. Athanasios Nenes of the Georgia Institute of Technology. The patent for their design is licensed exclusively to DMT, patent number 7,656,510.
Selected Bibliography:
The following papers provide a representative sample of research conducted with the DMT CCN Counter. For a comprehensive bibliography of CCN-related publications, click
here.
Asa-Awuku, A., Engelhart, G. J., Lee, B. H., Pandis, S. N., and Nenes, A. (2009)
"Relating CCN activity, volatility, and droplet growth kinetics of β-caryophyllene secondary organic aerosol," Atmos. Chem. Phys., 9, 795-812.
Full text (1.5 MB pdf).
Koehler, K. A., S. M. Kreidenweis, P. J. DeMott, M. D. Petters, A. J. Prenni, and C. M. Carrico (2009), "Hygroscopicity and cloud droplet activation of mineral dust aerosol," Geophys. Res. Lett., 36, L08805, doi:10.1029/2009GL037348.
Abstract.
Lance, S., et al. (2009), "Cloud condensation nuclei activity, closure, and droplet growth kinetics of Houston aerosol during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS)," Journal of Geophysical Research, 114, D00F15, doi:10.1029/2008JD011699. Abstract.
Padró, L., D. Tkacik et al. “Investigation of Cloud Condensation Nuclei Properties and Droplet Growth Kinetics of Water-Soluble Aerosol Fraction in Mexico City.” Journal of Geophysical Research, 115: D09204, 2010. Abstract.
Roberts, G., and Nenes, A. (2005) “A Continuous-Flow Streamwise Thermal-Gradient CCN Chamber for Atmospheric Measurements,” Aerosol Science and Technology, 39, 206–221, oi:10.1080/027868290913988. Abstract or Full text (1.5 MB pdf, not available on all browsers).
Snider, J.R., H. Wex et al. “Intercomparison of Cloud Condensation Nuclei and Hygroscopic Fraction Measurements: Coated Soot Particles Investigated During the LACIS Experiment in November (LExNo) Campaign.” Journal of Geophysical Research, 115: D11205, 2010. Abstract.
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