Principle of Operation
How to Order
Sheath Filter Testing & Replacement (128 KB)
CCN-100 Manual (5 MB) or CCN-200 Manual (7 MB)
Print Version (600 KB)
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: The CCN (inset) at a research station in Barrow, Alaska (main photo).
Photos by Robert Albee, NOAA Earth System Research Laboratory.
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 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.
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.
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:
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.
|Technique||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|
|Aerosol Medium||Air, 5 - 40 °C (41 - 104°F)|
|Number Concentration Range||
Depends on supersaturation:
|Measured Particle Size Range (from OPC, after supersaturation)||0.75 – 10 µm|
|Number of Particle Size Bins||20|
|Sampling Frequency||1 Hz / 1 Second|
|Supersaturation Range||0.07% - 2.0%|
|Time Required for Supersaturation Change||~30 seconds for 0.2% change|
|Maximum Number of Automatically Scanned Supersaturation Settings||250|
|Optical Particle Counter Laser||660 nm, 35 mW|
|Pump||Solenoid pumps for water; diaphragm pump for air|
Every Four Days/Before Every Flight
Every Three Months:
|Recommended Service||Annual cleaning and calibration at DMT service facility|
|Front Panel Display||Computer monitor, water supply bottle|
|Side Panel Connections||
|Data System Interface||RS-232, 9.6 Kb/sec Baud Rate (single CCN Counter) or 57.6 Kb/sec (Dual CCN Counter)|
|Data System Features||
|Calibration||Comparison of CCN Counter output to reference instruments (Differential Mobility Analyzer (DMA) and a CN Counter|
|Features for Easy Aircraft Mounting||
|Power Requirements||28 VDC|
|Shipping Container||Durable Atlas Case Corporation ATA Transit Case that conforms to the Air Transport Association’s Specification 300 Category 1 standards|
|Size (for both CCN-100 and 200)||
For lab use (with frame):
For aircraft use (without frame):
|Environmental Operating Conditions||
Temperature: 5 – 40°C (41 – 104 °F)
RH: 0 – 100% RH non-condensing
Specifications are subject to change without notice.
Kits for consumable and spare parts, including the following for the CCN-200:
Airborne CCN inlet assembly kit:
Please specify single or dual growth columns when ordering.
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.
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.