Cloud Condensation Nuclei Concentration collected from CCN Counter at Barrow, Alaska during STUARD

Authors: Saha, S.; Russell, L.M.; Andrews, E.; Leaitch, R.W.

Contact: Sourita Saha. sosaha@ucsd.edu. Lynn Russell, lmrussell@ucsd.edu Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037. 

Cite data: Russell, Lynn M.; Saha, Sourita; Thomas, Bryan; Burgener, Ross; Andrews, Elizabeth; Thiemens, Mark H.; Quinn, Patricia; Upchurch, Lucia; Leaitch, W. Richard (2024).  Aerosol Measurements at Utqiagvik, Alaska, from 2022 to 2026 for Sustaining The Utqiagvik Aerosol Record of Decades (STUARD).  UC San Diego Library Digital Collections. https://doi.org/10.6075/J0W66KZF 

ABSTRACT: The CCN-100 counter  measures aerosol particles that can activate to form cloud droplets (also known as cloud condensation nuclei). The instrument operates by supersaturating sample air to the point where the CCN becomes detectable particles, which are then sized using an optical particle counter. The supersaturations set are 0.1%, 0.25%, 0.5%, 1%, and 1.5% at intervals of 5 minutes, and then the order is reversed and stepped back to 0.1%. In each hour supersaturations from 0.1% to 1% have 10 min sampling while 1.5% has only 5 min. 

SOFTWARE IMPLEMENTATION: The data analysis was done in MATLAB R2023a and Microsoft Excel.

Processing: For processing, , individual raw files were assembled. Only the data points that start on the minute (one-minute averages) were kept, removing other spurious data. The data was then filtered for only supersaturations corresponding to 0.1, 0.25, 0.5, 1, and 1.5% (discard other supersaturation values) and then assembled sequentially in time. 

The times of each scan may be longer in many cases because the instrument does not start counting at a particular supersaturation until it has stabilized. Exclude the first-minute average of each of the four higher supersaturation scans to ensure as much stabilization of the S as possible.  For each 0.1% supersaturation scan (10 minutes long), exclude the first three minutes because it can take longer to stabilize at 0.1%. In the “Instrument flags” column (column B) a value of “0” means the temperatures are not stabilized and a value of “1” means they are.  NOAA uses “10000000” to flag whenever a ‘0’ from the DMT file is included in the 60-second average.  As long as any data with S values that do not correspond to one of the five nominal values and the first-minute average (first three minutes in the case of 0.1%) are excluded, there should be no issues with temperature stabilization, unless there are other problems. Thus, the flags in column B in the CCN files can be ignored.  

There are two columns in the CCN raw file, 'Total concentration' and 'Total concentration without unstable data'. Discard the points when (CCN[without unstable data]-CCNtot)/CCNtot) isn't within 10%.  Plot the calculated supersaturations vs the measured temperature difference (T3-T1) and fit a line through it. Remove the points where calculated supersaturations do not agree within 2 standard deviations of each linear fit (to bring consistency to the supersaturation as a function of temperature difference, flow etc).  

Wind direction flags were applied to the CCN data to get information about the background conditions at Utqiagvik. 
The aforementioned steps have already been applied to the raw data to get the processed data. The user need not to apply these steps to the processed data.

Information about data file: Each xlsx file contains processed data for the entire month. 
1st column contains time information (give format)
2nd column contains the supersaturation (%)
3rd column contains the CCN concentration (per cc)