Evaluation Product : Average of Cloud Condensation Nuclei from AOS
General Description
This VAP was developed to consolidate the relevant CCN parameters into a single file and average the data over the 5-minute integration time of each percent super saturation (%ss) value. The surface sites measure the CCN concentration at several super saturations using a DMT single-column CCN counter (Roberts and Nenes, 2005). The percent super saturation of the instrument is stepped through 7 intervals every 30 minutes with 5 minutes at each setting in a pyramid profile. The first minute after a change in %ss, the CCN temperatures are unstable and the %ss value usually overshoots the set point value. For this reason the first minute of every %ss setting is disregarded and only the last four minutes are averaged together.
The %ss in the CCN data stream is calculated using a heat transfer and fluid dynamics model flow model (Lance et al., 2006). The model uses the calibrated temperature, pressure and flows in the instrument to calculate the %ss. Small variations in the %ss will arise from changes in the column thermal properties in the instrument. Rose et al. (2008) discusses the model and salt calibration calculations of the instrument %ss and uncertainty associated with thermal properties. The calculated %ss value was chosen to be more reliable than the static calibration obtained via salt aerosol because the %ss value changes dynamically with the instrument flow, pressure and room temperature, and because salt calibrations are inconvenient at remote locations so happen infrequently.
Data Information
Contacts
Principal Investigator
Connor Flynn (509) 375-2041
