Airborne in-situ measurements of cloud condensation nuclei during the HALO-AC3 campaign in March/April 2022

This data set contains in situ measurements of cloud condensation nuclei (CCN) during HALO-(AC)³ in March/April 2022. Using a miniature CCN counter (mCCNC; Roberts & Nenes, 2005) operated onboard research aircraft Polar 6 (P6), aerosol particles were sampled with either the P6's standard aerosol inlet (P6AI; Leaitch et al., 2016) or the counterflow virtual impactor (CVI; Ogren et al., 1985). Like other CCN counters, the mCCNC consists of a continous-flow thermal gradient diffusion chamber, in which a stream-wise temperature gradient is induced to achieve defined SS and corresponding particle activation to droplets (Roberts and Nenes, 2005). Activated particles are counted by an optical particle counter (OPC) behind the chamber. With this, CCN number concentration at a supersaturation of 0.088±0.002 % (arithmetic mean ± one standard deviation) was measured at a temporal resolution of 1 Hz. Data quality was assured by taking into account additional parameters measured inside the mCCNC to determine when the instrument was in its operational window. The operational window is defined as when the output current of the OPC was below 2400 mV, the internal pressure was within 5 % of 700 hPa, the sample flow was within 33 % of 150 mL/min, and the temperature difference between the ends of the measurement column (delta_T) was within 10 % of 3.9 K. When the instrument was within its operational window and when not is indicated by the data quality flag (quality_flag). At which of the two inlets the mCCNC was operated, is indicated by the inlet mode flag (inlet_mode). In order to address the time delay between particles entering the inlet system and reaching the mCCNC after passing through the sampling line, timestamps have been corrected by moving them 20 seconds backward in time. All CCN number concentration values are corrected to standard conditions (1013.0 hPa and 273.15 K).