# Cloud Droplet Analyzer (CDA) from Palas - S2noCliME Dataset ## General Information Institution: Storm Peak Laboratory (SPL), University of Utah SPL Director: Prof. Gannet Hallar Principal Investigators: Prof. Claire Pettersen, Prof. Jay Mace, Prof. Lynn McMurdie, Prof. Angela Rowe Authors: A. Gannet Hallar, Annegret J. Lang, Ian McCubbin, Joseph Bail Contact: Gannet.Hallar@utah.edu Data Collection: 2025/02/20 - 2025/04/06 Location: Storm Peak Laboratory on Mt. Werner (3220 m M.S.L.; 40.455N, -106.744W) Key words: Cloud Micro-physics, Cloud Droplet Measurements, Cloud Droplet Analyzer, Palas, Number Concentration, Mass Concentration, Orographic Clouds Funding: Field Campaign Support through NSF award # 2348449 Format: .csv Date: 2026/06/03 Time Zone: Mountain Standard Time (MST: UTC-07:00) ## Data Description The Cloud Droplet Analyzer (CDA) from Palas was deployed as part of the Snow Sensitivity to Clouds in a Mountain Environment (S2noCliME) field campaign at Storm Peak Laboratory. The instrument was external on the top deck of the laboratory. A heated inlet was provided by Palas for the instrument. The CDA data in this directory were exported from the Palas software PDAnalyze. The combined CDA dataset is provided in long format. Each timestamp appears once for each retained diameter bin (75 rows per timestamp). The timestamp represents the end of the CDA measurement interval, and each row summarizes the approximately 120 seconds prior to that timestamp. The following CDA combined file is provided: `combined_cda_clean.csv`: velocity-screened CDA dataset with timesteps removed when `sensor_particle_velocity_m_s` was outside the range 60 to 68 m/s, excluding the largest two size bins that overcount particles (based on information by the manufacturer). ## PDAnalyze Software Specifications (Software Version: 2.039) The following specifications were selected in the software before exporting the data: number of intervals per decade: 32 density: 1000 kg/m3 form factor: 1 dilution: 1 refractive index: 1.33+0i (water) ## File Structure The source files are exported from the software as three different file types: scalar files, size-distribution statistics files, and operations files The scalar files contain the Palas scalar microphysical quantities: - `Cn [P/cm^3]` - `Cm [mg/m^3]` - `M,3,2 [µm]` The statistics files contain bin-resolved differential number concentration. The bin metadata rows are interpreted as: - lower diameter bin edge - arithmetic bin midpoint - upper diameter bin edge The operations files contain instrument operation variables that are merged into the combined dataset by timestamp: - `in sensor particle velocity u [m/s]` - `pump performance [%]` - `LED temperature [°C]` - `flow rate [l/min]` The columns in the final CDA file contain the scalar data, statistical data and operations data, as well as some calculated quantities: - `timestamp_mst` - `interval_duration_s` - `stats_relative_time_s` - `operation_relative_time_s` - `bin_index` - `lower_diameter_bin_edge_um` - `midpoint_diameter_um` - `upper_diameter_bin_edge_um` - `dlogDp` - `dCn_palas_retained_bins_P_cm3` - `dCn_dlogDp_from_retained_bins_P_cm3` - `total_Cn_palas_P_cm3` - `Cm_palas_mg_m3` - `sauter_mean_diameter_palas_um` - `total_Cn_from_retained_bins_P_cm3` - `Cm_from_retained_bins_mg_m3` - `sauter_mean_diameter_from_retained_bins_um` - `sensor_particle_velocity_m_s` - `pump_performance_percent` - `led_temperature_C` - `flow_rate_l_min` where "_retained_bins" indicates all variables that have been recalculated under exclusion of the largest two size bins, and "_palas" indicates the original values obtained from the software. ## Data Processing and Quality Data processing has been performed as follows: 1. The scalar, statistics, and operations files were read and combined into a single long-format CDA dataset. 2. The source files use local Mountain Time and include the daylight-saving transition on 2025/03/09. Timestamps are converted to MST with format `yyyy-mm-dd HH:MM:SS`. 3. The largest two original CDA size bins were removed in the final dataset, because the instrument software assigns unclassified particles to the largest available bins. The output retains 75 of the original 77 size bins. 4. Retained-bin scalar values were recalculated from the retained differential size distribution after excluding the largest two bins. 5. `dCn_dlogDp_from_retained_bins_P_cm3` was calculated as `dCn_palas_retained_bins_P_cm3 / dlogDp`. The retained-bin mass concentration assumes spherical particles with density 1000 kg/m^3. Basic quality control has been conducted as follows: 1. The largest two original CDA size bins were excluded from the combined files as described above. 2. Instrument operation variables were merged into the combined dataset for diagnostic checks: - The flow rate was found to be constant around 5 l/min, as expected. - The particle velocity was screened using the expected range 60 to 68 m/s as specified by the instrument manufacture. Timesteps with `sensor_particle_velocity_m_s` outside 60 to 68 m/s, or with missing velocity, were removed from the final dataset. This velocity screening removed 38.50% of the data. Thereby, most suspicious data periods were removed, but it should be noted that some short periods of suspicious data remain in the final dataset showing elevated number concentrations, especially when velocities were variable even though they were within the expected range. 3. Plots of available data were generated and visually inspected in combination with Mesowest 12 m wind data. Wind changes did not appear to negatively impact the measurements. The CDA was running continuously. Data that has been removed during processing can be requested from the point of contact. ### Known Issues & Additional Information * While periods with sensor particle velocity outside the specified range were removed, periods with variable sensor particle velocities within this range may still affect data quality. Therefore, the clean CDA file may still contain artifacts especially during intermittent data periods. Users should visually inspect relevant periods before analysis. * The statistics files contain interval-begin timestamps, while scalar and operations files align with interval end. This is accounted for in the processing of the present dataset but not in the raw data. * The largest two original CDA size bins were removed because they appeared problematic and influenced moment-derived quantities in the scalar output data (`total_Cn_palas_P_cm3`,`Cm_palas_mg_m3`,`sauter_mean_diameter_palas_um`). For total Cn, Palas and retained-bin values are generally similar; users should choose based on whether they want consistency with the retained size distribution. For Mass Concentration (Cm) and Sauter Mean Diameter (SMD), the "retained" values are likely more representative as they are not skewed by the particles that were added to the largest bins. * The recalculated retained-bin quantities differ from Palas scalar output because the Palas scalar values likely use all original bins, including the two largest bins removed here. * The smallest retained CDA bins remain in the dataset, but values for bins 1 through 9 are generally zero, likely because they are outside the instrument's detection limit. The first consistently nonzero bin is bin 10, with midpoint diameter about 0.778 µm. * Measurements below about 0.6-0.8 µm should be interpreted carefully because the instrument measurement range is reported by Palas on their website (https://www.palas.de/en/product/cda?save=accept) as follows: 0.6–40 µm, 0.8–100 µm. * The retained-bin scalar calculations use the Palas arithmetic bin midpoint. * Comparison of the CDA data with the DMT-Cloud Droplet Probe (CDP) showed that the overlap between clean CDA and clean CDP periods is limited relative to the full IOP duration. Time-resolution differences further complicate comparison, and discrepancies were observed in the limited overlapping period. * At the following timestamps, the differential number concentration values are missing for all retained bins, while the recalculated retained-bin total concentration and mass concentration are reported as 0.0. These timestamps should be treated as missing distribution data rather than confirmed zero-particle measurements: 2025-02-25 09:37:11 MST, 2025-02-25 15:37:10 MST, 2025-03-26 11:36:27 MST, 2025-03-28 11:54:11 MST ## Data Quality Notes & Caveats - This dataset is provided "as-is." While structural processing and basic quality control have been applied as described above, users are responsible for ensuring the data quality meets the requirements of their specific research applications. - The clean CDA dataset should be considered a screened dataset, not a fully validated final science product. - Moment-derived variables such as mass concentration and Sauter Mean Diameter are sensitive to large-particle bins and to assumptions about particle size, shape, and density.