Supplementary material to "Effects of 20–100 nanometre particles on liquid clouds in the clean summertime Arctic"

S1. Instrument calibrations, evaluationsThe calibrations of the UCPC, SMS, UHSAS, CCN and FSSP100 were evaluated in the laboratory prior to integration on the aircraft and again with the instrumentation in the aircraft at Resolute Bay.The results of these evaluations are summarized below: a) In the laboratory, a Gilibrator was used to determine the relevant flow rates were within 5% of their expected values for the UCPC, SMS and UHSAS.Particle sizing was evaluated against nearly monodisperse 80 nm and 200 nm polystyrene latex spheres (PSLs) as well as nearly monodisperse 50 nm and 100 nm particles of ammonium sulfate (AS); the latter were generated from the atomization of solution droplets that were dried and subsequently size-selected with a TSI 3081 Electrostatic Classifier.The classifier output was also sampled with a TSI 3034 SMPS for comparison, which sized to within 2% of the nominal settings of the PSLs and the 3081.The peak sizes measured with the SMS ranged from 2% to 10% higher than the nominal sizes.The UHSAS was evaluated only with the nearly monodisperse AS particles, and its peak sizes were found to be 6%-8% below the nominal sizes.The number concentrations of both the SMS and UHSAS were evaluated against number concentrations measured with a TSI 3772 CPC, and the agreement was to within 7%.b) Particle transmission through the CCN low pressure inlet was assessed using two TSI 3772 CPCs: one placed before the inlet at approximately 995 hPa, and one after the inlet at reduced pressure of 650 hPa.The mean ratio of the reduced pressure CPC to the ambient pressure CPC for nearly monodisperse AS particles at several diameters ranging between 35 nm and 110 nm was 0.67, which compares well with the expected reduction by a factor of approximately 0.65.However, the ratio of the CPCs varied between 0.6 and 0.76 with the higher values at smaller particle sizes (Figure S1).The reason for the variation is unknown, but it suggests that the CCNC concentrations sampled through this low-pressure inlet may be artificially increased for particles <70 nm and reduced for particles >70 nm by up to 8%.

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