Abstract
Abstract. The concentrations of cloud condensation nuclei (CCN) modulate cloud properties, rainfall location and intensity, and climate forcings. This work assesses uncertainties in CCN measurements and the apparent hygroscopicity parameter (κapp), which is widely used to represent CCN populations in climate models. CCN measurements require accurate operation of three instruments: the CCN instrument, the differential mobility analyzer (DMA), and the condensation particle counter (CPC). Assessment of DMA operation showed that varying the ratio of aerosol to sheath flow from 0.05 to 0.30 resulted in discrepancies between the κapp values calculated from CCN measurements and the literature value. Discrepancies were found to increase from <1 % to 13 % for both sodium chloride and ammonium sulfate. The ratio of excess to sheath flow was also varied, which shifted the downstream aerosol distribution towards smaller particle diameters (for excess flow < sheath flow) or larger particle diameters (for excess flow > sheath flow) than predicted. For the CPC instrument, undercounting occurred at high concentrations, resulting in calculated κapp lower than the literature values. Lastly, undercounting by CCN instruments at high concentration was also assessed, taking the effect of supersaturation on counting efficiency into account. Under recommended operating conditions, the combined DMA, CPC, and CCN uncertainties in κapp are 1.2 % or less for 25 to 200 nm diameter aerosols.
Highlights
Aerosol–cloud interactions represent a major uncertainty in current predictions of the Earth’s climate (IPCC, 2013)
cloud condensation nucleus (CCN) measurements used for calculating apparent hygroscopicity from monodisperse aerosol require accurate operation of three instruments: the CCN, the differential mobility analyzer (DMA), and the condensation particle counter (CPC)
The sensitivity of weather and climate models to accuracy in CCN activation predictions has been demonstrated in other works
Summary
Aerosol–cloud interactions represent a major uncertainty in current predictions of the Earth’s climate (IPCC, 2013). One parameterization was designed to represent the cloud droplet activation potential ambient aerosol masses of unknown composition with a single variable, kappa (κ), based on the dry aerosol’s hygroscopicity or ability to uptake water and form a solution droplet (Petters and Kreidenweis, 2007). Kreidenweis et al (2005) determined that the critical activation diameter of dry aerosol particles can be calculated from simplified Köhler theory using the physical properties of water and the solute in a solution droplet. This parameterization has been used in CCN closure studies (Bougiatioti et al, 2009; Moore et al, 2011, 2012a). By systematically quantifying sources of experimental error, this study provides a framework for determining the significance of variations in CCN properties reported in multiple studies and defining the operating conditions that minimize instrumental artifacts
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
