Cloud Condensation Nuclei Measurement Uncertainties: Implications for Cloud Models

摘要

Cloud condensation nuclei (CCN) spectra can be either measured directly or predicted using Kohler theory initialized with aerosol physicochemical property (APP) data. APP (aerosol composition and size spectra), the CCN spectrum, cloud droplet number concentration (CDNC), and vertical velocity (w) at the base of a convective cloud updraft are linked by what is commonly called the cloud droplet activation process. Using data sets obtained in cloud regions unaffected by entrainment and drizzle scavenging a comparison of predicted and observed droplet activation is possible. Assessments of the measurement uncertainties associated with APP, CCN, CDNC, and w are necessary for these closure studies. Here we summarize laboratory comparisons of CCN counter response to aerosols of known size and composition. Uncertainties associated with the CCN measurement are quantified. We also present field measurements from ACE-2. The latter show agreement between measured CDNC and predictions based on CCN and w. Also using ACE-2 data, we document a systematic bias between CDNC derived from APP, and CDNC derived from CCN. The implied disparity between CCN and APP is most pronounced when north-eastern Atlantic airmasses are influenced by continental pollution.