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Abstract

Aerosol particles play a critical role as cloud condensation nuclei (CCN) in the atmosphere. The CCN ability is conventionally measured using CCN counters (CCNCs), which determine the proportion of particles that activate into cloud droplets when exposed to water vapor at a pre-set supersaturation. However, recent findings suggest that the co-condensation effect of semi-volatiles can greatly enhance aerosol particle growth, for example, in polluted cities. This co-condensation effect is not captured accurately in conventional CCNCs, such as streamwise CCNC developed by DMT Inc, since the particles are heated as they pass through the CCNC column. To address this limitation, we have developed the Horizontal Cloud Condensation Nuclei Counter (H-CCNC) based on the concept of a continuous-flow thermal-gradient diffusion chamber. The H-CCNC operates at lower temperatures (<10°C) than the commercial streamwise CCNC, allowing for the evaluation of the co-condensation effect of semi-volatile species that would otherwise partition to the gas phase. In this study, we present the results of our 3D geometry and computational fluid dynamics simulations of the H-CCNC using the ANSYS software with real laboratory boundary conditions and discuss the improvements to maintain uniform temperature distributions along the walls through refrigeration. We present the designs and validation of the newly built H-CCNC using non-volatile particles with no surface activity (i.e., ammonium sulfate) to verify the performance of the instrument with κ-Köhler values found in the literature.