Collaborative Research: Coastal Cloud Chemistry during the Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE-CCC)

This project is focused on the study of cloud chemistry in support of improvements in how cloud formation is represented in climate models. A suite of advanced chemical measurements will be made at the Scripps Pier and at nearby Mt. Soledad to augment the Department of Energy’s Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) campaign to be conducted in La Jolla California from February 2023 to January 2024. This effort will provide an unprecedented characterization of cloud chemical processing that is expected to help reduce a major uncertainty in climate model predictions. This project adds advanced chemical characterization of clouds to EPCAPE by leveraging recent instrument developments of single-particle mass spectrometry techniques, miniaturized static thermal gradient cloud condensation nuclei (CCN) instruments, and a custom-designed instrument for measuring aqueous hydroxyl (OH) radicals formed in nascent cloud droplets (the OH "burst"). The sampling strategy enables testing of the following hypotheses: (1) The subset of the aerosol population that is activated to cloud droplets is chemically distinct from the unactivated particles, and its size-resolved chemical composition is further differentiated by adding aqueous-oxidized components that can be identified in single-particle mass fragments. The chemical changes lower the activation supersaturation required for subsequent activation of particles, which in turn may affect cloud structure and drop distributions. (2) Gas-phase compounds that are removed by denuding will lower the supersaturation required for activation of each particle by enhancing water solubility during the uptake process. The effect is expected to depend on the amount of pollution influence, on the composition and concentration of gaseous species, and on particle size. (3) Particles with longer times between cloud cycles will produce a larger OH burst, and as a result, larger changes to particle chemical composition during cloud cycling. The OH burst activity, together with the availability of gas phase species will explain much of the variation in the chemical changes observed between cloud events. This effort includes the training of graduate and undergraduate students in instrument maintenance and measurement analyses to prepare the next generation of scientists for conducting atmospheric research. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.