Influence of Urban and Marine Aerosol on Coastal Cloud Processing at Mt. Soledad in Southern California during EPCAPE
RYAN FARLEY, Kyle Gorkowski, James E. Lee, Katherine Benedict, Abu Sayeed Md Shawon, Nevil Franco, Veronica Berta, Lynn M. Russell, Manvendra Dubey, Allison Aiken, Los Alamos National Laboratory
Abstract Number: 351
Working Group: Coast to Coast Campaigns on Aerosols, Clouds, Chemistry, and Air Quality
Abstract
Anthropogenic aerosol influence marine cloud properties in many coastal regions, but their impacts and interactions remain poorly understood due to their complexity and difficulty in observing these processes in situ. Cloud interactions are a significant but highly uncertain removal process for aerosol with the removal rates depending on aerosol composition. Additionally, the chemical transformations of material within cloud droplets can significantly alter the composition, cloud and ice activation, and optical properties of the aerosol following droplet evaporation. In this work, measurements of aerosol chemical, physical, optical, and hygroscopic properties were collected at the Mt. Soledad site in La Jolla, CA (elevation 250m, 2 km from shore) as part of the Eastern Pacific Cloud Aerosol Precipitation Experiment Partitioning Thrust by Los Alamos National Laboratory (EPCAPE-PT-LANL) from October to December 2023. A ground based counterflow virtual impactor was utilized to directly measure the properties of cloud droplet residuals and compare with aerosols measured immediately adjacent to cloud periods. Two in-cloud periods are presented with different airmass trajectories, one from the north and one from the south. A comparison of the high-resolution aerosol mass spectrometer measurements of droplet residuals and out of cloud particles highlight the role of cloud processing on altering aerosol composition. Specifically, inorganic nitrate fraction increased 2-fold and chloride fraction increased 3-fold relative to the interstitial (non-activated) aerosol. Differences in VOC concentrations measured by Proton Transfer Mass spectrometry (PTR-MS) during the cloud events and their role in SOA formation will also be discussed. Source apportionment analysis revealed that this site is impacted by both marine sources and transported pollutants from local and regional urban centers, providing an ideal opportunity to characterize cloud processing from the East Pacific under varying conditions at the coast. These results help constrain the role of different aerosol sources on cloud formation and properties.