Ultrafine Aerosol Particle Formation and Impacts During EPCAPE

Abstract

This project will answer the questions: “What is the composition of ultrafine (sub-100 nm diameter) marine aerosol particles?” and “How does their composition relate to climatically important properties?” Our main activity will be measurements of the chemical and physical properties of ultrafine particles during the Eastern Pacific Cloud Aerosol and Precipitation Experiment (EPCAPE) near San Diego, CA, during 15 April to 15 June 2023. EPCAPE provides a unique opportunity to explore the properties of newly formed and aged marine particles and the relationships between particle composition and cloud formation. Our approach will combine direct measurements of size-selected ultrafine particles together with measurements of size-selected ultrafine particle hygroscopicity and vola­tility. While the focus of this project is on the formation and evolution of ultrafine particles in a marine setting, the measurements and insights gained will be directly applicable to the formation and evolution of larger particles, with implications for air quality and climate in this important urban region.

Based on our prior measurements, we hypothesize that ultrafine marine particles are composed of varying amounts of sea salt and primary organic compounds and these particles likely further evolve in the atmosphere from the uptake of secondary inorganic and organic compounds depending on the presence of condensable vapors from the sea surface and from anthropogenic sources. Our project will have three main objectives that will directly address our hypotheses. Our first objective is the previously mentioned measurements of ultrafine particle composition, hygroscopicity, and volatility at the Mt. Soledad field site during the EPCAPE intensive observation period. Our second objective is to analyze our data, leveraging other relevant observations, in order to understand the dominant species and processes responsible for ultrafine particle formation in this setting. Several data products will be generated and archived on the DOE ARM server that will benefit the entire scientific community. Finally, our third objective is to connect our measurements of size-resolved ultrafine aerosol properties with climatically important processes that are a major focus of EPCAPE.  This includes collaborating with modelers by providing data on processes that we discover from our EPCAPE observations in order to better represent the production and sinks that govern atmospheric aerosol formation, evolution, and climate impacts.