Marine and Anthropogenic Effects on Ultrafine Aerosol Composition during the Eastern Pacific Cloud Aerosol Precipitation Experiment
ANNA KAPP, Kristen Cramer, Nhu-Naomi Nguyen, James Smith, Univeristy of California, Irvine
Abstract Number: 243
Working Group: Coast to Coast Campaigns on Aerosols, Clouds, Chemistry, and Air Quality
Abstract
Oceans produce primary sea spray aerosol in addition to contributing to the production of gases that oxidize to form secondary marine aerosol. Coastal cities are influenced by both marine and anthropogenic aerosol precursors. The extent to which marine influence is present in aerosol composition in coastal cities and how marine aerosol precursors interact with anthropogenic compounds are poorly understood. To address this, the Eastern Pacific Cloud Aerosol Precipitation Experiment-Ultrafine Particle Properties (EPCAPE-UPP) campaign took place from April 15th to June 15th, 2023, in La Jolla, California. La Jolla is subject to heavily polluted winds from Los Angeles, but it is also influenced by “clean marine” background winds from the Pacific Ocean, making it the perfect place to examine particles formation from marine and urban emissions.
We report measurements from a hygroscopicity tandem differential mobility analyzer (HTDMA). Measured growth factors at 85% RH ranged from 1.1 and 1.3, suggesting that particles at the site are mostly made up of a mixture of organic compounds and sulfate. Volatility tandem differential mobility analyzer (VTDMA) measurements found that most ultrafine particles volatilized between 80°C and 160°C which rules out a major contribution from NaCl to ultrafine particle composition and is consistent with HTDMA-derived growth factors. We also measured size-resolved particle composition using thermal desorption chemical ionization mass spectrometry (TDCIMS). Those measurements show that ultrafine particles contained some NaCl at the beginning of the campaign, indicating that the first few weeks of were a period of particular influence by marine processes in La Jolla. Other compounds, including amines and multifunctional organics, were detected in particles and point to specific processes responsible for ultrafine particle growth.