Airborne Organic Aerosol Characterization in the Los Angeles Basin, California, During the AEROMMA 2023 Summer Campaign

SARAH ALBERTIN, Alison Piasecki, Ann M. Middlebrook, Science Team AEROMMA, CU-CIRES/NOAA CSL

     Abstract Number: 605
     Working Group: Carbonaceous Aerosols

Abstract
The NOAA Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) experiment operated a large suite of instruments onboard the NASA DC-8 aircraft during the summer of 2023 to address critical scientific questions around emergent emissions and chemical transformations in U.S. urban areas. In particular, the emergence of poorly characterized and regulated volatile organic compounds, along with biogenic emissions pose a continuous challenge to our understanding of the processes driving organic aerosol (OA) formation and future air quality.

In this study, we report OA measurements over the Los Angeles (LA) basin for 3 afternoon research flights using a high-resolution time-of-flight aerosol mass spectrometer. Overall, the aerosol mass is dominated by organic components (74 % on average), with a pronounced mass concentration gradient from the eastern LA urban area, to the harbor area and to the open ocean. Variability in OA mass concentration is observed as a function of time of day. In particular, the OA mass concentration in the LA urban area peaks at mid-afternoon, as observed in previous studies. Primary OA (POA) and oxygenated OA (OOA) components are identified using positive matrix factorization. Different OOA factors are resolved, showing a spatial evolution of OOA in the area. Notably, a fresher OOA is found to be the largest OA contributor over the LA basin. POA also exhibits an important east-west gradient and correlates with primary anthropogenic tracers. Future work will further characterize these components, using complementary aerosol and gas phase measurements taken on board the DC-8 during AEROMMA. Comparisons with previous studies in the LA basin will be presented, showing the evolution of OA composition and sources over the past decade in this area.