The Plankton, Aerosol, Cloud, ocean Ecosystem Postlaunch Airborne eXperiment (PACE-PAX) is a September, 2024, field campaign to gather data for the validation of the recently launched PACE mission. The operational area is Southern and Central California and nearby coastal regions. 84 flight hours are planned for NASA ER-2 operating out of the NASA Armstrong Flight Research Center and 60 for the CIRPAS Twin Otter flying out of Marina Municipal Airport. A NOAA vessel, the R/V Shearwater, will operate out of Santa Barbara.