Aerosol Properties Observed during the CACTI Campaign in Argentina

JEROME FAST, Fan Mei, Jason Tomlinson, Mikhail Pekour, Beat Schmid, Alla Zelenyuk, Arthur J. Sedlacek, Maria Zawadowicz, Bin Zhao, Po-Lun Ma, Adam Varble, Pacific Northwest National Laboratory

     Abstract Number: 58
     Working Group: Aerosols, Clouds and Climate

Abstract
The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was conducted over the Sierras de Cordoba range in north-central Argentina between October 2018 and April 2019 to better understand the role of atmospheric thermodynamics, topographic forcing, and aerosols on the lifecycle of convective clouds. The extreme storms in this region are some of the deepest, largest, and longest-lived on Earth. The extensive CACTI measurements thus provide an opportunity to better understand interactions between aerosols and convective cloud properties that are highly uncertain. As a first step, this study characterizes the spatial and temporal variations in aerosol number, mass, size, composition, compositional mixing state, and cloud condensation nuclei using both ground and airborne instrumentation. Aerosol properties were found to be strongly controlled by changing synoptic meteorological conditions. The northerly low-level jet along the eastern side of the Andes frequently transports biomass burning aerosols from the southern Amazon basin into Argentina. When the winds shift to the south, concentrations of accumulation mode aerosols decrease as concentrations of coarse dust particles originating from Patagonia increase. Accumulation mode aerosols on some days are highly correlated with carbon monoxide, suggesting the aerosols primarily originate from anthropogenic or biomass burning sources. This correlation is weak on other days, suggesting natural sources dominate. Ground and aircraft measurements are combined and analyzed to determine whether increases in surface ultrafine particle concentrations are due to downward entrainment from the lower free troposphere or local new particle formation events in the boundary layer. Since relatively few in situ aerosol measurements have been collected in the southern hemisphere, CACTI measurements provide an opportunity to evaluate global model predictions. Therefore, we also compare E3SM model predictions, with and without new treatments of nucleation and ultrafine particles, to aircraft and ground measurements to help explain the possible mechanisms responsible for aerosol nucleation.