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In-situ Physical and Chemical Characterization of Cloud Droplet Residuals, Interstitial, and Background Aerosol Particles During the HI-SCALE Field Campaign
GEORGES SALIBA, Alla Zelenyuk, David Bell, Kaitlyn J. Suski, John Shilling, Fan Mei, Gourihar Kulkarni, Jian Wang, Jason Tomlinson, Jerome Fast, Pacific Northwest National Laboratory
Abstract Number: 554
Working Group: Aerosols, Clouds and Climate
Abstract
Shallow cumulus clouds are an important part of the Earth’s radiative budget with radiative cooling forcing on the order of tens of W/m2. However, shallow cumulus clouds are an important source of uncertainty in most climate models because these clouds have length scale that are smaller than grids cell size and their representation in climate models often rely on parameterizations. Some geographic regions, like the southern Great Plains, are an ideal place to study land-atmosphere interactions that significantly affect the shallow cumulus clouds formation and lifetime because of strong gradients in soil type and moisture, biogenic and anthropogenic emissions, as well as frequent new particle formation events. Here, we present results from the Holistic Interactions of Shallow Clouds, Aerosols and Land Ecosystems (HI-SCALE) field campaign at the U.S. Department of Energy’s Atmospheric Radiation Measurements (ARM) Climate Research Facility’s Southern Great Plains (SGP) site in Oklahoma. Measurements were conducted during the spring and summer seasons of 2016, when strong surface heating induces intense turbulence and higher biogenic fluxes of organic vapor precursors. Airborne measurements onboard the ARM Aerial Facility’s Gulfstream 1 (G-1) included particle number size distributions of background, interstitial, and cloud droplet residuals aerosol particles between 0.01 and 10 µm dry diameter and chemical composition of submicron bulk (using an Aerosol Mass Spectrometer, AMS) and individual aerosol particles (using PNNL’s single particle mass spectrometer, miniSPLAT), cloud condensation nuclei (CCN) concentrations, and cloud droplet concentrations. We will present a detailed comparison between the size distributions, densities, and size-dependent mixing state of aerosol sampled below cloud, cloud droplet residuals, and interstitial particles to understand the effect of particle physicochemical properties on their CCN activity and examine the effect of cloud processing and aqueous chemistry on size and composition of cloud droplet residuals. In addition, we will explore the variability in droplet and particle number concentrations, aerosol size, and chemical composition, which can alter in-cloud maximum supersaturations, to understand the large observed variability in the fraction of activated cloud droplets during the HI-SCALE campaign.