Aerosol source and composition strongly affect the ability of particles to act as cloud condensation nuclei (CCN), influencing precipitation and radiative forcing. This study employs aircraft data from the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE) campaign over the Southern Great Plains to quantify activated fraction and CCN closure under varying environmental conditions. Hybrid Positive Matrix Factorization was implemented for source apportionment across spring and fall for air masses originating from four U.S. regions. An external mixture best represented the aerosol, and organic hygroscopicity depended strongly on air mass origin and altitude, increasing above 2000 m. Multivariable linear regression showed that organic hygroscopicity correlates not only with chemical composition but also with air mass origin, temperature, and relative humidity, underscoring the need to consider both air mass and chemistry when modeling aerosol-cloud interactions.