Variability in Cloud Condensation Nuclei Spectra from Multiyear Measurements

For a distribution of aerosol particles, the number of aerosol particles that activate into cloud droplets can be represented as a function of supersaturation, often termed a cloud condensation nuclei (CCN) spectrum, and can be calculated via Köhler theory. CCN spectra incorporate both the aerosol particle size distribution and the aerosol hygroscopicity and provide information for understanding the microphysical impacts of aerosol particles on cloud systems. In this study, aerosol particle size distribution and size-resolved hygroscopicity observations from a hygroscopicity tandem differential mobility analyzer are used to calculate CCN spectra for multiple years at the Department of Energy’s Atmospheric Radiation Measurement Program Southern Great Plains site. Principal component analysis of this data demonstrates several important modes of variability in the CCN spectra, with the most dominant mode associated with relatively low and high concentrations of aerosol particles throughout the particle size distribution. Furthermore, the temporal scales of this variability are quantified, which can be used to provide guidance for representing evolving aerosol particle distributions when assessing aerosol effects on cloud systems.