Aerosol size distributions and cloud condensation nuclei spectra and their temporal variability in the Southern Great Plains
Authors
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Ezra Ezra Levin Levin — Colorado State University
Don R. Collins — University of California, Riverside
Sonia Kreidenweis — Colorado State University
Category
General topics – Aerosols
Description
An aerosol size distribution dataset spanning a large diameter range (Dp = 7 nm – 14 µm) was developed using measurements from a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), and a condensation particle counter (CPC) at the Southern Great Plains (SGP) site for the years 2009 - 2013. These data were used to calculate seasonally representative aerosol number, surface area and volume distributions for SGP and to investigate seasonal changes in aerosol concentrations in different size bins. While the seasonal median size distributions had similar shapes (4 lognormal modes), there were significant differences between seasons, especially for the smallest (Dp < 30 nm) and largest (Dp > 800 nm) particles, indicating the different processes important in controlling the aerosol size distributions during different seasons. We also employed power spectral analysis to determine the main temporal cycles for total and size binned aerosol concentrations. The dominant cycle for total number concentrations was a 24-hour, diurnal cycle. This diurnal cycle was driven by changes in the number concentrations of particles with Dp < 30 nm, likely due to new particle formation events. This cycle was observed in all seasons, in ~50% of the observations, with peak number concentrations occurring in the local afternoon and evening hours, but differing by several hours depending on the season. Finally, these size distributions were used to calculate cloud condensation nuclei (CCN) spectra using size resolved aerosol hygroscopicity measurements from a humidified tandem differential mobility analyzer (HTDMA). The wide diameter range in the merged size distribution dataset allows for extension of the CCN spectra to much lower and higher supersaturations than can be measured directly with a CCN counter. We also used the seasonal size distributions to calculate characteristic CCN spectra for each season at SGP.
