AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Changes in CCN Solubility from Cloud Processing
STEPHEN NOBLE, James Hudson, Desert Researh Institute
Abstract Number: 400 Working Group: Aerosol Chemistry
Abstract Cloud processing (physical: collision-coalescence and Brownian capture; chemical: aqueous oxidation) changes activated cloud condensation nuclei (CCN). When droplets evaporate they leave modified CCN. Activated CCN collect material from cloud processing, which affect size, solubility (kappa, here K), and critical supersaturation (S$_c). Thus, these processed CCN are larger (lower S$_c) and separate from unactivated CCN creating bimodal spectra with processed and unprocessed peaks. Comparison of CCN S$_c spectra with aerosol size spectra provides information about K. MArine Stratus/Stratocumulus Experiment (MASE) provided simultaneous CCN and DMA (differential mobility analyzer) aircraft measurements. MASE also provided bulk chemistry measurements. K was calculated from comparisons of CCN and DMA processed and unprocessed peaks (K$_p, K$_u). K$_u ranged from 0.06 to 1.28 and K$_p from 0.10 to 1.28. Mean K$_p (0.51) was larger than K$_u (0.45), while K from unimodal spectra was smallest (0.34). Bimodal spectra were also associated with higher Na$^+, Cl$^-, SO$_4$^(2-), and NO$_3$^- measurements as well as lower SO$_2 and O$_3 measurements. This suggests that aqueous oxidation of dissolved gases increased K$_p during cloud processing. However, for some spectra K$_u was larger than K$_p. The majority of these coincided with strong horizontal winds (>8.5 m/s). Larger wind speeds increase sea spray leading to finer sea salt particles. At these high winds K$_u, K$_p, Na$^+, Cl$^-, SO$_4$^(2-), and NO$_3$^- measurements were larger. Also, larger SO$_2 and O$_3 concentrations were concurrent with unimodal spectra, which likely preceded cloud processing. Thus, the larger K$_u near K for sea salt is reduced by chemical processing making lower K materials and smaller K$_p. For other cases of K$_u>K$_p, cloud droplets most likely collect the smallest CCN (high S$_c, low K) via Brownian capture reducing K$_p. CCN solubility can remain fixed, increase, or decrease from cloud processing depending on the previous material and processing type.