Laboratory measurements of immersion freezing abilities of
non-proteinaceous and proteinaceous biological particulate proxies
Abstract
Non-proteinaceous and proteinaceous biological aerosols are abundant
within the atmosphere and have the potential to impact the climate
through cloud and precipitation formation. In this study, we present the
differences in the laboratory-measured freezing capabilities of the
non-proteinaceous and proteinaceous biological materials to determine
which has more potential to impact the ice nucleation in the clouds. As
non-proteinaceous surrogates, we examined multiple cellulose materials
(e.g., microcrystalline and nanocrystalline cellulose) whose sizes range
from ~100 nm to >100 μm (according to
manufacturer report). For proteinaceous proxies, we looked at different
gram-negative bacteria, such as Pseudamonas aeruginosa, Escherichia
coli, Serratia marcescens, Citrobacter freundii, and Snomax, (which
contains P. syringae) that can be found around the proximity of the
Texas Panhandle. By using the Cryogenic Refrigeration Applied Freezing
Test (CRAFT) system, we estimated immersion freezing efficiency (i.e.,
ice nucleation activity scaled to a unit of mass) of each sample at the
temperatures greater than -30°C. We have observed that not all
gram-negative bacteria has high immersion freezing activity, but the few
do have a warmer temperature onset (>-20 °C) than the
cellulose used. For those that did not exhibit substantial freezing
efficiencies, they had similar freezing properties as the broth, in
which the bacteria were incubated, as well as the cellulose materials
examined. These observations suggest the presence and potential
importance of bacterial cellulose in the atmospheric ice nucleation.
From here, we need to conduct more in-depth investigation in the effects
of a wider variety of atmospherically relevant biological aerosols to
get a better understanding of the effects of said aerosols on overall
aerosol-cloud interactions. Acknowledgments: K. Cory would like to
acknowledge NSF-EAPSI and JSPS Summer Program for the travel fellowship
support. N. Hiranuma acknowledges financial aids by the Higher Education
Assistance Fund (HEAF), WTAMU Office of Graduate School and Killgore
Research Center.