Data for: Low temperature ice nucleation of sea spray and secondary marine aerosols under cirrus cloud conditions

Sea spray aerosols (SSA) represent one of the most abundant aerosol types
on a global scale and have been observed at all altitudes including the
upper troposphere. SSA has been explored in recent years as a source of
ice nucleating particles (INPs) in cirrus clouds due to the ubiquity of
cirrus clouds and the uncertainties in their radiative forcing. This study
expands upon previous works on low temperature ice nucleation of SSA by
investigating the effects of atmospheric aging of SSA and the ice
nucleating activity of newly formed secondary marine aerosols (SMA) using
an oxidation flow reactor. Polydisperse aerosol distributions were
generated from a Marine Aerosol Reference Tank (MART) filled with 120 L of
real or artificial seawater and were dried to very low relative humidity
to crystallize the salt constituents of SSA prior to their subsequent
freezing, which was measured using a Continuous Flow Diffusion Chamber
(CFDC). Results show that for both primary SSA (pSSA), and the aged SSA
and SMA (aSSA+SMA) at temperatures > 220 K, homogeneous conditions
(92–97 % relative humidity with respect to water (RHw)) were required to
freeze 1 % of the particles. However, below 220 K, heterogeneous
nucleation occurs for both pSSA and aSSA+SMA at much lower RHw, where up
to 1 % of the aerosol population freezes between 75–80 % RHw. Similarities
between freezing behaviors of the pSSA and aSSA+SMA at all temperatures
suggest that the contributions of condensed organics onto the pSSA or
alteration of functional groups in pSSA via atmospheric aging did not
hinder the major heterogeneous ice nucleation process at these cirrus
temperatures that has previously been shown to be dominated by the
crystalline salts. Occurrence of 1% frozen fraction of SMA, generated in
the absence of primary SSA, was observed at/near water saturation below
220 K, suggesting it is not an effective INP at cirrus temperatures,
similar to findings in the literature of other organic aerosols. Thus, any
SMA coatings on the pSSA would only decrease the ice nucleation behavior
of pSSA if the organic components were able to significantly delay water
uptake of the inorganic salts, and apparently, this was not the case.
Results from this study demonstrate the ability of lofted primary sea
spray particles to remain an effective ice nucleator at cirrus
temperatures, even after atmospheric aging has occurred over a period of
days in the marine boundary layer prior to lofting. We were not able to
address aging processes under upper tropospheric conditions.