With oceans covering 71% of the Earth's surface, sea spray aerosol (SSA) particles play an important role in the global radiative budget by acting as cloud condensation nuclei and ice nucleating particles (INPs). By acting as INPs, SSA particles affect the structure and properties of mixed‐phase clouds by inducing freezing at warmer temperatures than the homogeneous freezing temperature. Climate models that incorporate marine INPs use the emission of submicron SSA in INP parameterizations because these particles contain a higher fraction of organic mass. Here we show supermicron SSA particles, produced using a natural breaking wave analogue, are the major source of INPs throughout the lifecycle of a phytoplankton bloom. Additionally, supermicron SSA particles are shown to be more efficient INPs than submicron SSA particles, because they carry a greater number of ice active components. Thus, supermicron SSA needs to be incorporated in INP parameterizations for future climate models.

Triacylglycerol lipases have recently been shown to be transferred from the ocean to the atmosphere in atmospheric sea spray aerosol (SSA). Lipases have the potential to alter the composition of SSA; however, the structure and properties of enzymes in the high salt, high ionic strength, and low pH conditions found in SSA have never been explored. Here, we study the dynamics of Burkholderia cepacia triacylglycerol lipase (BCL) at SSA model surfaces comprised of palmitic acid and dipalmitoylphosphatidic acid (DPPA), two commonly found lipids at SSA surfaces. Surface adsorption Langmuir isotherm experiments and all-atom explicit solvent molecular dynamics simulations together illuminate how and why BCL expands the ordering of lipids at palmitic acid surfaces the most at pH < 4 and the least in DPPA surfaces at pH 6. Taken together, these results represent a first glimpse into the complex interplay between lipid surface structure and protein dynamics within enzyme-containing aerosols.

Abstract. Ice-nucleating particles (INPs) are efficiently removed from clouds through precipitation, a convenience of nature for the study of these very rare particles that influence multiple climate-relevant cloud properties including ice crystal concentrations, size distributions and phase-partitioning processes. INPs suspended in precipitation can be used to estimate in-cloud INP concentrations and to infer their original composition. Offline droplet assays are commonly used to measure INP concentrations in precipitation samples. Heat and filtration treatments are also used to probe INP composition and size ranges. Many previous studies report storing samples prior to INP analyses, but little is known about the effects of storage on INP concentration or their sensitivity to treatments. Here, through a study of 15 precipitation samples collected at a coastal location in La Jolla, CA, USA, we found INP concentration changes up to > 1 order of magnitude caused by storage to concentrations of INPs with warm to moderate freezing temperatures (−7 to −19 ∘C). We compared four conditions: (1) storage at room temperature (+21–23 ∘C), (2) storage at +4 ∘C, (3) storage at −20 ∘C and (4) flash-freezing samples with liquid nitrogen prior to storage at −20 ∘C. Results demonstrate that storage can lead to both enhancements and losses of greater than 1 order of magnitude, with non-heat-labile INPs being generally less sensitive to storage regime, but significant losses of INPs smaller than 0.45 µm in all tested storage protocols. Correlations between total storage time (1–166 d) and changes in INP concentrations were weak across sampling protocols, with the exception of INPs with freezing temperatures ≥ −9 ∘C in samples stored at room temperature. We provide the following recommendations for preservation of precipitation samples from coastal or marine environments intended for INP analysis: that samples be stored at −20 ∘C to minimize storage artifacts, that changes due to storage are likely an additional uncertainty in INP concentrations, and that filtration treatments be applied only to fresh samples. At the freezing temperature −11 ∘C, average INP concentration losses of 51 %, 74 %, 16 % and 41 % were observed for untreated samples stored using the room temperature, +4, −20 ∘C, and flash-frozen protocols, respectively. Finally, the estimated uncertainties associated with the four storage protocols are provided for untreated, heat-treated and filtered samples for INPs between −9 and −17 ∘C.

Abstract. Ice nucleating particles (INP) have been found to influence the amount, phase, and efficiency of precipitation from winter storms, including atmospheric rivers. Warm INP, those that initiate freezing at temperatures warmer than -10 The sites are sufficiently close that airmass sources during this storm were almost identical, but the inland site was exposed to terrestrial sources of warm INP while the coastal site was not. Warm INP were more numerous in precipitation at the inland site by an order of magnitude. Using FLEXPART dispersion modelling and radar-derived cloud vertical structure, we detected 10 influence from terrestrial INP sources at the inland site, but did not find clear evidence of marine warm INP at either site. We episodically detected warm INP from long-range transported sources at both sites. By extending the FLEXPART modelling using a meteorological reanalysis, we demonstrate that long-range transported warm INP are observed only when the upper tropospheric jet provided transport to cloud tops. Using radar-derived hydrometeor classifications, we demonstrate that hydrometeors over the terrestrially-influenced inland site were more likely to be in the ice phase for cloud temperatures between