Abstract
To date, the relative contribution of primary marine organic matter to the subset of atmospheric particles that nucleate cloud droplets is highly uncertain. Here, cloud condensation nuclei (CCN) measurements were conducted on aerosolized sea surface microlayer (SML) samples collected from the North Atlantic Ocean during the NASA North Atlantic Aerosols and Marine Ecosystems Study (NAAMES), κ values were predicted for three representative high molecular weight (HMW) organic components of marine aerosol: 6-glucose, humic acid, and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The predicted κ values for pure organic aerosols varied by only ±0.01 across all of the organics chosen. For the desalted SML samples, calculations assuming an organic composition of entirely RuBisCO provided the closest predicted κ values for the desalted SML samples with a mean κ value of 0.53 ± 0.10. These results indicate that it is the sea salt in the SML which drives the cloud formation potential of marine aerosols. While the presence of organic material from the ocean surface waters may increase aerosol mass due to enrichment processes, cloud formation potential of mixed organic/salt primary marine aerosols will be slightly weakened or unchanged compared to sea spray aerosol.
Highlights
Marine aerosol-cloud interactions represent one of the largest uncertainties in understanding climate change (Carslaw et al, 2013; IPCC, 2014; Brooks and Thornton, 2018)
The critical diameters and κ values derived from cloud condensation nuclei (CCN) measurements of aerosolized surface microlayer (SML) and desalted SML (DSML) samples are shown in Figures 4A,B, respectively
These data suggested that the desalting process affected κ values more than the variation in organic matter between stations
Summary
Marine aerosol-cloud interactions represent one of the largest uncertainties in understanding climate change (Carslaw et al, 2013; IPCC, 2014; Brooks and Thornton, 2018). Some aerosols act as cloud condensation nuclei (CCN) by providing sites onto which cloud droplets form. Natural events such as phytoplankton blooms may influence aerosol production and have a large impact on climate. Aerosols containing large surfactants may enter the atmosphere and act as CCN to form clouds (Quinn et al, 2015; Brooks and Thornton, 2018). CCN production can occur through secondary aerosol formation resulting from
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