Seasonal Differences and Variability of Concentrations, Chemical Composition, and Cloud Condensation Nuclei of Marine Aerosol Over the North Atlantic

Abstract

The majority of the aerosol particle number (condensation nuclei or CN) in the marine boundary layer (MBL) consists of sulfate and organic compounds that have been shown to provide a large fraction of the cloud condensation nuclei (CCN). Here we use submicron non-refractory Aerosol Mass Spectrometer (AMS) and filter measurements of organic and sulfate components of aerosol particles measured during four North Atlantic Aerosol and Marine Ecosystems Study (NAAMES) research cruises to assess the sources and contributions of submicron organic and sulfate components for CCN concentrations in the MBL during four different seasons. Submicron hydroxyl group organic mass (OM) correlated strongly to sodium concentrations during clean marine periods (R ¼ 0.9), indicating that hydroxyl group OM can serve as a proxy for sea-spray OM in ambient measurements. Sea-spray OM contributed 45% of the sum of sea-spray OM and sea salt during late spring (biomass climax phase) compared to <20% for other seasons, but the seasonal difference was not statistically significant. The contribution of noncombustion sources during clean marine periods to submicron OM was 47 to 88% and to non-sea-salt sulfate 31 to 86%, with likely sources being marine and biogenic. The remaining submicron OM and sulfate were likely associated with ship or continental sources, including biomass burning, even during clean marine periods. The seasonal contribution from secondary sulfate and OM components to submicron aerosol mass was highest during late spring (60%), when biogenic emissions are expected to be highest, and lowest during winter (18%). Removing submicron sea-spray OM decreased CCN concentrations by <10% because of competing effects from increased hygroscopicity and decreased particle size. During all seasons, adding biogenic secondary sulfate increased hygroscopicity, particle size, and CCN concentrations at 0.1-0.3% supersaturations by 5-66%. The largest change was during early spring when the fraction of hygroscopic sulfate components in the 0.1-0.2 μm size range was highest (80%). During continental periods, the increased contribution from low-hygroscopicity organic components to 0.1-0.2 μm diameter particles reduces the CCN/CN by 20-100% for three seasons despite the increased CN and mass concentrations. These results illustrate the important role of the chemical composition of particles with diameters 0.1-0.2 μm for controlling CCN in the MBL.

North Atlantic marine organic aerosol characterized by novel offline thermal desorption mass spectrometry: polysaccharides, recalcitrant material, and secondary organics

“…Calcium : sodium was highly variable, and there was a large enrichment in calcium above seawater ratios, especially for the sub-180 nm aerosol (Table S2, Fig. S6), similar to what has been observed in previous sea spray generation experiments (Salter et al, 2016).…”

The impact of aerosol size-dependent hygroscopicity and mixing state on the cloud condensation nuclei potential over the Northeast Atlantic

“…for Clean-H, and were up to 37% for Clean-L at 0.75% SS. As shown in Table S3, the κHTDMA of Clean-L increased with particle size, and the trend was similar to previous ship-based observations in the North Atlantic where Aitken mode particles were more hygroscopic than accumulation mode particle because of the higher mass loading of nss-SO4 (Saliba et al, 2020). The relative differences in Clean-L sector increased with increasing SS, which confirmed the fact that Aitken mode particles were lesshygroscopic as would be the case with nss-SO4 vs sea-salt particles.…”

Measurement report: Cloud Processes and the Transport of Biological Emissions Regulate Southern Ocean Particle and Cloud Condensation Nuclei Concentrations

“…Data availability. SOCRATES CCN data can be found at https: //doi.org/10.5065/D6Z036XB (Sanchez and Roberts, 2018). The SOCRATES GV navigation and microphysics data can be found at https://doi.org/10.5065/D6M32TM9 (UCAR/NCAR, 2017).…”