Seasonal Variations in Western North Atlantic Remote Marine Aerosol Properties

Abstract

The impact of ocean ecosystems on marine boundary layer aerosols and clouds has been the subject of much research but remains uncertain. Five experiments were recently conducted in the western North Atlantic to assess if the seasonally recurring phytoplankton bloom affects aerosol properties. These experiments include the second Western Atlantic Climate Study and four North Atlantic Aerosols and Marine Ecosystem Study cruises. Measurements of unheated and heated number size distributions, cloud condensation nucleus (CCN) concentrations, and aerosol composition were used to identify primary and secondary aerosol components that could be related to the state of the bloom. Only periods of clean marine air, as defined by radon, particle number concentrations, aerosol light absorption coefficient, and back trajectories, were included in the analysis. Nonvolatile material was found to be prevalent in the Aitken mode size range after heating to 230°, likely due to downward mixing from the free troposphere. CCN concentrations at 0.1% supersaturation were best correlated (r2 = 0.73) with accumulation mode nss SO4=. Sea spray aerosol was only correlated with CCN during November when bloom accumulation had not yet occurred and dimethylsulfide concentrations were at a minimum. The fraction of CCN attributable to sea spray aerosol was less than 20% during March, May/June, and September, indicating the limited contribution of sea spray aerosol to the CCN population of the western North Atlantic atmosphere. The strongest link between the plankton bloom and aerosol and cloud properties appears to be due to biogenic non‐sea salt SO4=.

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

“…NR‐SO 4 = accounted for between 22% and 27% of submicron mass during ambient marine periods (except for winter which had only 9%). Absolute and relative NR‐SO 4 = concentrations during ambient marine periods varied significantly by season and were highest during late spring (0.44 ± 0.24 μg/m 3 ) and lowest during winter (0.15 ± 0.14 μg/m 3 ), consistent with higher atmospheric DMS concentrations measured during late spring (311 ± 300 pptv) compared to the other campaigns (67 ± 7 pptv in winter, 100 ± 66 pptv in autumn, and 140 ± 36 pptv in early spring), as found previously (Quinn et al, 2019). The seasonal range of NR‐SO 4 = concentrations reported in this study is comparable to previous measurements in the North Atlantic (Huebert, Zhuang, et al, 1996; Seguin et al, 2011) and the South Pacific (Bates et al, 1992; Jung et al, 2014).…”

“…Several coastal studies reported strong correlations between chlorophyll and the organic fraction of the sea-spray particles for marine periods (Cavalli et al, 2004;O'Dowd et al, 2004O'Dowd et al, , 2015Ovadnevaite et al, 2014). Shipboard measurements in open ocean conditions from multiple oceans do not support a hypothesized link between primary ocean production and organic enrichment of the aerosol (Beaupré et al, 2019;Kasparian et al, 2017;Keene et al, 2017;Kieber et al, 2016;Quinn et al, 2014Quinn et al, , 2019. For example, Quinn et al (2014) and Bates et al (2020) used sea sweep (a floating bubbler that generates and samples sea-spray particles) and reported no statistically significant differences in the organicto-sodium content of the generated submicron aerosol particles in oligotrophic and eutrophic waters in the Western Atlantic and Eastern Pacific oceans.…”

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

“…All samples were analyzed by transmission FTIR using an automated fitting algorithm and techniques described previ-ously (Maria et al, 2002;Russell et al, 2009;Takahama et al, 2013).…”

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

“…These techniques have the potential to detect both refractory and labile components of the organic matter in marine aerosols, and therefore contribute to our understanding of the composition and origin of this material. The samples analyzed here were collected during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) (Behrenfeld et al, 2019). One of the main study goals was the characterization of the seasonal influence of surface ocean ecosystems on atmospheric aerosols.…”