Organic composition of three different size ranges of aerosol particles over the Southern Ocean

• Main Authors: G. Saliba, K. J. Sanchez, L. M. Russell, C. H. Twohy, G. C. Roberts, S. Lewis, J. Dedrick, C. S. McCluskey, K. Moore, P. J. DeMott, D. W. Toohey
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Taylor & Francis 2020
• Subjects: Space Science; 29999 Physical Sciences not elsewhere classified; FOS Physical sciences; Molecular Biology; Biotechnology; Evolutionary Biology; FOS Biological sciences; 59999 Environmental Sciences not elsewhere classified; FOS Earth and related environmental sciences; 39999 Chemical Sciences not elsewhere classified; FOS Chemical sciences; Ecology; Inorganic Chemistry; Southern Ocean
• Online Access: https://dx.doi.org/10.6084/m9.figshare.13201085.v2; https://tandf.figshare.com/articles/online_resource/Organic_Composition_of_Three_Different_Size_Ranges_of_Aerosol_Particles_over_the_Southern_Ocean/13201085/2

Very few measurements exist of the composition and contribution to cloud condensation nuclei (CCN) of organic mass (OM) at different sizes for particles over the Southern Ocean. Airborne and shipboard measurements of organic composition, aerosol number and mass size distributions, and CCN spectra during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) provide a comparison of organic contributions at three different size ranges: (1) by scanning transmission X-ray microscope (STXM) with near edge X-ray absorption fine structure (NEXAFS) for particles 0.25–1.75 µm diameter, (2) by scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS) for particles 0.1–0.5 and 0.5–1µm diameter, and (3) indirectly by comparing CCN spectra to particle size distributions for particles <0.15 µm diameter. Organic functional groups from STXM-NEXAFS microscopy indicate that the majority of particles between 0.25 and 1.75 µm diameter with detectable organic components were consistent with marine organic signatures associated with sea spray particles, which was also true for ice nucleating particles sampled by immersion freezing 0.1 µm diameter were consistent with sodium-based sea spray and sulfate particles, providing closure between STEM and CCN measurements. Particles <0.15 µm diameter had kappa values of 0.2–0.5, indicating the substantial presence of OM at these sizes. The organic component fraction estimated from comparing the size distribution and supersaturation spectra varied from <10% to 70% for particles <0.15 µm diameter. This result shows the impact of the organic composition of particles <0.15 µm diameter on CCN concentrations at typical supersaturations for the SO. This variable OM fraction accounted for <0.1 µg/m 3 mass concentrations of particles smaller than 0.15 µm diameter but may play a role at cloud supersaturations greater than 0.3%. Copyright © 2020 American Association for Aerosol Research