Ozone oxidation of oleic acid surface films decreases aerosol cloud condensation nuclei activity

Abstract

[1] Heterogeneous oxidation of aerosols composed of pure oleic acid (C 18 H 34 O 2 , an unsaturated fatty acid commonly found in continental and marine aerosol) by gas-phase O 3 is known to increase aerosol hygroscopicity and activity as cloud condensation nuclei (CCN). Whether this trend is preserved when the oleic acid is internally mixed with other electrolytes is unknown and addressed in this study. We quantify the CCN activity of sodium salt aerosols (NaCl and Na 2 SO 4 ) internally mixed with sodium oleate (SO) and oleic acid (OA). We find that particles containing roughly one monolayer of SO/OA show similar CCN activity to pure salt particles, whereas a tenfold increase in organic concentration slightly depresses CCN activity. O 3 oxidation of these multicomponent aerosols has little effect on the critical diameter for CCN activation for unacidified particles at all conditions studied, and the activation kinetics of the CCN are similar in each case to those of pure salts. SO-containing particles which are acidified to atmospherically relevant pH before analysis in order to form oleic acid, however, show depressed CCN activity upon oxidation. This effect is more pronounced at higher organic concentrations. The behavior after oxidation is consistent with the disappearance of the organic surface film, supported by Köhler Theory Analysis (KTA). The -Köhler calculations show a small decrease in hygroscopicity after oxidation. The important implication of this finding is that oxidative aging may not always enhance the hygroscopicity of internally mixed inorganic-organic aerosols.

Inorganic salts interact with oxalic acid in submicron particles to form material with low hygroscopicity and volatility

“…Loss of volatile products occurs at the particle surface, leading to enrichment of the remaining lower volatility material at the particle surface. When present at the particle surface, only small amounts of low-solubility material are required to strongly affect particle hygroscopicity (Schwier et al, 2011). A recent study has directly shown surface enrichment of di-valent material in naturally occurring sea-salt aerosol (Ault et al, 2013).…”

Impact of marine biogeochemistry on the chemical mixing state and cloud forming ability of nascent sea spray aerosol

“…Table 1 provides a review of a number of reports of CCN activity measurements from both laboratory and field studies (including this work). The assessment of modern anthropogenic aerosol impacts on cloud properties King et al [2012] 1.25, 1.08 NaCl and artificial seawater, respectively Fuentes et al [2011] v1.3-1.5 "Seawater proxy" no organics; κ depends on a w Niedermeier et al [2008] 1 Other Relevant Model and Natural Systems King et al [2012]~1.25 a 60 g NaCl + 1 g sodium laurate, aqueous 0.2 a 0.27 g NaCl + 1 g sodium laurate, aqueous Frosch et al [2011] 0.57 50% oxalic acid, 50% NaCl 0.38 80% oxalic acid, 20% NaCl Moore et al [2011] 1.1 a >Bilayer oleic acid on NaCl (aq) 1.3 a >Bilayer sodium dodecyl sulfate on NaCl (aq) Schwier et al [2011] 1 depends critically on the concentrations of natural aerosol [Menon et al, 2002;Lohmann and Feichter, 2005], although this information has been difficult to assess [Andreae, 2007], stressing the importance of detailed characterization of the sources and properties of natural aerosol particles.…”

“…Seasonal phytoplankton blooms that lead to regionally elevated dissolved and particulate organic matter (OM sea ) concentrations in the ocean [Ducklow et al, 1995] have been associated with reports of strong enhancements in the organic mass fraction of submicron aerosol [O'Dowd et al, 2004;Yoon et al, 2007] at Mace Head, Ireland. Subsequent investigations into the influence of organic material on the CCN activity of sea salt/organic mixtures have mostly utilized model chemical systems (e.g., oleic acid, amino acids, surfactants) to simulate varying concentrations of OM sea that is ejected from the ocean, showing modest reductions in CCN activity with the addition of organics in many cases [Frosch et al, 2011;Moore et al, 2011;Schwier et al, 2011;King et al, 2012]. This weak influence of organics is likely related to the dominant effect of the highly water soluble inorganic components on the CCN activation of internally mixed salt/organic particles [Bilde and Svenningsson, 2004;Broekhuizen et al, 2004], the lack of long-range molecular order in the organic films [Davies et al, 2013], and the relatively low viscosity of the organic proxies [Shiraiwa et al, 2011;Bones et al, 2012].…”

Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water

“…aerosols such as toxicity, reactivity, ice and cloud condensation nucleation abilities, and radiative properties (FinlaysonPitts and Pitts, 1997;George and Abbatt, 2010b;Kolb et al, 2010;Kuwata et al, 2011;Lu et al, 2011;Schwier et al, 2011;Wang and Knopf, 2011;Shiraiwa et al, 2012). Gasparticle partitioning of semi-volatile species is a key process for formation and aging of secondary organic aerosol (Odum et al, 1996;Seinfeld and Pankow, 2003;Donahue et al, 2006;Robinson et al, 2007;Hallquist et al, 2009;Jimenez et al, 2009;Riipinen et al, 2011).…”