The organic fraction of bubble-generated, accumulation mode Sea Spray Aerosol (SSA)

Abstract

Abstract. Recent studies have detected a dominant accumulation mode (∼100 nm) in the Sea Spray Aerosol (SSA) number distribution. There is evidence to suggest that particles in this mode are composed primarily of organics. To investigate this hypothesis we conducted experiments on NaCl, artificial SSA and natural SSA particles with a Volatility-Hygroscopicity-Tandem-DifferentialMobility-Analyser (VH-TDMA). NaCl particles were atomiser generated and a bubble generator was constructed to produce artificial and natural SSA particles. Natural seawater samples for use in the bubble generator were collected from biologically active, terrestrially-affected coastal water in Moreton Bay, Australia. Differences in the VH-TDMAmeasured volatility curves of artificial and natural SSA particles were used to investigate and quantify the organic fraction of natural SSA particles. Hygroscopic Growth Factor (HGF) data, also obtained by the VH-TDMA, were used to confirm the conclusions drawn from the volatility data. Both datasets indicated that the organic fraction of our natural SSA particles evaporated in the VH-TDMA over the temperature range 170-200 • C. The organic volume fraction for 71-77 nm natural SSA particles was 8±6%. Organic volume fraction did not vary significantly with varying water residence time (40 s to 24 h) in the bubble generator or SSA particle diameter in the range 38-173 nm. At room temperature we measured shape-and Kelvin-corrected HGF at 90% RH of 2.46±0.02 for NaCl, 2.35±0.02 for artifical SSA and 2.26±0.02 for natural SSA particles. Overall, these results suggest that the natural accumulation mode SSA particles produced in these experiments contained only a minor organic fraction, which had little effect on hygroscopic growth. Our measurement Correspondence to: Z. D. Ristovski (z.ristovski@qut.edu.au) of 8±6% is an order of magnitude below two previous measurements of the organic fraction in SSA particles of comparable sizes. We stress that our results were obtained using coastal seawater and they can't necessarily be applied on a regional or global ocean scale. Nevertheless, considering the order of magnitude discrepancy between this and previous studies, further research with independent measurement techniques and a variety of different seawaters is required to better quantify how much organic material is present in accumulation mode SSA.

Primary marine aerosol physical flux and chemical composition during a nutrient enrichment experiment in mesocosms in the Mediterranean Sea

“…The organic fraction measured in PM 1 does fall within the observed range of 30-80 % organic mass fractions from sea spray aerosol studies Facchini et al, 2008;Keene et al, 2007); however, marine organic mass fractions as low as 4 % (8 % volume) have also been observed (Modini et al, 2010), and the relevant biogeochemical parameters of the seawater influencing the organic fraction of sea spray are still debatable.…”

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

“…The mixing ratio of organic matter within the SS-OC type, due to its dominance in particles with D > 0.2 μm, exerts most of the organic mass variability in SSA overall. Prior studies have reported bulk organic mass fractions as high as 77-80% [Keene et al, 2007;Facchini et al, 2008] and as low as~4% [Modini et al, 2010] in SSA generated from natural seawater samples. The ensemble submicron organic mass fraction in these experiments was approximately 35-40% for periods Z1 and Z2 (Figure 6).…”

Direct aerosol chemical composition measurements to evaluate the physicochemical differences between controlled sea spray aerosol generation schemes

“…On the whole, the process of surfactant transport toward the air-sea interface would result in the accumulation of organic matter in the sea surface microlayer (SML) (Keene et al, 2007), which is a layer of material at the air-sea interface up to 1 mm thick that is typically highly enriched in dissolved and particulate organic material in the open ocean (Carlson, 1983;Liss and Duce, 1997;Aller et al, 2005;Cunliffe et al, 2011). Some sintered glass filter aerosol generators have been designed to mitigate the over-expression of organics in the SML by continuously refreshing the surface of the seawater subjected to bubbling (Keene et al, 2007;Modini et al, 2010;Bates et al, 2012); this design feature was not explicitly tested in this study. Wurl et al (2011) show that the SML exists on the ocean surface for wind speeds up to 10 m s −1 (global ocean mean wind speed is approximately 6 m s −1 ), so the existence of the SML is relevant for many instances of wave-induced bubble and foam production.…”

“…Recent reports indicate that pneumatic atomization does not produce particles of similar physical or chemical properties to those generated by bubble bursting (Fuentes et al, 2010b;Gaston et al, 2011). Until recently, two different bubble production techniques have been utilized for laboratory studies of aerosol composition: (1) air (or N 2 ) forced through sintered glass filters ("frits") (Cloke et al, 1991;Keene et al, 2007;Wise et al, 2009;Fuentes et al, 2010b;Modini et al, 2010;Park et al, 2014), and (2) impinging water jets (Facchini et al, 2008;Fuentes et al, 2010b;Hultin et al, 2010). A new approach introduced by produces SSA using reproducible breaking waves in a linear wave channel filled with natural, filtered seawater.…”