Sea spray aerosol in the Great Barrier Reef and the presence of nonvolatile organics

Abstract

Sea spray aerosol (SSA) particles produced from the ocean surface in regions of biological activity can vary greatly in size, number and composition, and in their influence on cloud formation. Algal species such as phytoplankton can alter the SSA composition. Numerous studies have investigated nascent SSA properties, but all of these have focused on aerosol particles produced by seawater from noncoral related phytoplankton and in coastal regions. Bubble chamber experiments were performed with seawater samples taken from the reef flat around Heron Island in the Great Barrier Reef during winter 2011. Here we show that the SSA from these samples was composed of an internal mixture of varying fractions of sea salt, semivolatile organics, as well as nonvolatile (below 550°C) organics. A relatively constant volume fraction of semivolatile organics of 10%–13% was observed, while nonvolatile organic volume fractions varied from 29% to 49% for 60 nm SSA. SSA organic fractions were estimated to reduce the activation ratios of SSA to cloud condensation nuclei by up to 14% when compared with artificial sea salt. Additionally, a sea‐salt calibration was applied so that a compact time‐of‐flight aerosol mass spectrometer could be used to quantify the contribution of sea salt to submicron SSA, which yielded organic volume fractions of 3%–6%. Overall, these results indicate a high fraction of organics associated with wintertime Aitken mode SSA generated from Great Barrier Reef seawater. Further work is required to fully distinguish any differences coral reefs have on SSA composition when compared to open oceans.

Sea spray aerosol organic enrichment, water uptake and surface tension effects

“…Atlantic oceans (less than 15% volatilised at below 230 • C), and in the Great Barrier Reef (Bates et al, 2012;Mallet et al, 2016;Quinn et al, 2014), our observations are broadly consistent with these results. It should be noted that a non-volatile SSA fraction is not universally observed (Modini et al, 2010a;O'Dowd et al, 2004;Ovadnevaite et al, 2011b).…”

“…Modini et al, 2010a). This approach quantifies the proportion of volatility due to the presence of hydrates and due to the presence of organics, and is therefore an improvement on previously published estimates of the SSA OVF (Mallet et al, 2016;Modini et al, 2010a;Quinn et al, 2014).…”

“…For example Fuentes et al (2010) fitted lognormal modes with mean mobility diameters of 20, 41, 87 and 250 nm to laboratory sea salt generated using glass sintered filters, and modes with mean mobility diameters of 14, 48, 124 and 334 nm for plunging water generated sea salt. SSA produced from sintered glass filters does not perfectly represent real world bubble bursting from wave breaking (Collins et al, 2014;Prather et al, 2013) but the use of four glass filters with different pore sizes resulted in a broader distribution than other measurements of nascent SSA using glass filters (Collins et al, 2014;Fuentes et al, 2010;Keene et al, 2007;Mallet et al, 2016). Observations have shown organic enrichment (King et al, 2013) and also externally mixed organics (Collins et al, 2014) for Aitken and accumulation mode SSA using sintered glass techniques, with slightly higher organic enrichment than that observed using plunging water or wave breaking methods.…”

“…Table S1 provides a description of the seawater samples that were taken. Nascent SSA was generated in-situ in a 0.45 m 3 cylindrical polytetrafluoroethylene chamber housing four sintered glass filters with porosities between 16 and 250 µm (Cravigan, 2015;Mallet et al, 2016). Dried and filtered compressed air was passed through the glass filters at a flow rate of 15.5 ± 3 L min −1 and resulting SSA was sampled from the headspace of the chamber.…”

Overview and preliminary results of the Surface Ocean Aerosol Production (SOAP) campaign

“…Particle size distribution and concentration, including ultrafine nuclei concentrations, were continuously monitored using a scanning mobility particle sizer (SMPS) and optical particle counters (OPCs), with bulk ion chemistry samples collected using a high-volume sampler. The composition of primary marine aerosols was also examined using a 0.45 m 3 bubble chamber, in which sea spray was formed via the bursting of bubbles produced by passing clean compressed air through sintered glass (Mallet et al, 2016).…”