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

Abstract

AbstractSea 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.