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.
Key Points
Organics in the Great Barrier Reef can influence sea spray aerosol composition
Coral reef sea spray aerosol can have a large nonvolatile organic fraction
Organic components in sea spray aerosol suppress water uptake
Volatile organic compounds (VOCs) in the headspace of bubble chambers containing branches of live coral in filtered reef seawater were analysed using gas chromatography with mass spectrometry ...(GC-MS). When the coral released mucus it was a source of dimethyl sulfide (DMS) and isoprene; however, these VOCs were not emitted to the chamber headspace from mucus-free coral. This finding, which suggests that coral is an intermittent source of DMS and isoprene, was supported by the observation of occasional large pulses of atmospheric DMS (DMS
a
) over Heron Island reef on the southern Great Barrier Reef (GBR), Australia, in the austral winter. The highest DMS
a
pulse (320 ppt) was three orders of magnitude less than the DMS mixing ratio (460 ppb) measured in the headspace of a dynamically purged bubble chamber containing a mucus-coated branch of
Acropora aspera
indicating that coral reefs can be strong point sources of DMS
a
. Static headspace GC-MS analysis of coral fragments identified mainly DMS and seven other minor reduced sulfur compounds including dimethyl disulfide, methyl mercaptan, and carbon disulfide, while coral reef seawater was an indicated source of methylene chloride, acetone, and methyl ethyl ketone. The VOCs emitted by coral and reef seawater are capable of producing new atmospheric particles < 15 nm diameter as observed at Heron Island reef. DMS and isoprene are known to play a role in low-level cloud formation, so aerosol precursors such as these could influence regional climate through a sea surface temperature regulation mechanism hypothesized to operate over the GBR.
Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei. Aerosols can cause a net cooling of climate by scattering sunlight ...and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes. Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases. However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere. It is thought that amines may enhance nucleation, but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid-amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid-dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.
Atmospheric new-particle formation affects climate and is one of the least understood atmospheric aerosol processes. The complexity and variability of the atmosphere has hindered elucidation of the ...fundamental mechanism of new-particle formation from gaseous precursors. We show, in experiments performed with the CLOUD (Cosmics Leaving Outdoor Droplets) chamber at CERN, that sulfuric acid and oxidized organic vapors at atmospheric concentrations reproduce particle nucleation rates observed in the lower atmosphere. The experiments reveal a nucleation mechanism involving the formation of clusters containing sulfuric acid and oxidized organic molecules from the very first step. Inclusion of this mechanism in a global aerosol model yields a photochemically and biologically driven seasonal cycle of particle concentrations in the continental boundary layer, in good agreement with observations.
The growth of freshly formed aerosol particles can be the bottleneck in their survival to cloud condensation nuclei. It is therefore crucial to understand how particles grow in the atmosphere. ...Insufficient experimental data has impeded a profound understanding of nano-particle growth under atmospheric conditions. Here we study nano-particle growth in the CLOUD (Cosmics Leaving OUtdoors Droplets) chamber, starting from the formation of molecular clusters. We present measured growth rates at sub-3 nm sizes with different atmospherically relevant concentrations of sulphuric acid, water, ammonia and dimethylamine. We find that atmospheric ions and small acid-base clusters, which are not generally accounted for in the measurement of sulphuric acid vapour, can participate in the growth process, leading to enhanced growth rates. The availability of compounds capable of stabilizing sulphuric acid clusters governs the magnitude of these effects and thus the exact growth mechanism. We bring these observations into a coherent framework and discuss their significance in the atmosphere.
Traffic-related aerosol particles are ubiquitous in the urban atmosphere. As they are produced at ground level, they can also cause adverse health effects to urban dwellers. However, knowledge of the ...formation, transformation and chemically resolved size distribution of urban ultrafine particles is incomplete. Thus, more of these measurements are needed for better assessment of ambient air quality and its potential health effects. The particle number concentration, aerosol black carbon (BC) concentration and size distribution of traffic-related aerosols were measured near two major roads in Kuopio, Finland, from 16 June to 5 July, 2004. Furthermore, the properties of roadside aerosol particles were examined with the Tandem Differential Mobility Analyzer technique (TDMA). A suite of TDMA instruments relying on water (hygroscopic TDMA) and ethanol (organic TDMA) condensation as well as heating (volatility TDMA) were deployed to study the composition of the nucleation and Aitken mode particles (
D
p = 10–50 nm) formed from vehicle exhaust. The results show that a simple three-component model was able to reproduce characteristic insoluble, organic and water-soluble volume fractions. Insoluble constituents were dominant in the Aitken mode particles, whereas organic compounds dominated the nucleation mode sizes. On average, only a small volume fraction was water-soluble, but a clear external mixing was observed particularly when enough time was allowed after the tail pipe emissions. The contribution of the insoluble material was seen to increase as a function of particle size, being typically less than 10% at 10 nm and between 20 and 50% at 50 nm, in contrast to the organic fraction, which decreased from about 80% at nucleation mode size range to 50–60% at 50 nm.
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