Sea-salt particles and the CLAW hypothesis

Smith, Michael H.

doi:10.1071/en07071

Cited by 14 publications

(9 citation statements)

References 53 publications

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“…Sea salt particles have the necessary properties to act very efficiently as CCN. [105,106] Other work confirms the role of sea salt as CCN, [107,108] with sea salt particles representing between 5 and 90% of CCN in the MBL. [109] It is now possible to directly measure the flux of sea salt from the surface of the ocean [110] and this along with laboratory studies of breaking bubbles [111] is improving the understanding of the relative contribution of sea salt to CCN number concentrations.…”

Section: Feedbacksmentioning

confidence: 56%

The CLAW hypothesis: a review of the major developments

2007

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Environmental context. Understanding the role of clouds in the warming and the cooling of the planet and how that role alters in a warming world is one of the biggest uncertainties climate change researchers face. Important in this regard is the influence on cloud properties of cloud condensation nuclei, the tiny atmospheric particles necessary for the nucleation of every single cloud droplet. The anthropogenic contribution to cloud condensation nuclei is known to be large in some regions through knowledge of pollutant emissions; however, the natural processes that regulate cloud condensation nuclei over large parts of the globe are less well understood. The CLAW hypothesis provides a mechanism by which plankton may modify climate through the atmospheric sulfur cycle via the provision of sulfate cloud condensation nuclei. The CLAW hypothesis was published over 20 years ago and has stimulated a great deal of research.Abstract. The CLAW hypothesis has for 20 years provided the intriguing prospect of oceanic and atmospheric systems exhibiting in an intimately coupled way a capacity to react to changing climate in a manner that opposes the change. A great number of quality scientific papers has resulted, many confirming details of specific links between oceanic phytoplankton and dimethylsulfide (DMS) emission to the atmosphere, the importance of DMS oxidation products in regulation of marine atmospheric cloud condensation nucleus (CCN) populations, and a concomitant influence on marine stratocumulus cloud properties. However, despite various links in the proposed phytoplankton-DMS-CCN-cloud albedo climate feedback loop being affirmed, there has been no overall scientific synthesis capable of adequately testing the hypothesis at a global scale. Moreover, significant gaps and contradictions remain, such as a lack of quantitative understanding of new particle formation processes in the marine atmospheric boundary layer, and of the extent to which dynamical, rather than microphysical, cloud feedbacks exist. Nevertheless, considerable progress has been made in understanding 'Earth System Science' involving the integration of ocean and atmospheric systems inherent in the CLAW hypothesis. We present here a short review of this progress since the publication of the CLAW hypothesis.

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Section: Feedbacksmentioning

confidence: 56%

The CLAW hypothesis: a review of the major developments

2007

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“…Uncertainties still exist in the quantification of the influence of DMS on climate in a future climate scenario. Recent works (Yoon and Brimblecombe, 2002;Pierce and Adams, 2006;Smith, 2007) have shown that the sea salt aerosols play a role in marine CCN production. Further improvements are needeed to include sea salt in a wide range of size distribution realistically to quantify the role of DMS-sea salt interactions in global climate models.…”

Section: Discussionmentioning

confidence: 99%

Quantification of DMS aerosol-cloud-climate interactions using the ECHAM5-HAMMOZ model in a current climate scenario

et al. 2010

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The contribution of ocean dimethyl sulfide (DMS) emissions to changes in cloud microphysical properties is quantified seasonally and globally for present day climate conditions using an aerosol-chemistry-climate general circulation model, ECHAM5-HAMMOZ, coupled to a cloud microphysics scheme. We evaluate DMS aerosol-cloud-climate linkages over the southern oceans where anthropogenic influence is minimal. The changes in the number of activated particles, cloud droplet number concentration (CDNC), cloud droplet effective radius, cloud cover and the radiative forcing are examined by analyzing two simulations: a baseline simulation with ocean DMS emissions derived from a prescribed climatology and one in which the ocean DMS emissions are switched off. Our simulations show that the model realistically simulates the seasonality in the number of activated particles and CDNC, peaking during Southern Hemisphere (SH) summer coincident with increased phytoplankton blooms and gradually declining with a minimum in SH winter. In comparison to a simulation with no DMS, the CDNC level over the southern oceans is 128% larger in the baseline simulation averaged over the austral summer months. Our results also show an increased number of smaller sized cloud droplets during this period. We estimate a maximum decrease of up to 15–18% in the droplet radius and a mean increase in cloud cover by around 2.5% over the southern oceans during SH summer in the simulation with ocean DMS compared to when the DMS emissions are switched off. The global annual mean top of the atmosphere DMS aerosol all sky radiative forcing is −2.03 W/m2, whereas, over the southern oceans during SH summer, the mean DMS aerosol radiative forcing reaches −9.32 W/m2

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“…The FN parameterization is one of the most (Fountoukis and Nenes, 2005). In addition to treating the competition among all modes, the FN parameterization can also include the presence of surfactants and slightly soluble species (Shulman et al, 1996;Laaksonen et al, 1998). The FN parameterization includes a size-dependent mass transfer coefficient for the growth of water droplets to accommodate the effect of size (and potentially organic films) on the droplet growth rate.…”

Section: Aerosol Activation Parameterizationmentioning

confidence: 99%

Global distribution and climate forcing of marine organic aerosol: 1. Model improvements and evaluation

et al. 2011

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Marine organic aerosol emissions have been implemented and evaluated within the National Center of Atmospheric Research (NCAR)'s Community Atmosphere Model (CAM5) with the Pacific Northwest National Laboratory's 7-mode Modal Aerosol Module (MAM-7). Emissions of marine primary organic aerosols (POA), phytoplankton-produced isoprene- and monoterpenes-derived secondary organic aerosols (SOA) and methane sulfonate (MS−) are shown to affect surface concentrations of organic aerosols in remote marine regions. Global emissions of submicron marine POA is estimated to be 7.9 and 9.4 Tg yr−1, for the Gantt et al. (2011) and Vignati et al. (2010) emission parameterizations, respectively. Marine sources of SOA and particulate MS− (containing both sulfur and carbon atoms) contribute an additional 0.2 and 5.1 Tg yr−1, respectively. Widespread areas over productive waters of the Northern Atlantic, Northern Pacific, and the Southern Ocean show marine-source submicron organic aerosol surface concentrations of 100 ng m−3, with values up to 400 ng m−3 over biologically productive areas. Comparison of long-term surface observations of water insoluble organic matter (WIOM) with POA concentrations from the two emission parameterizations shows that despite revealed discrepancies (often more than a factor of 2), both Gantt et al. (2011) and Vignati et al. (2010) formulations are able to capture the magnitude of marine organic aerosol concentrations, with the Gantt et al. (2011) parameterization attaining better seasonality. Model simulations show that the mixing state of the marine POA can impact the surface number concentration of cloud condensation nuclei (CCN). The largest increases (up to 20%) in CCN (at a supersaturation (S) of 0.2%) number concentration are obtained over biologically productive ocean waters when marine organic aerosol is assumed to be externally mixed with sea-salt. Assuming marine organics are internally-mixed with sea-salt provides diverse results with increases and decreases in the concentration of CCN over different parts of the ocean. The sign of the CCN change due to the addition of marine organics to sea-salt aerosol is determined by the relative significance of the increase in mean modal diameter due to addition of mass, and the decrease in particle hygroscopicity due to compositional changes in marine aerosol. Based on emerging evidence for increased CCN concentration over biologically active surface ocean areas/periods, our study suggests that treatment of sea spray in global climate models (GCMs) as an internal mixture of marine organic aerosols and sea-salt will likely lead to an underestimation in CCN number concentration

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Sea-salt particles and the CLAW hypothesis

Cited by 14 publications

References 53 publications

The CLAW hypothesis: a review of the major developments

The CLAW hypothesis: a review of the major developments

Quantification of DMS aerosol-cloud-climate interactions using the ECHAM5-HAMMOZ model in a current climate scenario

Global distribution and climate forcing of marine organic aerosol: 1. Model improvements and evaluation

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