On the Source and Composition of Cloud Nuclei in a Subsident Air Mass over the North Atlantic
01 Aug 1970-Journal of the Atmospheric Sciences (American Meteorological Society)-Vol. 27, Iss: 5, pp 791-797
TL;DR: In this article, the concentration of cloud nuclei, which are activated at a supersaturation of 0.75%, were made aboard an aircraft at various altitudes in a subsident air mass over the North Atlantic Ocean and on the cast coast of Barbados, West Indies.
Abstract: Measurements of the concentration of cloud nuclei, which are activated at a supersaturation of 0.75%, were made aboard an aircraft at various altitudes in a subsident air mass over the North Atlantic Ocean and on the cast coast of Barbados, West Indies. The measurements were made on air samples at normal temperatures as well as on air samples heated to various temperatures up to 600C. In this way the volatility of the cloud nuclei was compared to the volatility as measured in a similar manner in the laboratory on nuclei artificially generated and of a known composition. The measurements at Barbados showed that ∼50% of the cloud nuclei were nonvolatile at the temperatures used and thus were similar to artificially generated nuclei composed of sea salt; the remaining nuclei were destroyed by temperatures ≳320C. The aircraft measurements showed the fraction of volatile cloud nuclei to increase with altitude with all nuclei being volatile above the inversion layer. These measurements indicate that in...
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09 Jan 2004
TL;DR: In this paper, Sea salt aerosol (SSA) particles interact with other atmospheric gaseous and aerosol constituents by acting as sinks for condensable gases and suppressing new particle formation, thus influencing the size distribution of other aerosols and more broadly influencing the geochemical cycles of substances with which they interact.
Abstract: Sea salt aerosol (SSA) exerts a major influence over a broad reach of geophysics. It is important to the physics and chemistry of the marine atmosphere and to marine geochemistry and biogeochemistry generally. It affects visibility, remote sensing, atmospheric chemistry, and air quality. Sea salt aerosol particles interact with other atmospheric gaseous and aerosol constituents by acting as sinks for condensable gases and suppressing new particle formation, thus influencing the size distribution of these other aerosols and more broadly influencing the geochemical cycles of substances with which they interact. As the key aerosol constituent over much of Earth's surface at present, and all the more so in pre-industrial times, SSA is central to description of Earth's aerosol burden.
603 citations
TL;DR: In this paper, the authors studied the effect of pollution on global climate and found that the climate effect is comparable to that of increased carbon dioxide, and acts in the opposite direction, in that increasing absorption also attends increasing pollution.
Abstract: Increased pollution leads to increasing particulate concentrations. Since some particles nucleatedrop formation, clouds will contain, with increasing pollution, more drops per unit volume, andhence will tend to be optically thicker and more reflecting. An opposite effect is also present, inthat increasing absorption also attends increasing pollution. Measurements suggest that theformer (brightening) effect is the dominant one for global climate and that the climatic effect isquite comparable to that of increased carbon dioxide, and acts in the opposite direction. DOI: 10.1111/j.1600-0889.1984.tb00254.x
584 citations
TL;DR: The results indicate that a dimethyl sulphide biological control over cloud condensation nuclei probably does not exist and that sources of these nuclei to the marine boundary layer and the response of clouds to changes in aerosol are much more complex than was recognized twenty years ago.
Abstract: The CLAW hypothesis advanced the idea of biological regulation of Earth's climate. In the proposed feedback loop, cloud condensation nuclei and cloud albedo are regulated up or down by oceanic phytoplankton through the medium of dimethyl sulphide emissions, such that climate remains moderate. CLAW, named after the authors of the Nature article that introduced it in 1987 (Charlson, Lovelock, Andreae and Warren, see go.nature.com/alfv2n
), proved influential and spawned two decades of intensive research investigating the required mechanisms. Patricia Quinn and Timothy Bates have now synthesized this sprawling field and argue that there is no strong evidence to support any of the critical steps required by CLAW. Instead, contributions by organic and non-organic compounds suggest a far more complex reality. More than twenty years ago, a biological regulation of climate was proposed whereby emissions of dimethyl sulphide from oceanic phytoplankton resulted in the formation of aerosol particles that acted as cloud condensation nuclei in the marine boundary layer. In this hypothesis—referred to as CLAW—the increase in cloud condensation nuclei led to an increase in cloud albedo with the resulting changes in temperature and radiation initiating a climate feedback altering dimethyl sulphide emissions from phytoplankton. Over the past two decades, observations in the marine boundary layer, laboratory studies and modelling efforts have been conducted seeking evidence for the CLAW hypothesis. The results indicate that a dimethyl sulphide biological control over cloud condensation nuclei probably does not exist and that sources of these nuclei to the marine boundary layer and the response of clouds to changes in aerosol are much more complex than was recognized twenty years ago. These results indicate that it is time to retire the CLAW hypothesis.
543 citations
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...Refractory species, including dust, sea salt and large organic polymers, must be heated to over 600 °C for thermal decomposition to occu...
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TL;DR: In this article, measurements and analyses of the aerosol size distributions and optical properties found in the marine boundary layer (MBL) during the 1983 USNS Lynch cruise from Charleston, South Carolina, to Scotland via Canary Islands are presented.
Abstract: Measurements and analyses of the aerosol size distributions and optical properties found in the marine boundary layer (MBL) during the 1983 USNS Lynch cruise from Charleston, South Carolina, to Scotland via Canary Islands are presented. The data given are the most extensive and accurate measurements of the submicron marine aerosol size distribution to date and are supplemented by extensive meteorological observations. Eight detailed case studies of the evolution of the size distribution that occurred under different meteorological conditions are presented and discussed. The data indicate that repeated cycling of MBL air through nonprecipitating clouds at the top of the MBL is a major factor in shaping the size distribution and that new particle formation by heteromolecular, homogeneous nucleation is the most likely mechanism for sustaining the particle concentration below 0.04-μm radius. Calculations of the scattering and extinction coefficients and optical depth of the MBL as a function of wavelength directly from the measured size distribution and MBL vertical structure are compared to measured values of the scattering coefficient and optical depth. These measured and calculated optical properties correlate well throughout the cruise and the results give a relatively consistent picture of the relationship between the aerosol size distribution and electromagnetic properties in the MBL.
451 citations
TL;DR: In this article, the authors examined the physicochemical characteristics of submicron aerosol particles over the Northeast Atlantic during October/November 1989 using a thermal analytical technique and are classified according to 10 air mass origin.
Abstract: Physicochemical characteristics of submicron aerosol particles over the Northeast Atlantic (63[degrees]N, 8[degrees]W) during October/November 1989 have been examined using a thermal analytical technique and are classified according 10 air mass origin. Aerosol associated with anthropogenically influenced air masses contained typically 80% sulphate particles by number, the remainder being soot carbon and sea salt. For Arctic air masses the contribution of sulphate to the total aerosol was reduced to around 65%, due to low concentrations relative 10 sea salt which is dependent on wind speed. In situations with clean maritime air and high wind speeds, sulphate aerosol accounted for less than 25% of the total accumulation mode particles, the remainder consisting predominantly of sea salt. Arctic air masses and clean maritime air during periods of high winds were consistently acidic with inferred molar ratios of NH[sub 4][sup +]/SO[sub 4][sup =] near 0.2. The continental and modified maritime aerosol encountered was found to have molar ratios of about 0.8. Soot carbon was present in all air masses to a similar degree (5-13%). In clean air masses, submicron sea salt aerosol concentrations showed a strong exponential increase with wind speed (correlation coefficients cc [ge] 0.8), down to a dry particle radius of 0.05more » [mu]m. Under these clean air' conditions and high winds the sea salt aerosol dominated all particle sizes for r > 0.05 [mu]m and accounted for approximately 75% of the total concentration, suggesting that under these conditions, sea salt aerosol would comprise the primary source cloud condensation nuclei (CCN) in stratiform clouds. 30 refs., 8 figs., 4 tabs.« less
359 citations