On the effect of dust particles on global cloud condensation nuclei and cloud droplet number

Karydis, Vlassis A.; Kumar, Prashant; Barahona, D.; Sokolik, I. N.; Nenes, Athanasios

doi:10.1029/2011jd016283

Cited by 182 publications

(186 citation statements)

References 121 publications

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“…This is in line with Twohy et al (2009), who also found that dust arriving at the Cape Verde Islands had acted as CCN in trade wind cumuli. It also agrees with Karydis et al (2011), who show that mineral dust particles contribute significantly to CCN number concentrations, particularly in outflow regions of deserts, which, as shown here, might extend at least as far as Barbados for the Sahara. Not all air masses originating from Africa carried continental particles in such large numbers.…”

Section: Discussion Of the Different Aerosol Typessupporting

confidence: 78%

“…Accumulation type aerosol was connected to long-range transport from the Sahara and Sahel region, where either mineral dust from the desert and/or biomass-burning particles from the Sahel were involved in raising the particle number concentrations in the accumulation mode. Although particles from both biomass burning and mineral dust are sometimes assumed to be of rather insoluble nature, they have been shown to contribute to CCN (Engelhart et al, 2012;Twohy et al, 2009;Karydis et al, 2011), and an increase in N CCN due to their presence was also observed in the present study.…”

Section: Discussionsupporting

confidence: 62%

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Aerosol arriving on the Caribbean island of Barbados: physical properties and origin

et al. 2016

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Abstract. The marine aerosol arriving at Barbados (Ragged Point) was characterized during two 3-week long measurement periods in November 2010 and April 2011, in the context of the measurement campaign CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArbados). Through a comparison between groundbased and airborne measurements it was shown that the former are representative of the marine boundary layer at least up to cloud base. In general, total particle number concentrations (N total ) ranged from as low as 100 up to 800 cm −3 , while number concentrations for cloud condensation nuclei (N CCN ) at a supersaturation of 0.26 % ranged from some 10 to 600 cm −3 . N total and N CCN depended on the air mass origin. Three distinct types of air masses were found. One type showed elevated values for both N total and N CCN and could be attributed to long-range transport from Africa, by which biomass burning particles from the Sahel region and/or mineral dust particles from the Sahara were advected. The second and third type both had values for N CCN below 200 cm −3 and a clear minimum in the particle number size distribution (NSD) around 70 to 80 nm (Hoppel minimum). While for one of these two types the accumulation mode was dominating (albeit less so than for air masses advected from Africa), the Aitken mode dominated the other and contributed more than 50 % of all particles. These Aitken mode particles likely were formed by new particle formation no more than 3 days prior to the measurements. Hygroscopicity of particles in the CCN size range was determined from CCN measurements to be κ = 0.66 on average, which suggests that these particles contain mainly sulfate and do not show a strong influence from organic material, which might generally be the case for the months during which measurements were made. The average κ could be used to derive N CCN from measured number size distributions, showing that this is a valid approach to obtain N CCN . Although the total particulate mass sampled on filters was found to be dominated by Na + and Cl − , this was found to be contributed by a small number of large particles (> 500 nm, mostly even in the super-micron size range). Based on a three-modal fit, a sea spray mode observed in the NSDs was found to contribute 90 % to the total particulate mass but only 4 to 10 % to N total and up to 15 % to N CCN . This is in accordance with finding no correlation between N total and wind speed.

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Section: Discussion Of the Different Aerosol Typessupporting

confidence: 78%

Section: Discussionsupporting

confidence: 62%

Aerosol arriving on the Caribbean island of Barbados: physical properties and origin

et al. 2016

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“…The annually and spatially averaged occurrence frequency of NLLJs is similar in and the atmospheric circulation (e.g. Sokolik and Toon 1996;Rosenfeld et al 2001;Lohmann and Feichter 2005;Tompkins et al 2005;Karydis et al 2011;Schmechtig et al 2011). In addition to these climate effects, suspended dust aerosol decreases the air quality with adverse influences on human health (e.g.…”

Section: Introductionmentioning

confidence: 93%

A process-based evaluation of dust-emitting winds in the CMIP5 simulation of HadGEM2-ES

et al. 2015

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Medium-Range Weather Forecasts. Compared to ERAInterim, a stronger pressure ridge over northern Africa in winter and the southward displaced heat low in summer result in differences in location and strength of NLLJs. Particularly the larger geostrophic winds associated with the stronger ridge have a strengthening effect on NLLJs over parts of West Africa in winter. Stronger NLLJs in summer may rather result from an artificially increased mixing coefficient under stable stratification that is weaker in HadGEM2-ES. NLLJs in the Bodélé Depression are affected by stronger synoptic-scale pressure gradients in HadGEM2-ES. Wintertime geostrophic winds can even be so strong that the associated vertical wind shear prevents the formation of NLLJs. These results call for further model improvements in the synoptic-scale dynamics and the physical parametrization of the nocturnal stable boundary layer to better represent dust-emitting processes in the atmospheric model. The new approach could be used for identifying systematic behavior in other models with respect to meteorological processes for dust emission. This would help to improve dust emission simulations and contribute to decreasing the currently large uncertainty in climate change projections with respect to dust aerosol.

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“…Note that deriving monthly-mean CDNC from monthly-mean sizeresolved particle concentrations and monthly-mean particle composition fields does not account for temporal variations in aerosol properties. However, our approach and our choice of updraught velocities have been shown to provide a good approximation of mean CDNC (Fountoukis et al, 2007;Pringle et al, 2009;Karydis et al, 2011). As with many other aerosol activation schemes (e.g., Chen and Penner, 2005;Roelofs et al, 2006), the employed scheme does not account for droplet collision-coalescence (i.e.…”

Section: Treatment Of Aerosol Activation and Model Evaluationmentioning

confidence: 99%

Importance of tropospheric volcanic aerosol for indirect radiative forcing of climate

et al. 2012

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Abstract.Observations and models have shown that continuously degassing volcanoes have a potentially large effect on the natural background aerosol loading and the radiative state of the atmosphere. We use a global aerosol microphysics model to quantify the impact of these volcanic emissions on the cloud albedo radiative forcing under pre-industrial (PI) and present-day (PD) conditions. We find that volcanic degassing increases global annual mean cloud droplet number concentrations by 40 % under PI conditions, but by only 10 % under PD conditions. Consequently, volcanic degassing causes a global annual mean cloud albedo effect of −1.06 W m −2 in the PI era but only −0.56 W m −2 in the PD era. This non-equal effect is explained partly by the lower background aerosol concentrations in the PI era, but also because more aerosol particles are produced per unit of volcanic sulphur emission in the PI atmosphere. The higher sensitivity of the PI atmosphere to volcanic emissions has an important consequence for the anthropogenic cloud radiative forcing because the large uncertainty in volcanic emissions translates into an uncertainty in the PI baseline cloud radiative state. Assuming a −50/+100 % uncertainty range in the volcanic sulphur flux, we estimate the annual mean anthropogenic cloud albedo forcing to lie between −1.16 W m −2 and −0.86 W m −2 . Therefore, the volcanically induced uncertainty in the PI baseline cloud radiative state substantially adds to the already large uncertainty in the magnitude of the indirect radiative forcing of climate.

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On the effect of dust particles on global cloud condensation nuclei and cloud droplet number

Cited by 182 publications

References 121 publications

Aerosol arriving on the Caribbean island of Barbados: physical properties and origin

Aerosol arriving on the Caribbean island of Barbados: physical properties and origin

A process-based evaluation of dust-emitting winds in the CMIP5 simulation of HadGEM2-ES

Importance of tropospheric volcanic aerosol for indirect radiative forcing of climate

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