Assessing the Impact of Mineral Dust and Adsorption Activation on Cloud Droplet Formation

Abstract. The importance of wind-blown mineral dust for cloud droplet formation is studied by considering i) the adsorption of water on the surface of insoluble particles, ii) the particle coating by soluble material (due to atmospheric aging) which augments cloud condensation nuclei (CCN) activity, and iii) the effect of dust on inorganic aerosol concentrations through thermodynamic interactions with mineral cations. The ECHAM5/MESSy Atmospheric Chemistry (EMAC) model is used to simulate the composition of global atmospheric aerosol; the ISORROPIA-II thermodynamic equilibrium model treats the interactions of K+-Ca2+-Mg2+-NH4+-Na+-SO42−-NO3−-Cl−-H2O aerosol with gas-phase inorganic constituents. Dust is considered a mixture of inert material with reactive minerals; emissions are calculated online by taking into account the soil particle size distribution and chemical composition of different deserts worldwide. The impact of dust on droplet formation is treated through the "unified dust activation parameterization" that considers the inherent hydrophilicity from adsorption and acquired hygroscopicity from soluble salts during aging. Our simulations suggest that the presence of dust increases cloud droplet number concentrations (CDNC) over major deserts (e.g., up to 20 % over the Sahara and Taklimakan Deserts) and decreases CDNC over polluted areas (e.g., up to 10 % over southern Europe and 20 % over northeastern Asia). This leads to a global net decrease of CDNC by 11 %. The adsorption activation of insoluble aerosols and the mineral dust chemistry are shown to be equally important for the cloud droplet formation over the main desserts, e.g., by considering these effects CDNC increases by 20 % over the Sahara. Remote from deserts the application of adsorption theory is critically important since the increased water uptake by the large aged dust particles (i.e., due to the added hydrophilicity by the soluble coating) reduce the maximum supersaturation and thus the cloud droplet formation from the smaller anthropogenic particles (e.g., CDNC decreases by 10 % over southern Europe and 20 % over northeastern Asia by applying adsorption theory). The global average CDNC decreases by 10 % by considering adsorption activation, while changes are negligible when accounting for the mineral dust chemistry. Sensitivity simulations indicate that CDNC is also sensitive to the mineral dust mass and inherent hydrophilicity, and not to the chemical composition of the emitted dust.

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Is a more physical representation of aerosol activation needed for simulations of fog?

10.5194/acp-2020-904 ◽

2020 ◽

Author(s):

Craig Poku ◽

Andrew N. Ross ◽

Adrian A. Hill ◽

Alan M. Blyth ◽

Ben Shipway

Keyword(s):

Climate Models ◽

Thick Layer ◽

Cloud Droplet ◽

Droplet Formation ◽

Number Concentration ◽

Radiation Fog ◽

Simple Method ◽

Physically Based ◽

Aerosol Activation ◽

The Impact

Abstract. Aerosols play a crucial role in the fog life cycle, as they determine the droplet number concentration, and hence droplet size, which in turn controls both the fog's optical thickness and life span. Detailed aerosol-microphysics schemes which accurately represent droplet formation and growth are unsuitable for weather forecasting and climate models, as the computational power required to calculate droplet formation would dominate the treatment of the rest of the physics in the model. A simple method to account for droplet formation is the use of an aerosol activation scheme, which parameterises the droplet number concentration based on a change in supersaturation at a given time. Traditionally, aerosol activation parameterisation schemes were designed for convective clouds and assume that supersaturation is reached through adiabatic lifting, with many imposing a minimum vertical velocity (e.g. 0.1 m/s) to account for unresolved sub-grid ascent. In radiation fog, the measured updrafts during initial formation are often insignificant, with radiative cooling being the dominant process leading to saturation. As a result, there is a risk that many aerosol activation schemes will overpredict the initial fog number concentration, which in turn may result in the fog transitioning to an optically thick layer too rapidly. This paper presents a more physically-based aerosol activation scheme that can account for a change in saturation due to non-adiabatic processes. Using an offline model, our results show that the minimum updraft velocity threshold assumption can overpredict the droplet number by up to 70 % in comparison to a cooling rate found in fog formation. The new scheme has been implemented in the Met Office Natural Environment Research Council (NERC) Cloud (MONC) LES model, and tested using observations of a radiation fog case study based in Cardington, UK. The results in this work show that using a more physically-based method of aerosol activation leads to the calculation of a more appropriate cloud droplet number. As a result, there is a slower transition to an optically thick (well-mixed) fog that is more in-line with observations. The results shown in this paper demonstrate the importance of aerosol activation representation in fog modelling, and the impact that the cloud droplet number has on processes linked to the formation and development of radiation fog. Unlike the previous parameterisation for aerosol activation, the revised scheme is suitable to simulate aerosol activation in both fog and convective cloud regimes.

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CCN Ability of Asian Mineral Dust Particles and Their Effects on Cloud Droplet Formation

Journal of the Meteorological Society of Japan Ser II ◽

10.2151/jmsj.2011-512 ◽

2011 ◽

Vol 89 (5) ◽

pp. 581-587 ◽

Cited By ~ 18

Author(s):

Katsuya YAMASHITA ◽

Masataka MURAKAMI ◽

Akihiro HASHIMOTO ◽

Takuya TAJIRI

Keyword(s):

Mineral Dust ◽

Cloud Droplet ◽

Droplet Formation ◽

Dust Particles

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Global impact of mineral dust on cloud droplet number concentration

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-5601-2017 ◽

2017 ◽

Vol 17 (9) ◽

pp. 5601-5621 ◽

Cited By ~ 30

Author(s):

Vlassis A. Karydis ◽

Alexandra P. Tsimpidi ◽

Sara Bacer ◽

Andrea Pozzer ◽

Athanasios Nenes ◽

...

Keyword(s):

Chemical Composition ◽

Mineral Dust ◽

Cloud Droplet ◽

Droplet Formation ◽

Number Concentration ◽

Dust Particles ◽

Southern Europe ◽

Northeastern Asia ◽

Adsorption Theory ◽

Cloud Droplet Number Concentration

Abstract. The importance of wind-blown mineral dust for cloud droplet formation is studied by considering (i) the adsorption of water on the surface of insoluble particles, (ii) particle coating by soluble material (atmospheric aging) which augments cloud condensation nuclei (CCN) activity, and (iii) the effect of dust on inorganic aerosol concentrations through thermodynamic interactions with mineral cations. The ECHAM5/MESSy Atmospheric Chemistry (EMAC) model is used to simulate the composition of global atmospheric aerosol, while the ISORROPIA-II thermodynamic equilibrium model treats the interactions of K+-Ca2+-Mg2+-NH4+-Na+-SO42−-NO3−-Cl−-H2O aerosol with gas-phase inorganic constituents. Dust is considered a mixture of inert material with reactive minerals and its emissions are calculated online by taking into account the soil particle size distribution and chemical composition of different deserts worldwide. The impact of dust on droplet formation is treated through the unified dust activation parameterization that considers the inherent hydrophilicity from adsorption and acquired hygroscopicity from soluble salts during aging. Our simulations suggest that the presence of dust increases cloud droplet number concentration (CDNC) over major deserts (e.g., up to 20 % over the Sahara and the Taklimakan desert) and decreases CDNC over polluted areas (e.g., up to 10 % over southern Europe and 20 % over northeastern Asia). This leads to a global net decrease in CDNC by 11 %. The adsorption activation of insoluble aerosols and the mineral dust chemistry are shown to be equally important for the cloud droplet formation over the main deserts; for example, these effects increase CDNC by 20 % over the Sahara. Remote from deserts the application of adsorption theory is critically important since the increased water uptake by the large aged dust particles (i.e., due to the added hydrophilicity by the soluble coating) reduce the maximum supersaturation and thus cloud droplet formation from the relatively smaller anthropogenic particles (e.g., CDNC decreases by 10 % over southern Europe and 20 % over northeastern Asia by applying adsorption theory). The global average CDNC decreases by 10 % by considering adsorption activation, while changes are negligible when accounting for the mineral dust chemistry. Sensitivity simulations indicate that CDNC is also sensitive to the mineral dust mass and inherent hydrophilicity, and not to the chemical composition of the emitted dust.

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Is a more physical representation of aerosol activation needed for simulations of fog?

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-7271-2021 ◽

2021 ◽

Vol 21 (9) ◽

pp. 7271-7292

Author(s):

Craig Poku ◽

Andrew N. Ross ◽

Adrian A. Hill ◽

Alan M. Blyth ◽

Ben Shipway

Keyword(s):

Cooling Rate ◽

Thick Layer ◽

Cloud Droplet ◽

Droplet Formation ◽

Number Concentration ◽

Radiation Fog ◽

Simple Method ◽

Physically Based ◽

Aerosol Activation ◽

The Impact

Abstract. Aerosols play a crucial role in the fog life cycle, as they determine the droplet number concentration and hence droplet size, which in turn controls both the fog's optical thickness and lifespan. Detailed aerosol-microphysics schemes which accurately represent droplet formation and growth are unsuitable for weather forecasting and climate models, as the computational power required to calculate droplet formation would dominate the treatment of the rest of the physics in the model. A simple method to account for droplet formation is the use of an aerosol activation scheme, which parameterises the droplet number concentration based on a change in supersaturation at a given time. Traditionally, aerosol activation parameterisation schemes were designed for convective clouds and assume that supersaturation is reached through adiabatic lifting, with many imposing a minimum vertical velocity (e.g. 0.1 m s−1) to account for the unresolved subgrid ascent. In radiation fog, the measured updraughts during initial formation are often insignificant, with radiative cooling being the dominant process leading to saturation. As a result, there is a risk that many aerosol activation schemes will overpredict the initial fog droplet number concentration, which in turn may result in the fog transitioning to an optically thick layer too rapidly. This paper presents a more physically based aerosol activation scheme that can account for a change in saturation due to non-adiabatic processes. Using an offline model, our results show that the equivalent cooling rate associated with the minimum updraught velocity threshold assumption can overpredict the droplet number by up to 70 % in comparison to a typical cooling rate found in fog formation. The new scheme has been implemented in the Met Office Natural Environment Research Council (NERC) Cloud (MONC) large eddy simulation (LES) model and tested using observations of a radiation fog case study based in Cardington, UK. The results in this work show that using a more physically based method of aerosol activation leads to the calculation of a more appropriate cloud droplet number. As a result, there is a slower transition to an optically thick (well-mixed) fog that is more in line with observations. The results shown in this paper demonstrate the importance of aerosol activation representation in fog modelling and the impact that the cloud droplet number has on processes linked to the formation and development of radiation fog. Unlike the previous parameterisation for aerosol activation, the revised scheme is suitable to simulate aerosol activation in both fog and convective cloud regimes.

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Size-Resolved Surface-Active Substances of Atmospheric Aerosol: Reconsideration of the Impact on Cloud Droplet Formation

Environmental Science & Technology ◽

10.1021/acs.est.8b02381 ◽

2018 ◽

Vol 52 (16) ◽

pp. 9179-9187 ◽

Cited By ~ 12

Author(s):

Ana Kroflič ◽

Sanja Frka ◽

Martin Simmel ◽

Heike Wex ◽

Irena Grgić

Keyword(s):

Atmospheric Aerosol ◽

Cloud Droplet ◽

Droplet Formation ◽

Surface Active ◽

The Impact ◽

Active Substances

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The Impact of Ambient Atmospheric Mineral-Dust Particles on the Calcification of Lungs

Minerals ◽

10.3390/min11020125 ◽

2021 ◽

Vol 11 (2) ◽

pp. 125

Author(s):

Mariola Jabłońska ◽

Janusz Janeczek ◽

Beata Smieja-Król

Keyword(s):

Mineral Dust ◽

Smoking Habit ◽

Lower Lobe ◽

Ambient Air ◽

Dust Particles ◽

Masking Effect ◽

Amorphous Calcium Carbonate ◽

Calcium Salts ◽

The Impact ◽

First Time

For the first time, it is shown that inhaled ambient air-dust particles settled in the human lower respiratory tract induce lung calcification. Chemical and mineral compositions of pulmonary calcium precipitates in the lung right lower-lobe (RLL) tissues of 12 individuals who lived in the Upper Silesia conurbation in Poland and who had died from causes not related to a lung disorder were determined by transmission and scanning electron microscopy. Whereas calcium salts in lungs are usually reported as phosphates, calcium salts precipitated in the studied RLL tissue were almost exclusively carbonates, specifically Mg-calcite and calcite. These constituted 37% of the 1652 mineral particles examined. Mg-calcite predominated in the submicrometer size range, with a MgCO3 content up to 50 mol %. Magnesium plays a significant role in lung mineralization, a fact so far overlooked. The calcium phosphate (hydroxyapatite) content in the studied RLL tissue was negligible. The predominance of carbonates is explained by the increased CO2 fugacity in the RLL. Carbonates enveloped inhaled mineral-dust particles, including uranium-bearing oxides, quartz, aluminosilicates, and metal sulfides. Three possible pathways for the carbonates precipitation on the dust particles are postulated: (1) precipitation of amorphous calcium carbonate (ACC), followed by its transformation to calcite; (2) precipitation of Mg-ACC, followed by its transformation to Mg-calcite; (3) precipitation of Mg-free ACC, causing a localized relative enrichment in Mg ions and subsequent heterogeneous nucleation and crystal growth of Mg-calcite. The actual number of inhaled dust particles may be significantly greater than was observed because of the masking effect of the carbonate coatings. There is no simple correlation between smoking habit and lung calcification.

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MBL drizzle properties and their impact on cloud property retrievals

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-4307-2015 ◽

2015 ◽

Vol 8 (4) ◽

pp. 4307-4323

Author(s):

P. Wu ◽

X. Dong ◽

B. Xi

Keyword(s):

Liquid Water ◽

Cloud Droplet ◽

Number Concentration ◽

Effective Radius ◽

Liquid Water Path ◽

Water Path ◽

Cloud Property ◽

Annual Means ◽

Mean Differences ◽

The Impact

Abstract. In this study, we retrieve and document drizzle properties, and investigate the impact of drizzle on cloud property retrievals from ground-based measurements at the ARM Azores site from June 2009 to December 2010. For the selected cloud and drizzle samples, the drizzle occurrence is 42.6% with a maximum of 55.8% in winter and a minimum of 35.6% in summer. The annual means of drizzle liquid water path LWPd, effective radius rd, and number concentration Nd for the rain (virga) samples are 5.48 (1.29) g m−2, 68.7 (39.5) μm, and 0.14 (0.38) cm−3. The seasonal mean LWPd values are less than 4% of the MWR-retrieved LWP values. The annual mean differences in cloud-droplet effective radius with and without drizzle are 0.12 and 0.38 μm, respectively, for the virga and rain samples. Therefore, we conclude that the impact of drizzle on cloud property retrievals is insignificant at the ARM Azores site.

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Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Entraining Parcel Simulations

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0078.1 ◽

2018 ◽

Vol 75 (10) ◽

pp. 3365-3379 ◽

Cited By ~ 13

Author(s):

Gustavo C. Abade ◽

Wojciech W. Grabowski ◽

Hanna Pawlowska

Keyword(s):

Droplet Size ◽

Turbulent Mixing ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Cloud Microphysics ◽

Droplet Growth ◽

Size Spectrum ◽

Entrainment Rate ◽

The Mean ◽

The Impact

This paper discusses the effects of cloud turbulence, turbulent entrainment, and entrained cloud condensation nuclei (CCN) activation on the evolution of the cloud droplet size spectrum. We simulate an ensemble of idealized turbulent cloud parcels that are subject to entrainment events modeled as a random process. Entrainment events, subsequent turbulent mixing inside the parcel, supersaturation fluctuations, and the resulting stochastic droplet activation and growth by condensation are simulated using a Monte Carlo scheme. Quantities characterizing the turbulence intensity, entrainment rate, CCN concentration, and the mean fraction of environmental air entrained in an event are all specified as independent external parameters. Cloud microphysics is described by applying Lagrangian particles, the so-called superdroplets. These are either unactivated CCN or cloud droplets that grow from activated CCN. The model accounts for the addition of environmental CCN into the cloud by entraining eddies at the cloud edge. Turbulent mixing of the entrained dry air with cloudy air is described using the classical linear relaxation to the mean model. We show that turbulence plays an important role in aiding entrained CCN to activate, and thus broadening the droplet size distribution. These findings are consistent with previous large-eddy simulations (LESs) that consider the impact of variable droplet growth histories on the droplet size spectra in small cumuli. The scheme developed in this work is ready to be used as a stochastic subgrid-scale scheme in LESs of natural clouds.

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