Reduced efficacy of marine cloud brightening geoengineering due to in-plume aerosol coagulation: parameterization and global implications

Abstract. The intentional enhancement of cloud albedo via controlled sea-spray injection from ships (Marine Cloud Brightening) has been proposed as a possible method to control anthropogenic global warming; however, there remains significant uncertainty in the efficacy of this method due to, amongst other factors, uncertainties in aerosol and cloud microphysics. A major assumption used in recent cloud- and climate-modeling studies is that all sea spray was emitted uniformly into some oceanic grid boxes, and thus these studies did not account for sub-grid aerosol coagulation within the sea-spray plumes. We explore the evolution of these sea-salt plumes using a multi-shelled Gaussian plume model with size-resolved aerosol coagulation. We determine how the final number of particles depends on meteorological conditions, including wind speed and boundary-layer stability, as well as the emission rate and size distribution of aerosol emitted. Under previously proposed injection rates and typical marine conditions, we find that the number of aerosol particles is reduced by over 50%, but this reduction varies from under 10% to over 90% depending on the conditions. We provide a computationally efficient parameterization for cloud-resolving and global-scale models to account for sub-grid scale coagulation, and we implement this parameterization in a global-scale aerosol-climate model. We find that accounting for this sub-grid scale coagulation reduces cloud droplet number concentrations by 46% over emission regions, and reduces the global mean radiative flux perturbation from −1.5 W m-2 to −0.8 W m-2.

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Reduced efficacy of marine cloud brightening geoengineering due to in-plume aerosol coagulation: parameterization and global implications

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-10385-2013 ◽

2013 ◽

Vol 13 (20) ◽

pp. 10385-10396 ◽

Cited By ~ 13

Author(s):

G. S. Stuart ◽

R. G. Stevens ◽

A.-I. Partanen ◽

A. K. L. Jenkins ◽

H. Korhonen ◽

...

Keyword(s):

Climate Model ◽

Climate Modeling ◽

Cloud Droplet ◽

Global Scale ◽

Cloud Microphysics ◽

Point Sources ◽

Sea Salt ◽

Sea Spray ◽

Subgrid Scale ◽

Computationally Efficient

Abstract. The intentional enhancement of cloud albedo via controlled sea-spray injection from ships (marine cloud brightening) has been proposed as a possible method to control anthropogenic global warming; however, there remains significant uncertainty in the efficacy of this method due to, amongst other factors, uncertainties in aerosol and cloud microphysics. A major assumption used in recent cloud- and climate-modeling studies is that all sea spray was emitted uniformly into some oceanic grid boxes, and thus these studies did not account for subgrid aerosol coagulation within the sea-spray plumes. We explore the evolution of these sea-salt plumes using a multi-shelled Gaussian plume model with size-resolved aerosol coagulation. We determine how the final number of particles depends on meteorological conditions, including wind speed and boundary-layer stability, as well as the emission rate and size distribution of aerosol emitted. Under previously proposed injection rates and typical marine conditions, we find that the number of aerosol particles is reduced by over 50%, but this reduction varies from under 10% to over 90% depending on the conditions. We provide a computationally efficient parameterization for cloud-resolving and global-scale models to account for subgrid-scale coagulation, and we implement this parameterization in a global-scale aerosol-climate model. While designed to address subgrid-scale coagulation of sea-salt particles, the parameterization is generally applicable for coagulation of subgrid-scale aerosol from point sources. We find that accounting for this subgrid-scale coagulation reduces cloud droplet number concentrations by 46% over emission regions, and reduces the global mean radiative flux perturbation from −1.5 W m−2 to −0.8 W m−2.

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The relationship between aerosol and cloud drop number concentrations in a global aerosol microphysics model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-3207-2009 ◽

2009 ◽

Vol 9 (1) ◽

pp. 3207-3241 ◽

Cited By ~ 1

Author(s):

K. J. Pringle ◽

K. S. Carslaw ◽

D. V. Spracklen ◽

G. M. Mann ◽

M. P. Chipperfield

Keyword(s):

Size Distribution ◽

Cloud Droplet ◽

Global Scale ◽

Rate Of Change ◽

The Arctic ◽

Aerosol Size Distribution ◽

Percentage Error ◽

Empirical Relationships ◽

Wide Range ◽

Global Mean

Abstract. Empirical relationships that link cloud droplet number (CDN) to aerosol number or mass are commonly used to calculate global fields of CDN for climate forcing assessments. In this work we use a sectional global model of sulfate and sea-salt aerosol coupled to a mechanistic aerosol activation scheme to explore the limitations of this approach. We find that a given aerosol number concentration produces a wide range of CDN concentrations due to variations in the shape of the aerosol size distribution. On a global scale, the dependence of CDN on the size distribution results in regional biases in predicted CDN (for a given aerosol number). Empirical relationships between aerosol number and CDN are often derived from regional data but applied to the entire globe. In an analogous process, we derive regional "correlation-relations" between aerosol number and CDN and apply these regional relations to calculations of CDN on the global scale. The global mean percentage error in CDN caused by using regionally derived CDN-aerosol relations is 20 to 26%, which is about half the global mean percentage change in CDN caused by doubling the updraft velocity. However, the error is as much as 25–75% in the Southern Ocean, the Arctic and regions of persistent stratocumulus when an aerosol-CDN correlation relation from the North Atlantic is used. These regions produce much higher CDN concentrations (for a given aerosol number) than predicted by the globally uniform empirical relations. CDN-aerosol number relations from different regions also show very different sensitivity to changing aerosol. The magnitude of the rate of change of CDN with particle number, a measure of the aerosol efficacy, varies by a factor 4. CDN in cloud processed regions of persistent stratocumulus is particularly sensitive to changing aerosol number. It is therefore likely that the indirect effect will be underestimated in these important regions.

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Cloud, Aerosol, and Boundary Layer Structure across the Northeast Pacific Stratocumulus–Cumulus Transition as Observed during CSET

Monthly Weather Review ◽

10.1175/mwr-d-18-0281.1 ◽

2019 ◽

Vol 147 (6) ◽

pp. 2083-2103 ◽

Cited By ~ 6

Author(s):

Christopher S. Bretherton ◽

Isabel L. McCoy ◽

Johannes Mohrmann ◽

Robert Wood ◽

Virendra Ghate ◽

...

Keyword(s):

Boundary Layer ◽

Climate Model ◽

Layer Structure ◽

Trace Gases ◽

Cloud Droplet ◽

Cloud Microphysics ◽

Aerosol Concentration ◽

Spatiotemporal Variability ◽

Layer Versus ◽

Wildfire Smoke

Abstract During the Cloud System Evolution in the Trades (CSET) field study, 14 research flights of the National Science Foundation G-V sampled the stratocumulus–cumulus transition between Northern California and Hawaii and its synoptic variability. The G-V made vertically resolved measurements of turbulence, cloud microphysics, aerosol characteristics, and trace gases. It also carried dropsondes and a vertically pointing W-band radar and lidar. This paper summarizes these observations with the goals of fostering novel comparisons with theory, models and reanalyses, and satellite-derived products. A longitude–height binning and compositing strategy mitigates limitations of sparse sampling and spatiotemporal variability. Typically, a 1-km-deep decoupled stratocumulus-capped boundary layer near California evolved into 2-km-deep precipitating cumulus clusters surrounded by patches of thin stratus that dissipated toward Hawaii. Low cloud cover was correlated with estimated inversion strength more than with cloud droplet number, even though the thickest clouds were generally precipitating and ultraclean layers indicative of aerosol–cloud–precipitation interaction were common west of 140°W. Accumulation-mode aerosol concentration correlated well with collocated cloud droplet number concentration and was typically largest near the surface. Aitken mode aerosol concentration was typically larger in the free troposphere. Wildfire smoke produced spikes of aerosol and trace gases on some flights. CSET data are compared with space–time collocated output from MERRA-2 reanalysis and from the CAM6 climate model run with winds and temperature nudged toward this reanalysis. The reanalysis compares better with the observed relative humidity than does nudged CAM6. Both vertically diffuse the stratocumulus cloud layer versus observations. MERRA-2 slightly underestimates in situ carbon monoxide measurements and underestimates ozone depletion within the boundary layer.

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Evaluation of the sectional aerosol microphysics module SALSA implementation in ECHAM5-HAM aerosol-climate model

Geoscientific Model Development Discussions ◽

10.5194/gmdd-4-3623-2011 ◽

2011 ◽

Vol 4 (4) ◽

pp. 3623-3690 ◽

Cited By ~ 6

Author(s):

T. Bergman ◽

V.-M. Kerminen ◽

H. Korhonen ◽

K. J. Lehtinen ◽

R. Makkonen ◽

...

Keyword(s):

Climate Model ◽

Global Scale ◽

Good Choice ◽

Sea Salt ◽

Aerosol Size Distribution ◽

Size Distributions ◽

Computationally Efficient ◽

Model Studies ◽

Aerosol Module ◽

Aerosol Properties

Abstract. We present the implementation and evaluation of a sectional aerosol microphysics model SALSA within the aerosol-climate model ECHAM5-HAM. This aerosol microphysics module has been designed to be flexible and computationally efficient so that it can be implemented in regional or global scale models. The computational efficiency has been achieved by keeping the number of variables needed to describe the size and composition distribution to the minimum. The aerosol size distribution is described using 20 size sections with 10 size sections in size space which cover diameters ranging from 3 nm to 10 μm divided to three subranges each having distinct optimised process and compound selection. The ability of the module to describe the global aerosol properties was evaluated by comparison against (1) measured continental and marine size distributions, (2) observed variability of continental modal number concentrations, (3) measured sulphate, organic carbon, black carbon and sea salt mass concentrations, (4) observations of AOD and other aerosol optical properties from satellites and AERONET network, (5) global aerosol budgets and concentrations from previous model studies, and (6) model results using M7 which is the default aerosol microphysics module in ECHAM5-HAM. The evaluation shows that the global aerosol properties can be reproduced reasonably well using the coarse resolution of 10 size sections in size space. The simulated global aerosol budgets are within the range of previous studies. Surface concentrations of sea salt, sulphate and carbonaceous species have an annual mean within a factor of five of the observations, while the simulated sea salt concentrations reproduce the observations less accurately and show high variability. Regionally, AOD is in relatively good agreement with the observations (within a factor of two). At mid-latitudes the observed AOD is captured well, while at high-latitudes as well as in some polluted and dust regions the modeled AOD is significantly lower than the observed. Regarding the most investigated aerosol properties, the performances of SALSA and the modal aerosol module M7 against observations are comparable. However, SALSA reproduces the observed number concentrations and the size distributions of CCN sized particles much more accurately than M7, and is therefore a good choice for aerosol-cloud interaction studies in global models. Our study also shows that when including activation type nucleation process in the boundary layer, the modeled concentrations of particles under 50 nm in diameter are reproduced much better compared to when only binary nucleation is assumed.

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Aerosol water parameterization: long-term evaluation and importance for climate studies

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-16747-2018 ◽

2018 ◽

Vol 18 (22) ◽

pp. 16747-16774 ◽

Cited By ~ 6

Author(s):

Swen Metzger ◽

Mohamed Abdelkader ◽

Benedikt Steil ◽

Klaus Klingmüller

Keyword(s):

Water Uptake ◽

Climate Model ◽

Climate Modeling ◽

Mixed Solution ◽

Hygroscopic Growth ◽

Computationally Efficient ◽

Aerosol Model ◽

Term Evaluation ◽

Climate Studies

Abstract. We scrutinize the importance of aerosol water for the aerosol optical depth (AOD) calculations using a long-term evaluation of the EQuilibrium Simplified Aerosol Model v4 for climate modeling. EQSAM4clim is based on a single solute coefficient approach that efficiently parameterizes hygroscopic growth, accounting for aerosol water uptake from the deliquescence relative humidity up to supersaturation. EQSAM4clim extends the single solute coefficient approach to treat water uptake of multicomponent mixtures. The gas–aerosol partitioning and the mixed-solution water uptake can be solved analytically, preventing the need for iterations, which is computationally efficient. EQSAM4clim has been implemented in the global chemistry climate model EMAC and compared to ISORROPIA II on climate timescales. Our global modeling results show that (I) our EMAC results of the AOD are comparable to modeling results that have been independently evaluated for the period 2000–2010, (II) the results of various aerosol properties of EQSAM4clim and ISORROPIA II are similar and in agreement with AERONET and EMEP observations for the period 2000–2013, and (III) the underlying assumptions on the aerosol water uptake limitations are important for derived AOD calculations. Sensitivity studies of different levels of chemical aging and associated water uptake show larger effects on AOD calculations for the year 2005 compared to the differences associated with the application of the two gas–liquid–solid partitioning schemes. Overall, our study demonstrates the importance of aerosol water for climate studies.

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The relationship between aerosol and cloud drop number concentrations in a global aerosol microphysics model

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-4131-2009 ◽

2009 ◽

Vol 9 (12) ◽

pp. 4131-4144 ◽

Cited By ~ 54

Author(s):

K. J. Pringle ◽

K. S. Carslaw ◽

D. V. Spracklen ◽

G. M. Mann ◽

M. P. Chipperfield

Keyword(s):

Size Distribution ◽

Cloud Droplet ◽

Global Scale ◽

Rate Of Change ◽

The Arctic ◽

Aerosol Size Distribution ◽

Percentage Error ◽

Empirical Relationships ◽

Wide Range ◽

Global Mean

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Global-scale combustion sources of organic aerosols: Sensitivity to formation and removal mechanisms

10.5194/acp-2017-6 ◽

2017 ◽

Cited By ~ 1

Author(s):

Alexandra P. Tsimpidi ◽

Vlassis A. Karydis ◽

Spyros N. Pandis ◽

Jos Lelieveld

Keyword(s):

Organic Compounds ◽

Climate Model ◽

Hybrid Approach ◽

Model Performance ◽

Organic Aerosols ◽

Global Scale ◽

Emission Rates ◽

Computationally Efficient ◽

Combustion Sources ◽

Scavenging Efficiency

Abstract. Organic compounds from combustion sources such as biomass burning and fossil fuel use are major contributors to the global atmospheric load of aerosols. We analyzed the sensitivity of model-predicted global-scale organic aerosols (OA) to parameters that control primary emissions, photochemical aging and the scavenging efficiency of organic vapors. We used a computationally efficient module for the description of OA composition and evolution in the atmosphere (ORACLE) of the global chemistry-climate model EMAC. A global dataset of aerosol mass spectrometer measurements was used to evaluate simulated primary (POA) and secondary OA (SOA) concentrations. Model results are sensitive to the emission rates of intermediate volatility organic compounds (IVOCs) and POA. Assuming enhanced reactivity of semi-volatile organic compounds (SVOCs) and IVOCs with OH substantially improved the model performance for SOA. Use of a hybrid approach for the parameterization of the aging of IVOCs had a small effect on predicted SOA levels. The model performance improved by assuming that freshly emitted organic compounds are relatively hydrophobic and become increasingly hygroscopic due to oxidation.

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Cloud microphysics and aerosol indirect effects in the global climate model ECHAM5-HAM

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-3425-2007 ◽

2007 ◽

Vol 7 (13) ◽

pp. 3425-3446 ◽

Cited By ~ 307

Author(s):

U. Lohmann ◽

P. Stier ◽

C. Hoose ◽

S. Ferrachat ◽

S. Kloster ◽

...

Keyword(s):

Indirect Effects ◽

Cloud Cover ◽

Emission Inventory ◽

Climate Model ◽

Global Climate Model ◽

Cloud Droplet ◽

Cloud Microphysics ◽

Anthropogenic Aerosol ◽

Aerosol Effect ◽

Aerosol Emission

Abstract. The double-moment cloud microphysics scheme from ECHAM4 that predicts both the mass mixing ratios and number concentrations of cloud droplets and ice crystals has been coupled to the size-resolved aerosol scheme ECHAM5-HAM. ECHAM5-HAM predicts the aerosol mass, number concentrations and mixing state. The simulated liquid, ice and total water content and the cloud droplet and ice crystal number concentrations as a function of temperature in stratiform mixed-phase clouds between 0 and −35° C agree much better with aircraft observations in the ECHAM5 simulations. ECHAM5 performs better because more realistic aerosol concentrations are available for cloud droplet nucleation and because the Bergeron-Findeisen process is parameterized as being more efficient. The total anthropogenic aerosol effect includes the direct, semi-direct and indirect effects and is defined as the difference in the top-of-the-atmosphere net radiation between present-day and pre-industrial times. It amounts to −1.9 W m−2 in ECHAM5, when a relative humidity dependent cloud cover scheme and aerosol emissions representative for the years 1750 and 2000 from the AeroCom emission inventory are used. The contribution of the cloud albedo effect amounts to −0.7 W m−2. The total anthropogenic aerosol effect is larger when either a statistical cloud cover scheme or a different aerosol emission inventory are employed because the cloud lifetime effect increases.

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Cloud microphysics and aerosol indirect effects in the global climate model ECHAM5-HAM

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-3719-2007 ◽

2007 ◽

Vol 7 (2) ◽

pp. 3719-3761 ◽

Cited By ~ 7

Author(s):

U. Lohmann ◽

P. Stier ◽

C. Hoose ◽

S. Ferrachat ◽

E. Roeckner ◽

...

Keyword(s):

Indirect Effects ◽

Cloud Cover ◽

Climate Model ◽

Global Climate Model ◽

Cloud Droplet ◽

Cloud Microphysics ◽

Anthropogenic Aerosol ◽

Mixing Ratios ◽

Aerosol Mass ◽

Aerosol Emission

Abstract. The double-moment cloud microphysics scheme from ECHAM4 has been coupled to the size-resolved aerosol scheme ECHAM5-HAM. ECHAM5-HAM predicts the aerosol mass and number concentrations and the aerosol mixing state. This results in a much better agreement with observed vertical profiles of the black carbon and aerosol mass mixing ratios than with the previous version ECHAM4, where only the different aerosol mass mixing ratios were predicted. Also, the simulated liquid, ice and total water content and the cloud droplet and ice crystal number concentrations as a function of temperature in stratiform mixed-phase clouds between 0 and –35°C agree much better with aircraft observations in the ECHAM5 simulations. ECHAM5 performs better because more realistic aerosol concentrations are available for cloud droplet nucleation and because the Bergeron-Findeisen process is parameterized as being more efficient. The total anthropogenic aerosol effect includes the direct, semi-direct and indirect effects and is defined as the difference in the top-of-the-atmosphere net radiation between present-day and pre-industrial times. It amounts to –1.8 W m−2 in ECHAM5, when a relative humidity dependent cloud cover scheme and present-day aerosol emissions representative for the year 2000 are used. It is larger when either a statistical cloud cover scheme or a different aerosol emission inventory are employed.

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Marine cloud brightening – as effective without clouds

10.5194/acp-2017-484 ◽

2017 ◽

Author(s):

Lars Ahlm ◽

Andy Jones ◽

Camilla W. Stjern ◽

Helene Muri ◽

Ben Kravitz ◽

...

Keyword(s):

Direct Effect ◽

Radiative Forcing ◽

Cloud Droplet ◽

Droplet Radius ◽

Sea Spray ◽

Climate Engineering ◽

Cloud Optical Depth ◽

Clear Sky ◽

Aerosol Direct Effect ◽

Global Mean

Abstract. Marine cloud brightening through sea spray injection has been proposed as a climate engineering method for avoiding the most severe consequences of global warming. A limitation of most of the previous modelling studies on marine cloud brightening is that they have either considered individual models, or only investigated the effects of a specific increase in the number of cloud droplets. Here we present results from coordinated simulations with three Earth system models (ESMs) participating in the Geoengineering Model Intercomparison Project (GeoMIP) G4sea-salt experiment. Injection rates of accumulation mode sea spray aerosol particles over ocean between 30° N and 30° S are set in each model to generate a global-mean effective radiative forcing (ERF) of −2.0 W m−2 at the top of atmosphere. We find that the injection increases the cloud droplet number concentration in lower layers, reduces the cloud-top effective droplet radius, and increases the cloud optical depth over the injection area. We also find, however, that the global-mean clear-sky ERF by the injected particles is as large as the corresponding total ERF in all three ESMs, indicating a large potential of the aerosol direct effect in regions of low cloudiness. The largest enhancement in ERF due to the presence of clouds occur as expected in the subtropical stratocumulus regions off the west coasts of the American and African continents. However, outside these regions, the ERF is in general equally large in cloudy and clear-sky conditions. These findings suggest a more important role of the aerosol direct effect in sea spray climate engineering than previously thought.

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