EQUILIBRIUM CLOUD DROPLET RADIUS AND COMPETITIVE GROWTH IN AIR PARCEL CONTAINING MULTI-SIZED CLOUD CONDENSATION NUCLEI

Abstract. Cloud-aerosol interaction is a key issue in the climate system, affecting the water cycle, the weather, and the total energy balance including the spatial and temporal distribution of latent heat release. Information on the vertical distribution of cloud droplet microphysics and thermodynamic phase as a function of temperature or height, can be correlated with details of the aerosol field to provide insight on how these particles are affecting cloud properties and their consequences to cloud lifetime, precipitation, water cycle, and general energy balance. Unfortunately, today's experimental methods still lack the observational tools that can characterize the true evolution of the cloud microphysical, spatial and temporal structure in the cloud droplet scale, and then link these characteristics to environmental factors and properties of the cloud condensation nuclei. Here we propose and demonstrate a new experimental approach (the cloud scanner instrument) that provides the microphysical information missed in current experiments and remote sensing options. Cloud scanner measurements can be performed from aircraft, ground, or satellite by scanning the side of the clouds from the base to the top, providing us with the unique opportunity of obtaining snapshots of the cloud droplet microphysical and thermodynamic states as a function of height and brightness temperature in clouds at several development stages. The brightness temperature profile of the cloud side can be directly associated with the thermodynamic phase of the droplets to provide information on the glaciation temperature as a function of different ambient conditions, aerosol concentration, and type. An aircraft prototype of the cloud scanner was built and flew in a field campaign in Brazil. The CLAIM-3D (3-Dimensional Cloud Aerosol Interaction Mission) satellite concept proposed here combines several techniques to simultaneously measure the vertical profile of cloud microphysics, thermodynamic phase, brightness temperature, and aerosol amount and type in the neighborhood of the clouds. The wide wavelength range, and the use of multi-angle polarization measurements proposed for this mission allow us to estimate the availability and characteristics of aerosol particles acting as cloud condensation nuclei, and their effects on the cloud microphysical structure. These results can provide unprecedented details on the response of cloud droplet microphysics to natural and anthropogenic aerosols in the size scale where the interaction really happens.

Download Full-text

Technical Note: Frenkel Halsey and Hill analysis of water on clay minerals: Toward closure between cloud condensation nuclei activity and water adsorption

10.5194/acp-2019-276 ◽

2019 ◽

Author(s):

Courtney D. Hatch ◽

Paul R. Tumminello ◽

Megan A. Cassingham ◽

Ann L. Greenaway ◽

Rebecca Meredith ◽

...

Keyword(s):

Water Adsorption ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Technical Note ◽

Condensation Nuclei ◽

Adsorption Parameters ◽

Climate Effect ◽

Montmorillonite Clays ◽

Activation Theory ◽

Cloud Droplet Number Concentration

Abstract. Insoluble atmospheric aerosol, such as mineral dust, has been identified as an important contributor to the cloud droplet number concentration and indirect climate effect. However, empirically-derived Frenkel-Halsey-Hill (FHH) water adsorption parameters remain the largest source of uncertainty in assessing the effect of insoluble aerosol on climate using the FHH activation theory (FHH-AT). Furthermore, previously reported FHH water adsorption parameters for illite and montmorillonite determined from water adsorption measurements below 100 % RH do not satisfactorily agree with values determined from FHH-AT analysis of experimental cloud condensation nuclei (CCN) measurements under supersaturated conditions. The work reported here uses previously reported experimental water adsorption measurements for illite and montmorillonite clays (Hatch et al., 2012; Hatch et al., 2014) to show that improved analysis methods that account for the surface microstructure are necessary to obtain better agreement of FHH parameters between water adsorption and experimental CCN-derived FHH parameters.

Download Full-text

Shipboard Measurements of Aerosol Properties in the Coupled Ocean-Atmosphere System of the Northwest Tropical Atlantic

10.5194/egusphere-egu2020-5901 ◽

2020 ◽

Author(s):

Tim Bates ◽

Patricia Quinn

Keyword(s):

Solar Radiation ◽

Marine Boundary Layer ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Lower Atmosphere ◽

Radiation Balance ◽

Tropical Atlantic ◽

Shallow Convection ◽

Condensation Nuclei ◽

Aerosol Properties

<p>The fair-weather cumulus clouds, that cover much of the low-latitude oceans, affect the radiation balance of the planet by reflecting incoming solar radiation and absorbing outgoing longwave radiation.&#160; These clouds also drive atmospheric circulation by mixing the lower atmosphere in a process called shallow convection.&#160; This mixing, in turn, affects sea surface temperature and salinity by moderating the air-sea exchange of energy and moisture.&#160; Marine boundary layer (MBL) atmospheric aerosols play a role in the processes described above by scattering and absorbing solar radiation and by serving as cloud condensation nuclei (CCN) thereby influencing cloud droplet concentrations and size; the extent, lifetime, and albedo of clouds; and the frequency and intensity of precipitation. Quantifying the role of aerosols over the Northwest Tropical Atlantic is critical to advance understanding of shallow convection and air-sea interactions.</p><p>MBL aerosol properties were measured aboard the RV Ronald H. Brown during the EUREC4A and ATOMIC field studies in January/February 2020.&#160; Aerosols encountered during the study include background sulfate/sea spray particles and African dust/biomass burning particles.&#160; Aerosol physical, chemical, optical and cloud condensation nuclei properties will be presented and their interaction with local and regional circulation.</p>

Download Full-text

The relative importance of non-sea-salt sulphate and sea-salt aerosol to the marine cloud condensation nuclei population: An improved multi-component aerosol-cloud droplet parametrization

Quarterly Journal of the Royal Meteorological Society ◽

10.1256/smsqj.55609 ◽

1999 ◽

Vol 125 (556) ◽

pp. 1295-1313 ◽

Cited By ~ 7

Author(s):

COLIN D ODOWD ◽

JASON A LOWE ◽

MICHAEL H SMITH ◽

ANDREW D KAYE

Keyword(s):

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Sea Salt ◽

Relative Importance ◽

Condensation Nuclei ◽

Sea Salt Aerosol ◽

Aerosol Cloud

Download Full-text

The analysis of size-segregated cloud condensation nuclei counter (CCNC) data and its implications for cloud droplet activation

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-10285-2013 ◽

2013 ◽

Vol 13 (20) ◽

pp. 10285-10301 ◽

Cited By ~ 45

Author(s):

M. Paramonov ◽

P. P. Aalto ◽

A. Asmi ◽

N. Prisle ◽

V.-M. Kerminen ◽

...

Keyword(s):

Cloud Condensation Nuclei ◽

Critical Diameter ◽

Cloud Droplet ◽

Condensation Nuclei ◽

Ambient Aerosol ◽

Cloud Processing ◽

Aerosol Mass ◽

Diurnal Patterns ◽

Hygroscopic Properties ◽

Boreal Environment

Abstract. Ambient aerosol, CCN (cloud condensation nuclei) and hygroscopic properties were measured with a size-segregated CCNC (cloud condensation nuclei counter) in a boreal environment of southern Finland at the SMEAR (Station for Measuring Ecosystem-Atmosphere Relations) II station. The instrumental setup operated at five levels of supersaturation S covering a range from 0.1–1% and measured particles with a size range of 20–300 nm; a total of 29 non-consecutive months of data are presented. The median critical diameter Dc ranged from 150 nm at S of 0.1% to 46 nm at S of 1.0%. The median aerosol hygroscopicity parameter κ ranged from 0.41 at S of 0.1% to 0.14 at S of 1.0%, indicating that ambient aerosol in Hyytiälä is less hygroscopic than the global continental or European continental averages. It is, however, more hygroscopic than the ambient aerosol in an Amazon rainforest, a European high Alpine site or a forested mountainous site. A fairly low hygroscopicity in Hyytiälä is likely a result of a large organic fraction present in the aerosol mass comparative to other locations within Europe. A considerable difference in particle hygroscopicity was found between particles smaller and larger than ~100 nm in diameter, possibly pointing out to the effect of cloud processing increasing κ of particles > 100 nm in diameter. The hygroscopicity of the smaller, ~50 nm particles did not change seasonally, whereas particles with a diameter of ~150 nm showed a decreased hygroscopicity in the summer, likely resulting from the increased VOC emissions of the surrounding boreal forest and secondary organic aerosol (SOA) formation. For the most part, no diurnal patterns of aerosol hygroscopic properties were found. Exceptions to this were the weak diurnal patterns of small, ~50 nm particles in the spring and summer, when a peak in hygroscopicity around noon was observed. No difference in CCN activation and hygroscopic properties was found on days with or without atmospheric new particle formation. During all seasons, except summer, a CCN-inactive fraction was found to be present, rendering the aerosol of 75–300 nm in diameter as internally mixed in the summer and not internally mixed for the rest of the year.

Download Full-text

Cloud droplet activity changes of soot aerosol upon smog chamber ageing

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-9831-2014 ◽

2014 ◽

Vol 14 (18) ◽

pp. 9831-9854 ◽

Cited By ~ 27

Author(s):

C. Wittbom ◽

A. C. Eriksson ◽

J. Rissler ◽

J. E. Carlsson ◽

P. Roldin ◽

...

Keyword(s):

Uv Radiation ◽

Organic Material ◽

Mass Fraction ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Particle Morphology ◽

Organic Aerosol ◽

Condensation Nuclei ◽

Soot Particles ◽

Kohler Theory

Abstract. Particles containing soot, or black carbon, are generally considered to contribute to global warming. However, large uncertainties remain in the net climate forcing resulting from anthropogenic emissions of black carbon (BC), to a large extent due to the fact that BC is co-emitted with gases and primary particles, both organic and inorganic, and subject to atmospheric ageing processes. In this study, diesel exhaust particles and particles from a flame soot generator spiked with light aromatic secondary organic aerosol (SOA) precursors were processed by UV radiation in a 6 m3 Teflon chamber in the presence of NOx. The time-dependent changes of the soot nanoparticle properties were characterised using a Cloud Condensation Nuclei Counter, an Aerosol Particle Mass Analyzer and a Soot Particle Aerosol Mass Spectrometer. The results show that freshly emitted soot particles do not activate into cloud droplets at supersaturations ≤2%, i.e. the BC core coated with primary organic aerosol (POA) from the exhaust is limited in hygroscopicity. Before the onset of UV radiation it is unlikely that any substantial SOA formation is taking place. An immediate change in cloud-activation properties occurs at the onset of UV exposure. This change in hygroscopicity is likely attributed to SOA formed from intermediate volatility organic compounds (IVOCs) in the diesel engine exhaust. The change of cloud condensation nuclei (CCN) properties at the onset of UV radiation implies that the lifetime of soot particles in the atmosphere is affected by the access to sunlight, which differs between latitudes. The ageing of soot particles progressively enhances their ability to act as cloud condensation nuclei, due to changes in: (I) organic fraction of the particle, (II) chemical properties of this fraction (e.g. primary or secondary organic aerosol), (III) particle size, and (IV) particle morphology. Applying κ-Köhler theory, using a κSOA value of 0.13 (derived from independent input parameters describing the organic material), showed good agreement with cloud droplet activation measurements for particles with a SOA mass fraction ≥0.12 (slightly aged particles). The activation properties are enhanced with only a slight increase in organic material coating the soot particles (SOA mass fraction < 0.12), however not as much as predicted by Köhler theory. The discrepancy between theory and experiments during the early stages of ageing might be due to solubility limitations, unevenly distributed organic material or hindering particle morphology. The change in properties of soot nanoparticles upon photochemical processing clearly increases their hygroscopicity, which affects their behaviour both in the atmosphere and in the human respiratory system.

Download Full-text

The challenge of simulating the sensitivity of the Amazonian clouds microstructure to cloud condensation nuclei number concentrations

10.5194/acp-2019-474 ◽

2019 ◽

Author(s):

Pascal Polonik ◽

Christoph Knote ◽

Tobias Zinner ◽

Florian Ewald ◽

Tobias Kölling ◽

...

Keyword(s):

Cloud Condensation Nuclei ◽

Regional Scale ◽

Cloud Droplet ◽

Number Concentration ◽

Effective Radius ◽

Cloud Base ◽

Condensation Nuclei ◽

Aerosol Cloud ◽

Microphysical Properties

Abstract. The realistic representation of cloud-aerosol interactions is of primary importance for accurate climate model projections. The investigation of these interactions in strongly contrasting clean and polluted atmospheric conditions in the Amazon area has been one of the motivations for several field observations, including the airborne Aerosol, Cloud, Precipitation, and Radiation Interactions and DynamIcs of CONvective cloud systems – Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON-CHUVA) campaign based in Manaus, Brazil in September 2014. In this work we combine in situ and remotely sensed aerosol, cloud, and atmospheric radiation data collected during ACRIDICON-CHUVA with regional, online-coupled chemistry-transport simulations to evaluate the model’s ability to represent the indirect effects of biomass burning aerosol on cloud microphysical properties (droplet number concentration and effective radius). We found agreement between modeled and observed median cloud droplet number concentrations (CDNC) for low values of CDNC, i.e., low levels of pollution. In general, a linear relationship between modeled and observed CDNC with a slope of two was found, which means a systematic underestimation of modeled CDNC as compared to measurements. Variability in cloud condensation nuclei (CCN) number concentrations and cloud droplet effective radii (reff) was also underestimated by the model. Modeled effective radius profiles began to saturate around 500 CCN per cm3 at cloud base, indicating an upper limit for the model sensitivity well below CCN concentrations reached during the burning season in the Amazon Basin. Regional background aerosol concentrations were sufficiently high such that the additional CCN emitted from local fires did not cause a notable change in modelled cloud microphysical properties. In addition, we evaluate a parameterization of CDNC at cloud base using more readily available cloud microphysical properties, aimed at in situ observations and satellite retrievals. Our study casts doubt on the validity of regional scale modeling studies of the cloud albedo effect in convective situations for polluted situations where the number concentration of CCN is greater than 500 cm−3.

Download Full-text