Cloud Condensation Nuclei Questions and Answers

Q: Consider the following statements about what makes a good condensation nucleus.1. Solubility lowers the critical supersaturation required.2. A larger dry radius also lowers that requirement.3. Only particles larger than ten micrometres can serve.

Correct answer: 1 and 2 onlyStatements 1 and 2 are correct and are the two terms of the Kohler curve: dissolved solute lowers the equilibrium vapour pressure and so the critical supersaturation, and a larger dry particle produces a larger droplet whose curvature penalty is smaller. Statement 3 is far too restrictive - effective nuclei are typically a tenth of a micrometre, and a ten micrometre particle would be a giant nucleus and vanishingly rare.

A cloud condensation nucleus is best defined as an aerosol particle that

A.activates into a cloud droplet at atmospheric supersaturations
B.nucleates the ice phase rather than the liquid phase
C.scatters sunlight strongly across the visible spectrum
D.remains suspended in the atmosphere for more than a year

Answer: A

Correct answer: activates into a cloud droplet at atmospheric supersaturations

The definition is functional rather than compositional: a particle counts as a condensation nucleus if it can be activated at the fraction of one per cent supersaturation a real cloud actually reaches. Ice nucleating particles are a separate and much rarer population, and scattering sunlight or persisting in the atmosphere are properties of aerosols generally rather than tests of nucleating ability.

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Consider the following statements about what makes a good condensation nucleus.
1. Solubility lowers the critical supersaturation required.
2. A larger dry radius also lowers that requirement.
3. Only particles larger than ten micrometres can serve.

A.All of them
B.1 and 2 only
C.3 only
D.1 only

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct and are the two terms of the Kohler curve: dissolved solute lowers the equilibrium vapour pressure and so the critical supersaturation, and a larger dry particle produces a larger droplet whose curvature penalty is smaller. Statement 3 is far too restrictive - effective nuclei are typically a tenth of a micrometre, and a ten micrometre particle would be a giant nucleus and vanishingly rare.

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Match each aerosol source with the kind of nucleus it supplies.
List I
A. Breaking waves
B. Fossil fuel combustion
C. Biomass burning
D. Marine biology
List II
1. organic and carbonaceous particles
2. sea salt particles over the ocean
3. sulphate from dimethyl sulphide
4. sulphate and soot particles

A.A-2, B-4, C-3, D-1
B.A-3, B-1, C-4, D-2
C.A-2, B-4, C-1, D-3
D.A-4, B-2, C-1, D-3

Answer: C

The mix determines both the number and the solubility of the available nuclei. Continental air typically carries an order of magnitude more of them than clean maritime air does. The contrast shapes droplet size and rainfall efficiency alike.

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Concentrations of cloud condensation nuclei in clean maritime air are typically of the order of

A.10000 per cubic centimetre
B.1 per cubic centimetre
C.1000000 per cubic centimetre
D.100 per cubic centimetre

Answer: D

Maritime values of roughly a hundred contrast with continental values of several hundred to a few thousand. Polluted continental air can exceed several thousand per cubic centimetre routinely. The range across the globe spans roughly two orders of magnitude.

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Assertion (A): Maritime clouds tend to contain fewer and larger droplets than continental clouds.
Reason (R): Clean maritime air supplies far fewer condensation nuclei for the same available vapour.

A.Both A and R are true, and R is the correct explanation of A
B.Both A and R are true, but R is not the correct explanation of A
C.A is true but R is false
D.A is false but R is true

Answer: A

Both are true and the reason gives the cause, and the same condensed water shared among fewer nuclei produces larger droplets. This is why maritime clouds precipitate more readily at a given depth. Larger droplets fall faster and sweep up their neighbours efficiently.

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For a fixed liquid water content, increasing the number of cloud condensation nuclei

A.removes the droplets from the cloud entirely
B.reduces the average size of the resulting droplets
C.increases the average size of the resulting droplets
D.leaves the average droplet size unchanged

Answer: B

The same mass of condensed water is divided among more droplets, so each is smaller. The consequences run through the whole life of the cloud, from its brightness to how readily it produces rain. Aerosol number is therefore a microphysical control on macroscopic behaviour.

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Assertion (A): A polluted cloud is brighter than a clean one holding the same amount of liquid water.
Reason (R): More and smaller droplets present a greater total surface area to scatter sunlight.

A.A is true but R is false
B.A is false but R is true
C.Both A and R are true, and R is the correct explanation of A
D.Both A and R are true, but R is not the correct explanation of A

Answer: C

Both are true and the reason gives the optics, and this brightening is known as the Twomey or first indirect effect. It represents a cooling influence that partly offsets greenhouse warming. Its magnitude remains among the least certain terms in the energy budget.

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The Twomey effect refers to

A.increased cloud lifetime from suppressed precipitation
B.the freezing of supercooled droplets on ice nuclei
C.the evaporation of cloud droplets by absorbing aerosol
D.increased cloud albedo from a greater number of nuclei

Answer: D

It is the first indirect aerosol effect and concerns brightness alone at fixed water content. The second option describes the lifetime or Albrecht effect, which is a separate and later idea. The two are frequently conflated but concern different cloud properties.

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Match each aerosol effect with what it describes.
List I
A. First indirect effect
B. Second indirect effect
C. Direct effect
D. Semi-direct effect
List II
1. aerosol scattering sunlight on its own
2. brighter cloud from smaller droplets
3. absorbing aerosol warming and evaporating cloud
4. longer lived cloud from less rain

A.A-2, B-4, C-1, D-3
B.A-4, B-2, C-1, D-3
C.A-2, B-4, C-3, D-1
D.A-3, B-1, C-4, D-2

Answer: A

The first two act through the cloud, while the direct effect needs no cloud at all. Distinguishing them matters because they differ in sign and in how confidently they can be quantified. Only the direct effect is straightforward to estimate from observation.

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10.

Assertion (A): Aerosol indirect effects are among the largest uncertainties in estimates of climate forcing.
Reason (R): They depend on cloud responses that vary greatly and are difficult to observe directly.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

Both are true and the reason gives the difficulty, and the response of cloud amount to aerosol is particularly hard to separate from meteorological variation. Successive assessments have narrowed the range only slowly.

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