Cloud Condensation Nuclei Questions and Answers

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.