All of the following raise the fraction of aerosol particles that activate in a cloud EXCEPT
Answer: A
A hydrophobic coating hinders wetting and raises the supersaturation required. The other three either supply more supersaturation or lower what each particle needs. Activation is always a contest between what is supplied and what is required.
Please log in or register to report this question.
Ageing of a soot particle in the atmosphere tends to
Answer: B
Correct answer: make it a more effective condensation nucleus over time
Fresh soot is hydrophobic and a poor nucleus. In the atmosphere it acquires coatings of sulphate, nitrate and organic material by condensation and coagulation, and those soluble coatings supply the solute term the Kohler curve needs. An aged soot particle therefore activates at a supersaturation that a fresh one would not, which is one reason the climate effect of a plume changes with distance from its source.
Please log in or register to report this question.
Consider the following statements about nuclei over land and sea.
1. Continental air generally carries more nuclei than maritime air.
2. Maritime clouds therefore tend to have larger droplets.
3. The nucleus concentration is much the same over land and sea.
Answer: C
The first two are correct and are among the best established contrasts in cloud microphysics. The third is contradicted by measurement, with continental values often ten times the maritime ones. The distinction is one of the oldest in observational cloud physics.
Please log in or register to report this question.
Three of the following describe the accumulation mode. Which is the odd one out?
Answer: D
Mechanically generated dust and sea salt belong to the coarse mode, which settles out comparatively quickly. The other three are the defining characteristics of the accumulation mode. Composition alone does not define a mode; the size range does.
Please log in or register to report this question.
Continental clouds may contain droplet concentrations of several hundred per cubic centimetre while maritime clouds hold about a hundred. For the same liquid water content this implies maritime droplets are
Answer: A
Correct answer: larger in radius by roughly a factor approaching two
For a fixed liquid water content the droplet volume goes inversely with the number, so the radius goes as the inverse cube root: a fivefold difference in concentration gives \( 5^{1/3} = 1.7 \) in radius. Maritime droplets are therefore appreciably larger, which is why marine clouds coalesce and rain more readily and why continental clouds - more numerous, smaller droplets - are brighter and longer lived. That is the indirect aerosol effect in one sentence.
Please log in or register to report this question.
