Exercise 3 Activation of Cloud Droplets Background. In the lecture on cloud microphysics it has been shown that saturati

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Exercise 3 Activation Of Cloud Droplets Background In The Lecture On Cloud Microphysics It Has Been Shown That Saturati 1 (129.71 KiB) Viewed 144 times

Exercise 3 Activation of Cloud Droplets Background. In the lecture on cloud microphysics it has been shown that saturation ratio S for a droplet with radius r immersed in a non-volatile soluble hygroscopic aerosol can be written as a b S(r) = 1 + (10) r 739 where the value for the constant a can be found in the table en where the value of b is given by b= Ms 3imw Απρώης (11) where M, is the mass of the aerosol particle, m, is the molar mass of the aerosol, i is the degree of dissociation and ma is the molar mass of water and pw is the density of water. Assume that sea salt particles with a radius of 0.01 um act as cloud condensation nuclei (CCN). a. (10 points) Calculate the numerical value of b for these CCN. Make a plot of the Kohler curve for the saturation range S between 0.96 and 1.03. What is the size of the swollen sea salt particles at a saturation ratio of 0.98 (haze) ? b (10 points) Show that the critical radius, i.e. the radius beyond which the cloud droplet becomes activated is given by r* = (36)¹/2. (Tip: activation occurs at the maximum value of the Kohler curve. What is the value of the critical radius? At which saturation ratio does this occur? c. (10 points) Consider now that there are also larger salt particles with a size of 0.01 μm. As the environmental saturation S is increasing which droplets are activated first: the ones that grow on the small salt particles or the ones that grow on the larger salt particles. Explain your answer. variable description value Pw density of water mw molar mass water 10³ kg m-3 18 x 10-³kg 2.16 x 103 kg m-3 58.44 x 10-³kg PNaCl density of sea salt mNaCl molar mass sea salt constant in the curvature term for room temperature a 0.0011 μm. Table 1: Useful constants