2.

Some diffusion problems in the atmosphere: [8 pts]

a.

A point source of 1000 g of SO₂ is released. If molecular diffusion (D = 0.12

cm²/s) takes place, (1) how long will it take to reach a standard deviation of

1 cm, 1 m and 100 m respectively, and (2) what are the maximum

concentrations at these times? [2 pts each]

b.

C.

By contrast, the molecular diffusion coefficient for a suspension of dust

(1μm diameter) in air (Brownian motion) is approximately D = 2.2 x 10°

cm²/s. Estimate the times now. Compare these to problem 2(a) and

comment on the behavior of smog (made up of SO₂ and dust particles and

other stuff!) in inversion layers over cites in which conditions are often

without turbulence. [3 pts]

An actual measurement during a SO₂ experimental point source release in

an inversion layer shows that the half width as measured by the 10% level

(i.e., where the concentration is 10% of the center point concentration) is

10 m at 1 hour after the release (see sketch). Estimate the diffusivity. Are

these molecular conditions (compare to 2(a))? [3 pts]

021

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Sxfel

10 m