The hydroxyl radical. OH. is formed at low altitudes via

Chapter , Problem 83ie

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Problem 83ie

The hydroxyl radical. OH. is formed at low altitudes via the reaction of excited oxygen atoms with water:

O'(g) + H20(g)—2 OH(g)

(a)        Write the Lewis structure for the hydroxyl radical. (Hint: It has one unpaired electron.)

Once produced, the hydroxyl radical is very reactive. Explain the significance of each of the foDowing reactions or series of reactions with respect to pollution in the troposphere:

(b)        OH + N02—HN03

(c)        OH + CO + 02—«C02 + OOH OOH + NO-OH + N02

(d)        OH + CH4-H20 + CH3

CH3 + 02-00CH3

00CH3 + N0-0CH3 + N02

(e) The concentration of hydroxyl radicate in the troposphere is approximately 2 x 106 radicate per cm3. This estimate is based on a method called long path absorption spectroscopy (LPAS), similar in principle to the Beer's law measurement discussed in the Closer Look essay on p. 582. except that the length of the light path in the LPAS measurement is 20 km. Why must the path length be so large?

(f) The reactions shown in (d) also illustrate a second characteristic of the hydroxyl radical: its ability to cleanse the atmosphere of certain pollutants. Which of the reactions in (d) illustrate this?