1. OH Production in the Stratosphere and Troposphere The oxidizing capacity of t
ID: 107070 • Letter: 1
Question
1. OH Production in the Stratosphere and Troposphere The oxidizing capacity of the troposphere depends critically on the production of hydroxyl radicals (OH) by O3 photolysis. We learned that OH production occurs in the stratosphere, and the same process occurs in the troposphere. Here we evaluate the magnitude of the source in both regions, and the steady state concentration of OH in the troposphere. Rate Constant Stratosphere Troposphere R1. O3 hv O* O2 (si) 2x10-4 5x10-5 R2. O* M O M 3.8x10-11 11 k3 (cm3 molec-1 s-1) 2.2x10-10 R3. O* H20 2 OH a. Assuming O is in steady state in both the stratosphere or troposphere, calculate the production rate of OH in both regions using: strat 3000 ppb, trop 50 ppb, [O3] M]strat 18 molec cm 3, [M]trop 19 molec cm s, [H20]strat 2 ppm, LH20]trop 3x103 1%. See table for additional parameters.Explanation / Answer
a.The production of OH occurs in the third stage where conbination of O and H2O gives OH. In order to find the production rate of Oh in both regions,the calculations are as follows.
Production of OH in stratophere=1/[O3]strat*[H2O]strat/([M]strat*2.2×10^-10)
=(3×10^18*2.2×10^-10)/(3000*2)=110000molec cm-3/ppm
Production of OH in troposphere=([M]trop*2.2×10^-10)/([O3]trop*[H2O]trop)
=(2×10^19*2.2×10^-10)/(50*10,000) (1%=10000ppm)
=8800molec cm-3/ppm
b.The OH production in stratosphere=110000molec cm-3/ppm
The OH production in troposphere=8800molec cm-3/ppm
The lifetime of OH in stratosphere and troposphere=20 and 0.5s
OH number density in both the regions=(110000/20)+(8800/0.5)=23100molec cm-3/ppm
c.The production of OH varies in the two regionsions because the other components may contain different composition to produce OH and the stratosphere woukd receive more amount of OH when compared to troposphere as the layer is the top most layer.
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