Two principle sources of CO to the atmosphere are oxidation of CH4 and combustion. Mean rate constants for oxidation of CH4 and CO by OH in the troposphere are k1= 2.5 * 10-15 and k2 = 1.5 * 10-13 cm3 molecules-1 s– , respectively. Observations indicate mean CO concentrations of 80 ppbv in the southern hemisphere, and a globally uniform CH4 concentration of 1700 ppbv. Calculate the fraction of CO source in each hemisphere contributed by oxidation of CH4. Comment on the interhemipheric difference.