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11 Nov 2019
11. 4 OH concentrations in the past There has been interest r using Greenland ice core measurements of methane (CH 4 ) and formaldehyde (CH 2 O) to derive OH concentrations n the past. 1. The maın sink for CH20 in the Arctic is photolysis, with a mean rate constant k 1x10s.Oxidation of CH4 is the only significant source of CH2O. Show that the steady-state concentration of CH20 is given by where k 2.010-. exp(-1700/T) cm molecule",-1 is the rate constant for oxidation of methane by OH. 2. The Table below shows the concentrations (ppby) of CH20 and CH4 n Greenland for three historical periods: present, pre-industrial (1600 A.D.) and last glaciation (18,000 B.C.) [CH 4] [CH2 O] T, K Present1700 0.10 260 Preindustrial 740 0.050 260 Glacial 410 0.010 250 2.1-Compute the OH concentration (molecules cmã) over Greenland for each period. 2.2. How do you interpret the difference in OH concentrations between pre-industrial times and today? 2.3. One possible explanation for the difference in OH concentrations between glacial and pre-industrial times is that stratospheric ozone concentrations were higher in glacial times. Why would that be? How would that affect OH concentrations?
11. 4 OH concentrations in the past There has been interest r using Greenland ice core measurements of methane (CH 4 ) and formaldehyde (CH 2 O) to derive OH concentrations n the past. 1. The maın sink for CH20 in the Arctic is photolysis, with a mean rate constant k 1x10s.Oxidation of CH4 is the only significant source of CH2O. Show that the steady-state concentration of CH20 is given by where k 2.010-. exp(-1700/T) cm molecule",-1 is the rate constant for oxidation of methane by OH. 2. The Table below shows the concentrations (ppby) of CH20 and CH4 n Greenland for three historical periods: present, pre-industrial (1600 A.D.) and last glaciation (18,000 B.C.) [CH 4] [CH2 O] T, K Present1700 0.10 260 Preindustrial 740 0.050 260 Glacial 410 0.010 250 2.1-Compute the OH concentration (molecules cmã) over Greenland for each period. 2.2. How do you interpret the difference in OH concentrations between pre-industrial times and today? 2.3. One possible explanation for the difference in OH concentrations between glacial and pre-industrial times is that stratospheric ozone concentrations were higher in glacial times. Why would that be? How would that affect OH concentrations?