ATMOSPHERIC CHEMISTRY

METO/CHEM 637

Homework #3

Due October 11, 2007

 

1. (4) Ozone can be produced photochemically in the troposphere by the following reaction sequence.

OH + CO → H + CO2             (1)

H + O2 + M → HO2 + M        (2)

HO2 + NO → NO2 + OH        (3)

NO2 + hn → NO + O             (4)

O + O2 + M → O3 + M†          (5)

CO + 2 O2 → CO2 + O3         NET

Calculate the rate coefficient for Reaction 4, i.e. j(NO2) or j4, using the actinic flux, quantum yield and cross section information provided in Pitts & Pitts chapter 3.  Report what you assumed for altitude, surface albedo, and zenith angle. Sketch the action spectrum.

 

 

 

 

2. (3) Sulfur dioxide can be measured with a colorimetric method in which the concentration of SO2 is linearly proportional to the absorbance of an aqueous solution used to trap gaseous SO2 from the atmosphere. As a calibration, 100 u g of SO2 produced a solution with a transmittance of 45.5%. A solution through which 300 L of air at 30 oC had been bubbled has a transmittance of 56%. Calculate the concentration of SO2 in the air in ppm, and mg/m3 at 30 oC.

absorbance = - ln (I/I0)

transmittance = (I/I0) x 100%

 

 

3. (3) Express the steady state concentration of HO2 as an algebraic expression assuming the following reactions control the chemistry of unpolluted air. Your final expression should not contain concentrations of difficult-to-measure quantities H, O(1D), or OH.

 

O3 + hn → O2 + O(1D)                        (6)

O(1D) + H2O → 2OH                         (7)

OH + CO → H + CO2                                    (1)

H + O2 + M → HO2 + M                    (8)

HO2 + O3 → 2O2 + OH                      (9)

HO2 + HO2 → H2O2 + O2                   (10)

What does the above reaction scheme tell you about the effect of odd hydrogen on tropospheric ozone? Would you reach a different conclusion if you included the reaction scheme shown in Problem 1?