METO 434
MIDTERM EXAM
50 points possible
October 12, 2000
Closed Book.
CIRCLE YOUR ANSWERS!!

NAME ______________________________________________

A. BASIC ATMOSPHERIC CHEMISTRY AND PHYSICS (20)

A1. (3) If this November a massive quantity of (1011 g) of the noxious fumigant "Elexsion" (CBr2ClF) is released and thoroughly mixed into the atmosphere, what will be its concentration in molecules cm-3, g/m3, and mixing ratio in ppt near the surface?  Assume RTP.

 

A2. (5) Estimate the concentration in the same three units for the approximate altitude of the top of the planetary boundary layer.

A3. (3) Sketch the altitudinal and latitudinal profiles of Elexsion mixing ratio if it has an atmospheric lifetime of four years. 

A4. (4) If the Henry's Law coefficient for Elexsion is 2 M/atm estimate the aqueous phase concentration in a cloud in the middle of the troposphere with LWC of 1.0g/m3.  Can wet deposition contribute substantially to the removal of this trace gas?  Explain. 

A5. (5)  Early efforts to control smog in Los Angeles by reducing sulfur emissions had little impact.  Explain why these measures failed and what pollutants and conditions actually cause Los Angeles-type smog.

B.  THERMODYNAMICS AND KINETICS (15)

B1. (4) The following reaction has been suggested as an important sink for methane, CH4.

Cl + CH4  HCl + CH3

In order to see if the suggestion reasonable calculate the room temperature:
Enthalpy, 
Gibbs Free Energy, and 
Equilibrium constant for this reaction. 

B2. (6) For this reaction, how many degrees of freedom does the reactive intermediate have?  
Do you expect this reaction to be fast or slow?  Explain.  
Estimate the rate constant for this reaction in appropriate units.  
Estimate the lifetime of Cl with respect to this reaction with CH4?

B3. (5)  For the following reaction

NO + O3  NO2 + O2

The forward rate constant is 2 x 10-14 cm3 s-1.  Estimate the reverse rate constant.

C. SPECTROSCOPY AND PHOTOCHEMISTRY (10)

C1. (3)  Find an expression for the steady state concentration of O3 in terms of  NO, NO2 and rate coefficients if the following reactions dominate.

NO2 + hv  NO + O		(1)

O + O2 + M  O3 + M	(2)

NO + O3  NO2 + O2		(3)

C2. (7) How does solar UV radiation intensity affect the steady state concentration of ozone?
What meteorological conditions favor the production of photochemical smog?

D. BIOGEOCHEMICAL CYCLES (5)

D1. (5)  Why do Earth's nearest neighbors in the solar system have atmospheres composed of CO2 rather than O2 and N2, and what impact does this have on their surface temperatures?

POTENTIALLY USEFUL INFORMATION

 Molecular Weights
 H = 1
 O = 16
 N = 14
 C = 12
 S = 32
 K = 39
 Br = 80
 Cl = 35.5
 F = 19

R = 2 cal/moleK = 8.31 J/moleK
N = 6.023x1023 molecules/mole
1 mole air = 22.4 L at STP
There are 1.8x1020 moles of air in the Earth's atmosphere.
The globally averaged OH number density is 9 x 105 cm-3 in the troposphere.
The current concentration of methane in the troposphere is 1750 ppb.

 Species	Hfo (kcal/mole)	  Gfo (kcal/mole)	
 H2O    	 57.8		 54.63	
 O3	 34.1	 39.0	
 NO	 21.6	 20.7	
 NO2	  8.1	 12.4	
 NO3     	-5.47 	 21.7	
 H2CO	-27.7	-26.3	
 HCO	  10.0	  8.0	
 HNO3     	-32.3	-17.9	
 Br	  26.7	 19.7	
 HBr	-8.66	-12.72	
 HCl    	-22.1	-22.8	
 CBr2ClF	-80	-85.	
 DMS	-20.	 -8.9	
 CH2-S-CH3	   8.0 	 10.0	
 CH4	-17.9	-12.1	
 CH3	  35.0	  30.0	
 Cl	  29.1	  25.3