Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
38 Cards in this Set
- Front
- Back
- 3rd side (hint)
|
The over prediction of [O3] from the chapman cycle can be partially explained by what?
|
Catalytic cycle involving OH and HO2 which can destroy ozone.
|
|
|
|
What are two main mechanism upon which OH is formed? Which is the main source of OH?
|
Main source for 90%) O(D1)+H2O->2OH or O(D1)+ CH4-> OH + CH3
|
|
|
|
Describe how HOx family may decrease the amount of ozone in the atmosphere.
|
Typically there are 3 paths to the HOx family: one will have a no net effect on O3, the other will contribute to one loss of O3 while the other contributes to 2 loss of O3. (SEE LECTURE 20 FOR MORE DETIALS)
|
|
|
|
What are the effects of [NO] and [NO2] on [O3] depletion
|
There are no direct effect of [No] and [NO2] on [O3].
|
|
|
|
How may you describe the effect of the HOx family on the Chapman cycle (explain the procedure)
|
Describe the rate of change of OH using the 4 HOx family reactions you assume the reaction is in equilibrium hence you may subtract it with the of the change for Ox (O3+O). Because NO2 reacts rapidly through photolysis, you may consider Steady state approximation and insert the expression in the overall expression.
|
|
|
|
On average how is the HOx reaction more efficient at destroying O3 compared to chapman mechanism?
|
HOx is 39% less effective than chapman.
|
|
|
|
Why is the HOx family mechanism alone problematic at explaining O3 depletion?
|
Based on themechanism, OH and HO2 would accumulate and O3 would eventually be entirelydepleted. |
Based on the mechanism, OH and HO2 would accumulate and O3 would eventually be entirely depleted.
|
|
|
HOx reactions accounts to a part of the over estimation of the Chapman cycle but it is not the entire story. What else also catalyse the [O3] destruction?
|
NOx family reactions.
|
|
|
|
What are the two NOx compounds and from what reaction does it come from?
|
NO2 and NO, they are produced by N2O
|
|
|
|
What happens to most of the N2O produced? What happens to it otherwise?
|
90% will undergo photolysis: N2 + O(D1) // N2O will react with O(D1); produce: 2 x NO or N2+O2
|
|
|
|
What is the main source of O(D1)?
|
Photodissociation of [O3]
|
|
|
|
What is the net reaction of the NOx cycle?
|
O3 + O-> O2+O2
|
|
|
|
What is the limiting step for the NOx cycle? How may you find it ?
|
The second step: use the life time theory.
|
|
|
|
What is peculiar about reaction 2 regarding the NOx cycle?
|
It competes with the photolysis of NO2 which eventually leads to O3 production. This hence means that if reaction 1 follows the competing reaction, you will have no net O3 loss. If reaction two occurs instead you will have O3 loss.
|
|
|
|
The NOx reaction compared to the HOx reaction is how many times more efficient at deteriorating [O3]? Where does this reaction occur and why?
|
4.5 times better. This occurs in the upper stratosphere where [O] is highest.
|
|
|
|
What would be the NOx cycle reaction on the lower stratosphere where [O] is almost absent?
|
NO can react directly with O3 NO2-> O3+ NO2-> NO3+hv->NO O2 hence you get rid of 2 x O3 in 3 x O2
|
|
|
|
Where do CFCs degrade typically?
|
In the stratosphere, UV light will degrade the CFC at 180 to 210 nm. The decomposition will typically produce chlorine radical.
|
|
|
|
What would be the two reactions in the chlorine cycle? Which reaction is the rate limiting step?
|
Cl+O3->ClO; ClO+O-> Cl+O2. The second reaction is much slower and hence is the rate limiting step.
|
|
|
|
What is the ClOx reaction cycle when reacting with NO? What is the net O3 loss?
|
Cl+O3->ClO(+NO)->NO2(+hv)->NO+O( Will not result in a net loss of O3 asO rapidly reforms O3) |
Cl+O3->ClO(+NO)->NO2(+hv)->NO+O ( Will not result in a net loss of O3 as O rapidly reforms O3)
|
|
|
How many times more efficient is the Chlorine cycle reaction O3 deterioration rate compared to Chapman Cycle?
|
1.1 times more.
|
|
|
|
On average, What is the ratio of Cl to ClO in the atmosphere?
|
0.008 which means that ClO is much more present in the atmosphere compared to Cl.
|
|
|
|
What happens to Cl at higher altitudes?
|
It guets sequestered away by CH4
|
|
|
|
What happens at ClO at lower altitudes?
|
NO2 reacts with it and creates ClONO2
|
|
|
|
What two compounds will store up to 99% of active Chlorine?
|
HCl and ClONO2
|
|
|
|
What will happen in the ClOx and NOx cycle when you have an increase in [OH]?
|
HCl will be converted back to Cl, but NOx will decrease in effectiveness.
|
|
|
|
What is the partial fraction of Cl in the stratosphere compared to bromide? How does this affect their effectiveness?
|
Cl 3400 ppt while Br is 20 ppt. They are both as important for O3 destruction.
|
|
|
|
Why the HOx NOx and ClOx cycles don’t entirely do destroys the ozone layer?
|
Because the reactive species the reactions create will react and become stable species without effect.
|
|
|
|
What happens when ClO and NO2 react? What happens to that product?
|
Forms ClONO2 which can be undergo photolysis to produce either the reactants or Cl & NO3
|
|
|
|
Why is Br so effective at destroying the ozone layer? ( compared to Cl)
|
Br will be produced rapidely and decompose slowly. This favors O3 decomposition as Br is in high concentration compared to Cl (only 1%).
|
|
|
|
What are the two main sources of ozone depletion?
|
CFCs and supersonic transport
|
|
|
|
What is so special about the Antartic to lead to ozone depletion?
|
During six months it becomes very cold in the Antartic. This create the polar vortex which prevents any warm air to come to the Antartic.. this lead to the polar stratospheric cloud. (where water condenses in the atmosphere when it shouldn’t. (lower the water lower the dew point)
|
|
|
|
How can you find the dew point of ice?
|
By ploting Pice-Ph2O with f(t). The x intercept will be the answer.
|
|
|
|
How can chlorine gas be produced through the aqueous layer of PSC?
|
ClONO2 goes in H2O to form HOCl(aq) but HCl can come and dissolve as well. Cl- reacts with HOCl to form Cl2 and OH-. Hence becomes the dominant form of chlorine gas.
|
|
|
|
Upon receiving photons in the polar vortex, What two reactions produces Cl-?
|
l2+hv->2Cl & HOCL+hv-> Cl- + OH-
|
|
|
|
Why does normal Cl mechanism wouldn’t work in the stratosphere for O3 destruction ? what happens instead?what wavelength of light is necessary for this to occur?
|
No [O] for the second reaction. Hence the other way is (ClO) 2x to regenerate Cl. This happens at a wavelength of 350 nm
|
|
|
|
Cl2O2 is very unstable normaly. Why is it stable in the polar vortex?
|
Because the temperature is extremely low which hence help stabilize its integrity.
|
|
|
|
What can also in Antartic regarding bromide and Chlorine ?
|
ClO and BrO react to gether to form Br and Cl which will react with O3 again
|
|
|
|
How can you have a global decline in ozone layer?
|
NO2 and No3 can react to do N2O5 which can be soluble in water to form HNO3 allowing for less ClONO2 and more ClO and Cl
|
|
