Stratospheric Ozone Destruction

Question 1

Catalytic loss cycles for ozone destruction

Answer 1

O3 + X -> XO + O2
XO + O -> X + O2
OVERALL: O3 + O -> O2 + O2

X = HOx, NOx, HalOx

Question 2

What are reservoir species?

Answer 2

Metastable species that remove catalytic species, X, temporarily from the cycles. ** (which cycles)?

Question 3

What are examples of reservoir species?

Answer 3

HNO3, ClONO2

Question 4

Explain what is meant by a holding cycle

Answer 4

Formation and destruction of a catalytic species where the reversal process is known as photolysis/pyrolysis.

Example: NO3 + NO2 + M -> N2O5 + M

Question 5

Explain what is meant by a null cycle

Answer 5

A cycle where odd oxygen is not destroyed. (Clarify with friends)

Example: NO2 + O3 -> NO3 + O2
NO3 + hv -> O + NO2

If second equation was: NO3 + hv -> NO + NO2
Then odd oxygen would have been lost

Question 6

Halocarbon terminology

Answer 6

From Number to Formula:

1. Add 90 to the 2-digit/3-digit number (CFC-012)
2. Where for the produced 3-digit number:

d.e.f: d = no. of C, e = no. of H, f = no. of F
where no. of Cl = 2d + 2 - e - f

From Formula to Number:

Consider a 2 digit as 3 digit systems, therefore CFC-12 = CFC-012

a = no. of C -1
b = no. of H +1
c = no. of F

Question 7

Halon terminology

Answer 7

Halons: Fluorocarbons, no H involved, at least 1 Br atom attached

Each halon has an abcd format, where:
a - no. of C
b - no. of F
c - no. of Cl
d - no. of Br

Example: C2F4Br2 is Halon 2402

Question 8

Explain how the Antarctic ozone hole forms

Answer 8

Increase in CFC and halon concentrations (note that concentrations can predict amount of depletion but not when). The Antarctic has unique meteorology, where the polar vortex decouples southern polar air mass from the rest.

Question 9

Explain how low polar stratospheric clouds form

Answer 9

There are two types of polar stratospheric clouds:

Type I: Smaller than 1micro(mue symbol)meter diameter, where there are hydrates of HNO3 around a sulphate aerosol core.

Type II: These are larger than 1micrometer, and is essentially water ice on a type I PSC core. It forms when T drops below 195K, which is the frost point of water in the stratosphere.

Question 10

Explain what effects PSCs have

Answer 10

Type I clouds are known as sites of harmful destruction of the stratospheric ozone layer over the Antarctic and Artic. The surfaces of Type I clouds act as catalysts that turn man-made chlorine into active free radicals (ClO). In the return of the spring sunlight, the radicals destroy many ozone molecules, as seen in the chapman cycle.

Cloud formation is doubly harmful as it removes gaseous nitric acid from the stratosphere and combines with ClO to form less reactive forms of chlorine.