U2 T4

Question 1

Since 1970s a reduction in atmospheric ozone has been observed in 2 different ways, which ones?

Answer 1

1. A general reduction –> 4% per decade over de hole planet

2. “Ozone holes” in polar regions where there is an annual drop stratospheric ozone concentrations

Question 2

Ozone concentration in Antarctica and Arctic have dropped up to…

Answer 2

Antarctica: dropped up to 2/3

Arctic : 1/3

Question 3

Why is there a concern about ozone depletion?

Answer 3

If UBV is not absorbed in the atmosphere then it h the Earth surface and may be absorbed by living cells.

Question 4

UV A (characteristics and wavelength)

Answer 4

• not absorbed by ozone

- 320-400nm

Question 5

UV B (characteristics and wavelength )

Answer 5

• almost fully absorbed by ozone

- 280-320 nm

Question 6

UV C

Answer 6

<280 nm Completely absorbed by ozone and normal oxygen

Question 7

The UV light considered in studying ozone depletion is :

Answer 7

UVB

Question 8

Which molecules absorbed UVB

Answer 8

UVB is absorbed by both diatomic and triatomic oxygen in photosynthesis reactions where the molecules are split.

Question 9

Why chlorine is very reactive ?

Answer 9

A single chlorine atom is a chlorine radical because it has an unpaired electron. This makes it very reactive

Question 10

O3

Answer 10

Ozone

Question 11

O2

Answer 11

Dioxigen (the one we breath)

Question 12

O

Answer 12

Monoatomic oxygen

Question 13

Cl

Answer 13

Chlorine

Question 14

ClO

Answer 14

Chlorine monoxide

Question 15

ClO2

Answer 15

Chlorine dioxide

Question 16

3 successional reaction between chlorine and ozone

Answer 16

1. a chlorine radical can react with an ozone molecule, breaking it down leave Ana oxygen molecule and chlorine monoxide.
2. The chlorine monoxide can then react with a monatomic oxygen atom to make chlorine dioxide
3. The ClO2 can then break down to release the chlorine again which may repeat these reactions thousands of times

Question 17

The important overall summary reaction

Answer 17

Cl + O3 + O—> 2O2 + Cl

Question 18

How does chlorine get to the stratosphere ?

Answer 18

Chlorine is very reactive so if it is released in the troposphere it will probably react with something else and never reach the stratosphere.

Question 19

What do CFCs contain?

Answer 19

Only chlorine, fluorine and carbon

Question 20

When were developed CFCs?

Answer 20

In the 1920s as the fluids of refrigerators and were later used as aerosol propellants, solvents and as the gases for expanded plastics such as expanded polystyrene

Question 21

What are the properties of CFCs that made them suitable for many use?

Answer 21

• they are chemically very stable
• Can be liquefied with pressure
• good solvents of grease and oils
• are not flammable
• most are not toxic

Question 22

HCFC that have replace CFCs in refrigerator also contain chlorine. Are they as dangerous as CFCs? Why?

Answer 22

HCFCs contain chlorine but they are less chemically stable so they break down before they reach the stratosphere and thus cannot damage the ozone layer

Question 23

Why is ozone depletion greatest in Polar Regions?

Answer 23

The chemical reactions involving chlorine and ozone require UVB but occur most easily at very los temperatures when ice crystals form that provide catalytic surfaces. During the Polar winter the temperatures drop and the allow the ice crystals to form, but there is no sunlight. When spring arrives, the crystals still exist and the sunlight causes the ozone- depleting reactions to take place.

Question 24

NOx

Answer 24

Oxides of nitrogen

Question 25

Do other gases cause ozone depletion ?

Answer 25

Oxides of nitrogen have been identified as possible causes of ozone depletion but releases in the troposphere do not reach the stratosphere as they dissolve in rain or react with other substances. High flying aircraft do release NOx into the stratosphere, but they are relatively very few so no obvious damage is caused