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Chem 321 > Lecture 8 > Flashcards

Lecture 8 Flashcards

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1
Q

What is the stratosphere?

A

Between mesosphere and troposphere, is the the layer of atmosphere that protects life on earth

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2
Q

Whats the stratopause?

A

Boundary between stratosphere and mesosphere

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3
Q

What’s the tropopause?

A

Boundary between stratosphere and troposphere

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4
Q

What is the troposphere?

A

First region of atmosphere, keeps average temperature at 15 degrees

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5
Q

Why is water not included in the standard atmosphere?

A

Because it is highly variable

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6
Q

What is the distribution of water in the atmosphere?

A

A lot of water vapour in troposphere, less water vapour in stratosphere and tropopause

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7
Q

What is the distribution of ozone in the atmosphere?

A

Less than 1 but then increased in stratisphere and then decreases peak.

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8
Q

The sun emits black body radiation at what temperature?

A

T = 5770 K

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9
Q

What percent of radiation from the sun is visible?

A

43%

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10
Q

What is Weins displacement law?

A

A temp of object increases, the wavelength at which it emits most of it’s radiation becomes shorter.

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11
Q

What are the five types of major electromagnetic radiation?

A

X-rays, Ultraviolet, Visible, Infrared, microwave

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12
Q

What is the UV-C wavelength range?

A

200-280 nm

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13
Q

What is the UV-B wavelength range?

A

280-320 nm

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14
Q

What is the UV-A wavelength range?

A

320-400 nm

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15
Q

Where is absorption radiation highest of O2?

A

In the ionization continuum

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16
Q

Where is absorption radiation second highest of O2?

A

Schumann-Runge continuum

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17
Q

Where is absorption radiation third highest of O2?

A

Schumann-Runge bands

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18
Q

Where is absorption radiation the fourth highest of O2?

A

Herzberg continuum

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19
Q

Where is absorption of radiation highest in O3?

A

Hartley Band

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20
Q

Where is the absorption of radiation by oxygen and nitrogen highest? (include altitude and wavelength)

A

From 100-160 km, from 0-120 nm

21
Q

Where is the absorption of molecular oxygen?

A

30 km to 110 km, 120-220 nm

22
Q

Where does Ozone absorption begin?

A

0-40km, 220-300 nm

23
Q

Why is there little UV B or C at the surface of the atmosphere?

A

Because Ozone absorption of Uv-c in hartley band, uv-b gets partially asborbed towards the end of the hartley band

24
Q

What is the impact of UV radiation?

A

DNA mutations, skin cancer (melanoma), death
cataracts
crop failure

25
Q

When light intensity increases what happens to the relative biological sensitivity per photon?

A

It increases, with lower wavelengths (280 nm) holding the highest sensitivies.

26
Q

Does melanoma skin cancer increase with UV light intensity?

A

Yes

27
Q

How does the chapman mechanism work?

A

first step- High energy Uv-C photons with wavelengths smaller than 240 nm break O2 into two oxygen atoms.
second step- a free oxygen atoms reacts with a O2 molecule in the presence of a third molecule (N2 or O2), this results in an O3 molecule, heat, and molecule
third step- ozone absorbs UV-B and UV-C photons (wavelengths smaller than 330 nm), and splits it into oxygen and O2
fourth step- free oxygen atoms can react with ozone (O3), leading to it’s destruction and producing two oxygen molecules.

28
Q

The concentration of ozone in the stratosphere never exceeds what?

A

10 ppm

29
Q

The chapman mechanism absorbs what?

A

all remaining UV-C and much of UV-B

30
Q

The chapman mechanism creates what?

A

a steady state concentration of O3

31
Q

What is the minimum photon energy required to dissociate 1 molecule of O2?

A

498 kJ/mol

32
Q

What is a dobson unit?

A

is a measure of ozone abundance in the atmosphere, is equivalent to 2.69x10^16 molecules/cm^2. Is 0.01 mm of pure ozone at 273.15 K and 1 atm pressure

33
Q

What are the 3 main catalytic cycles that cause stratospheric ozone destruction?

A
  1. HO (hydroxyl)
  2. NO (nitric oxide)
  3. Reactive Halogens (Cl, Br)
34
Q

How does the hydroxyl reaction work?

A

hydroxyl reacts with O3 to produce HO2 and O2, HO2 and O (free oxygen) react to regenerate OH and produce O2 (molecular oxygen), the overall reaction is OH + O3 + HO2 +O -> Ho2 +O2 + OH + O2

35
Q

How does the nitric oxide reaction work?

A

NO + O₃ + NO₂ + O → NO₂ + O₂ + NO + O₂
NO react with ozone to create NO2 and O2 and No2 reacts with oxygen to create No and O2, removing ozone but recreating the radical

36
Q

How does the CL radical reaction work?

A

Cl+ O3 →ClO+ O2
ClO+ O → Cl + O2
Cl+ O3+ ClO+ O → ClO+ O2+ Cl+ O2

37
Q

What are chlorofluorocarbons?

A

compounds containing only C, F, and Cl
* nontoxic
* nonflammable
* volatile
* non-bioaccumulative
* inert
=> widely used since the 1940s in fridges and spray cans

38
Q

What researches found what about chlorofluorocarbons?

A

Identified CFCs are a source of reactive
chlorine in the stratosphere and predicted
catalytic ozone depletion

39
Q

What was the first observation of polar stratospheric ozone loss?

A

in the mis 1990s, ozone depletion occurred from the poles to australia and New Zealand in the south and Canada and russia in the north

40
Q

Much of the stratospheric chlorine is tied up in what?

A

reservoir species such as chlorine nitrate and hydrochloric acid

41
Q

What are reservoir species?

A

are species that are relatively long lived, they tie up large amounts of active (short-lived) species but can slowly re-release them.

42
Q

How is chlorine nitrate formed?

A

The combination of CLO and N2O, with sunlight

43
Q

How is HCL formed?

A

the Cl + CH4 react in an endothermic slow reaction to create the HCL and CH4

44
Q

How is chlorine formed?

A

The hydroxyl radical reacts with HCL, producing water, and regenerating the chlorine atom.
OH + HCl → H2O + Cl

45
Q

For chlorine, which species are active species that participate in chemical reactions such as ozone depletion?

A

active species are Cl and ClO since they are highly reactive free
radicals and participate in chemical reactions

46
Q

What is the impact of Polar stratospheric cloud on active chlorine (HCL & CLNO3)?

A

chlorine nitrate and HCL can react on the surface on PSCs to form CL2

47
Q

What was the Montreal protocol?

A

In 1987, Ban/phase-out of chlorofluorocarbons (CFCs) – used mainly as refrigerants and in
air conditioners
also gradual ban of HCFCs
some countries initially exempted (India, China)
Halons (contain Br; used in fire extinguishers) are also banned/phased-out
Regular “Ozone assessments”

48
Q

What were the results of the montreal protocol and follow up treaties?

A

CFC’s decreased in the northern hemisphere, CCL4 decreased

49
Q

The hole in earth’s ozone layer is the _______ since 1998

A

smallest it’s been

Chem 321 (6 decks)

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