Lecture 8 Flashcards
What is the stratosphere?
Between mesosphere and troposphere, is the the layer of atmosphere that protects life on earth
Whats the stratopause?
Boundary between stratosphere and mesosphere
What’s the tropopause?
Boundary between stratosphere and troposphere
What is the troposphere?
First region of atmosphere, keeps average temperature at 15 degrees
Why is water not included in the standard atmosphere?
Because it is highly variable
What is the distribution of water in the atmosphere?
A lot of water vapour in troposphere, less water vapour in stratosphere and tropopause
What is the distribution of ozone in the atmosphere?
Less than 1 but then increased in stratisphere and then decreases peak.
The sun emits black body radiation at what temperature?
T = 5770 K
What percent of radiation from the sun is visible?
43%
What is Weins displacement law?
A temp of object increases, the wavelength at which it emits most of it’s radiation becomes shorter.
What are the five types of major electromagnetic radiation?
X-rays, Ultraviolet, Visible, Infrared, microwave
What is the UV-C wavelength range?
200-280 nm
What is the UV-B wavelength range?
280-320 nm
What is the UV-A wavelength range?
320-400 nm
Where is absorption radiation highest of O2?
In the ionization continuum
Where is absorption radiation second highest of O2?
Schumann-Runge continuum
Where is absorption radiation third highest of O2?
Schumann-Runge bands
Where is absorption radiation the fourth highest of O2?
Herzberg continuum
Where is absorption of radiation highest in O3?
Hartley Band
Where is the absorption of radiation by oxygen and nitrogen highest? (include altitude and wavelength)
From 100-160 km, from 0-120 nm
Where is the absorption of molecular oxygen?
30 km to 110 km, 120-220 nm
Where does Ozone absorption begin?
0-40km, 220-300 nm
Why is there little UV B or C at the surface of the atmosphere?
Because Ozone absorption of Uv-c in hartley band, uv-b gets partially asborbed towards the end of the hartley band
What is the impact of UV radiation?
DNA mutations, skin cancer (melanoma), death
cataracts
crop failure
When light intensity increases what happens to the relative biological sensitivity per photon?
It increases, with lower wavelengths (280 nm) holding the highest sensitivies.
Does melanoma skin cancer increase with UV light intensity?
Yes
How does the chapman mechanism work?
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.
The concentration of ozone in the stratosphere never exceeds what?
10 ppm
The chapman mechanism absorbs what?
all remaining UV-C and much of UV-B
The chapman mechanism creates what?
a steady state concentration of O3
What is the minimum photon energy required to dissociate 1 molecule of O2?
498 kJ/mol
What is a dobson unit?
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
What are the 3 main catalytic cycles that cause stratospheric ozone destruction?
- HO (hydroxyl)
- NO (nitric oxide)
- Reactive Halogens (Cl, Br)
How does the hydroxyl reaction work?
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
How does the nitric oxide reaction work?
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
How does the CL radical reaction work?
Cl+ O3 →ClO+ O2
ClO+ O → Cl + O2
Cl+ O3+ ClO+ O → ClO+ O2+ Cl+ O2
What are chlorofluorocarbons?
compounds containing only C, F, and Cl
* nontoxic
* nonflammable
* volatile
* non-bioaccumulative
* inert
=> widely used since the 1940s in fridges and spray cans
What researches found what about chlorofluorocarbons?
Identified CFCs are a source of reactive
chlorine in the stratosphere and predicted
catalytic ozone depletion
What was the first observation of polar stratospheric ozone loss?
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
Much of the stratospheric chlorine is tied up in what?
reservoir species such as chlorine nitrate and hydrochloric acid
What are reservoir species?
are species that are relatively long lived, they tie up large amounts of active (short-lived) species but can slowly re-release them.
How is chlorine nitrate formed?
The combination of CLO and N2O, with sunlight
How is HCL formed?
the Cl + CH4 react in an endothermic slow reaction to create the HCL and CH4
How is chlorine formed?
The hydroxyl radical reacts with HCL, producing water, and regenerating the chlorine atom.
OH + HCl → H2O + Cl
For chlorine, which species are active species that participate in chemical reactions such as ozone depletion?
active species are Cl and ClO since they are highly reactive free
radicals and participate in chemical reactions
What is the impact of Polar stratospheric cloud on active chlorine (HCL & CLNO3)?
chlorine nitrate and HCL can react on the surface on PSCs to form CL2
What was the Montreal protocol?
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”
What were the results of the montreal protocol and follow up treaties?
CFC’s decreased in the northern hemisphere, CCL4 decreased
The hole in earth’s ozone layer is the _______ since 1998
smallest it’s been
