FC chemistry in the stratosphere Flashcards
(18 cards)
What percentage of O3 is found in the stratosphere
90%
Which species dominates stratosphere chemistry
O3 and O dominate stratospheric chemistry in the same way OH radicals dominate in the troposphere
Describe how O3 is produced in the stratosphere
O3 is produced photochemically, together with O in a cyclic process described by the chapman model
Compare and contrast chemistry in the stratosphere with chemistry in the troposphere
Species that survive physical losses and chemical conversions in the troposphere (N2O, CH4 and CH3Cl) are transported into the stratosphere where they yield the NOx, HOx and ClOx radicals that destroy O3.
Stratospheric chemistry is simple yet involves about 50 chemical species in nearly 200 reactions way more than the troposphere
What sort of substance is ozone
An endothermic substance
What type of reactions are those involving ozone
Reactions involving ozone are often exothermic and rates tend to be high, even more when it absorbs light.
Describe O3 formation in daylight hours
During daylight hours there is more photodisociation of O3 and O2 so there is more O2 and O species combining to make O3.
O3 has a very short photolysis lifetime during the day
Describe O3 formation at night
No photodissociation, so O and O(¹D) recombine or react, reducing odd oxygen concentrations. Reservoir species (NO₂, ClONO₂) become important in storing reactive species.
Describe the O3 chemistry at increasing altitudes
At increasing altitudes solar intensity is high but [O2] get low, therefore the formation of O3 gets slower but the [O]/[O3] gets higher
What is the main source of O species in the stratosphere
The source of the photolysis of O2 by short wavelength UV radiation
Describe the O3 chemistry at low altitudes
At low altitudes there is plenty of [O2] concentration but less radiation to dissociate it. Less UV radiation penetrates, leading to less ozone formation.
What is a null cycle
cycle which does nothing to the odd oxygen species, same number of odd oxygen on each side of the reaction
What is a holding cycle
holding cycle is a cycle which holds up species
What is a catalytic cycle
a cycle which leads to the destruction of odd oxygen
What wavelength of light photolyses O3
less than 310 nm
What wavelength of light photolyses o2
less than 240
What wavelength is UVB radiation
Radiation between 280 to 320
Why is photolysis of O2 not enough to protect life on earth from hazardous UV radiation from the sun
Photolysis of O2 (<240 nm) does not offer protection from the
hazardous UVB radiation (280 nm < λ < 320 nm). Photolysis of ozone
(<320 nm), on the contrary, can proceed in the UVB region, thus
shielding living organisms from harmful radiation
