4) Ozone and Tropospheric Pollution

ozone formation and destruction

at what distance from the surface is the concentration of O3 the highest?

20km

when did the O3 protection start?

when atmos reached 20% O2, and multicell life started to occur

what is mechanism 1 of O3 destruction

O3 is destroyed by a catalytic chain reaction, where it is converted to O2 by a chain carrier, in an unpolluted atmosphere, catalyst does not get destroyed, requires oxygen

what is the reaction for mechanism 1 of O3 destruction?

X+O3 → XO+O3
XO+O → X +O2

what must ‘X’ have in mech 1?

a free radical

what is a common example of a free radical for mech 1? what is it produced by?

NO, N2O+O → 2NO

what is the reaction for mech 1 with NO?

NO+O3 → NO2+O2
NO2+O → NO +O2

what is mechanism 2 for O3 destruction?

in a non-polluted atmosphere, lower in the stratosphere, without O radicals, doesn’t require oxygen, catalyst gets consumed

what is the reaction for mech 2 of O3 desctruction? what is the overall reaction?

O+CH4 → OH+CH3
OH+O3 → HOO+O2
HOO+O3 → OH+2O2
2 O3 → 3 O2

which is more complex, the formation or destruction of O3? why?

destruction, if rate of destruction increases, there will be less O3, but O3 can never be fully decimated. concentration will rise until the rate of net destruction meets the rate of production

what happens if concentration of free radicals increases in atmos? with what mechanism?

the rate of O3 destruction will increase, mech 1

how are Cl and Br formed in the atmos?

decomposition of gases containing the halides

what is the reaction for catalyst mechanism of O3 destruction? what is the overall reaction

CH3Cl → Cl+Ch3
OH+CH3Cl → Cl+others
Cl+O3 → ClO+O2
ClO+O → Cl+O2
O3 + O → 2 O2

about how many molecules of O3 can 1 Cl radical destroy?

10k

how does Cl normally exist in the atmos?

inactive forms, ClONO2 and HCl

how do CFC’s affect radical destruction of O3?

CFCs have Cl, and they have the potential to destroy a large part of O3

briefly explain polar vortex

resulting from extremely cold winter, air pressure drops in lower strato, with earth’s rotation, the vortex and matter are isolated, creating polar strato clouds

what does PSC stand for? what are they made of?

polar stratosphere clouds, HCl and HNO3

how is ClONO2 important in polar vortex?

it can diffuse into the aqueous layers of crystal

explain polar vortex reactions briefly?

ClONO2+H2O → HOCl+HNO3
Cl- + HOCl → Cl2+OH-
Cl2 + light → 2 Cl-

what is the reaction for mechanism 2 of O3 desctruction IN ANTarctic, what is the overall reaction?

Cl+O3 → ClO+O2
2ClO →ClOOCl
ClOOCl+UV → ClOO+Cl
ClOO → O2+Cl
2ClO → 2 Cl + O2

what is special about ClOOCl?

it’s only stable at very low temps

what are sources of O3 in troposphere?

power plants, motor vehicles, grass/forest

what is photochemical smog?

undesirable concs of O3 where it shouldn’t be

what are common reactants to form O3?

NO, unburned hydrocarbons, light

what are sources of NO?

internal combustion engines, electric power plants

what are sources of unburned HCs?

two cycled engines, evaporation of fuels, volatile organic carbons (VOC)

what are conditions to form O3 in the tropo?

substantial traffic and dense population, ample sunlight, little movement of air

what is the reaction for O3 formation in tropo?

VOC+NO+O2. → O3+HNO3+organics

what are the rcts of the O3 formtn in tropo? where do they come from?

VOC and NO, directly from exhaust

what are the pdts of the O3 formtn in tropo? special info?

O3 and HNO3, there is certain chemistry that must occur before you get these

Explain the NO diagram thing

NO is converted to NO2 by O2 and HC, then converted into O by O2, then into O3
NO2 can either go to be O, or O2/HC, or be free radicals and then form HNO3 and organic nitrates

what was important about the smog cycles?

formation of each molecule of O3 requires an O atmo for NO2 dissociations