Does lightning create ozone?

Mike2

I wonder if lightning in the upper atmosphere can create ozone? Anybody know what the chemical reaction would be?

Astronuc

See - http://geo.arc.nasa.gov/sgg/chatfiel...emFreeTrop.pdf

O + O₂ -> O₃ apparently

kaisxuans

lighting creating ozone? well, i never heared of it before. but firstly, how would you get lighting up into the upper ozone area?

Mike2

Well, I'm thinking if some very large magnetic field waves (possibly from the sun) passed through the atmosphere, then perhaps large currents would be induced, causing lots of lighting, etc. Then I remembered the ionizer/air-cleaner I once owned. It would "ionize" the air and make if smell fresh. I think I remember someone telling me that this was ozone I was breathing.

Has anyone studied whether this is an effect of the sprites that are seen above the clouds by astronaughts? If so, maybe we can "seed" the upper atmosphere to produce sprites like we do in the lower atmosphere to make it rain.

kaisxuans

well that could be a thought but i dont really think it is possible though. and i think you spelt your last word wrong...
well, but iff it is true, then you will have along way to go into this!

sneez

Astronuc already correctly identified main reaction of ozone creation. Notice that its dependent on O and O2 quantities, if there is no O there is no O3. O2 is photodissociated by UV rays in stratosphere and mesosphere. Chapman reactions explain ozone formation in stratosphere and are applied in explanation of secondary ozone maximum at nighttime around mesopause ~90km, eventhough the mesospheric chemistry can be quite involved and efficiently driven by atmospheric dynamics.

If there is any efficient way lightning could produce O3 it definitelly amounts to nothing in contribution to global ozone budget.

Second point is that breathing ozone is quite unhealthy:
EPA on ozone

mgb_phys

Lightning does create ozone but not in the ozone layer - that's much too high for there to be much lightning.
You create ozone in the lab in this way with an electrical spark.

The air ioniser you bought didn't create ozone, it merely ionises the air slightly and causes dust/pollen etc to become charged and stick to it. You can't actually smell it becoming cleaner and you can't smell ozone.
As sneez said, ozone is failry nasty stuff above 0.1ppm.

Mike2

OK, so what is the main mechanism for ozone production in the upper atmosphere? Thanks.

mgb_phys

UV radiation from the sun splitting oxygen molecules.
This also has the advantage of absorbing almost all of the uv < 400nm and stopping it reaching the surface, which means little pale skinned creatures are able to live there.

sneez

Let me build on what mgb explains already,

The ozone production is initiated by

1) O2 + hv -> O +O

2) O + O2 + M -> O3 + M ;The M stands for whatever 3rd reactant (N2 for example to carry out the energy from the reaction, without the M the reaction proceeds very slowly. Let me stress that this is the ONLY reaction by which ozone is created in the atmosphere.

3) O3 + hv -> O + O2

4) O + O3 -> O2 + O2

These are pure-oxygen photochemical steady state model of atmosphere, so called Champman's reactions. In stratosphere O3 has longer lifetime than O and hence the stratospheric ozone layer, which shows small diurnal variation due to imposibility of 1) and hence the destruction of O3 by 4) . (O concentrations bellow 40km are very small)

In upper atmosphere (mesosphere and lowe thermosphere (MLT)), O has long life time, at 80km as much as day and 100km as much as a week. Hence dynamics play very important role in this region. The concentration of O is larger than O3, hence at night O3 is created efficiently in MLT region, howerver, dynamics and catalytic cycles which destroy odd oxygen (O,O3) also start playing important role. Catalytic cycles by reaction of odd oxygen with H, OH, NO, Cl, Br for example.

Here we have an example of mean zonal distribution of O3 in stratosphere

Here altitude-latitude distribtuion, notice the upper atmospheric nighttime O3 concentration as well as the diurnally non-changing stratospheric O3 small figure

Mike2

Thanks. That was very informative. I wonder could the M also be H2O, water? I also wonder if there needs to be some input of energy UV or lightning to fascilitate this reaction in 2) above? I still wonder if sprites can create ozone. As I recall, they are lightning strikes going up (not down) from storm clouds. Thus, don't they thrust water up into the upper atmosphere and then send electricity through it to form ozone?

sneez

Review: the rate of raction of 2) R= k[O][O2][M] , k=rate constant (measured,sometimes infered form observations) , quantities in brackets have units of molecules/volume (number density)

I am sure that reaction constant for equation 2) is temperature dependent and 2) is exothermic, meaning it does proceed spontaneously no need for input of energy. Equation 2) becomes slower with increasing altitude (decreasing pressure/temp) and 3) (O3 + hv -> O2 + O2) becomes faster (more unattenuated sunlight at arond 320nm).

As far as M, lets think of it this way, 78% of atmosphere is N2, 20% O2, H2O and its typical mesospheric value of 4 ppmv or 4e-6 vmr = [H2O]/[air] , cannot play any significant role , however, M can be in theory any molecule, it does not change the speed of the reaction,ie. k in this case.

If sprites can create ozone which means increase density of O, since only reaction 2) creates ozone, it definitelly is not significant. As I said, O has increasing lifetime with increasing altitude and around 90-100km, has little diurnal variation.

H2O is photodissociated in upper atmosphere, H2O + hv -> H + OH, another interesting reaction is H + O3 -> OH + O2 and OH + O -> H + O2, these are responsible for the OH airglow layer in the nightime mesopause region.

As far as lightning in troposphere (of which I know more), its ionizes N2 and the later can create NO which in principle (if high enough concentration) can destroy ozone through
NO + O3 -> NO2 + O2

Given all the above, I am hesitating consider lightning to create ozone. The only way to do that is increase [O]. (Chemistry of atmospheres by Wayne, and Aeronomy of the middle atmosphere by Brasseur and Solomon do not mention lightning source of O3 as I checked the index)

Mike2

Wait, now I'm confused. I thought it was O3 that was protecting us from UV? But here you are saying that O2 in the upper atmosphere is absorbing UV. Is it both?

mgb_phys

Ozone does protect us from UV, the ozone molecule has lots of absorption in the 250-320nm UV-B band.
It seems I overstated the importance of the UV absorbed to manufacture the ozone.
Interestingly it appears that the ozone has another important effect, the UV absorbed by the ozone heats the layer to a higher temperature than it would otherwise reach. This high temperature upper layer stablilises the other layers of the atmosphere - stopping convection currents bringing very cold statospheric air down to sea level.

See, Wayne - Chemistry of atmospheres OUP 2000.

sneez

Well, in reality its both O2 and O3. O2 is responsible for extreme UV down to UV-C absorption, O3 sweeps out the remaining UV-C down to UV-A. They are very efficient, no photon makes it down at those wavelengths. (extreme UV dissociates N2 as well)

As mgb states, O + O2 + M -> O3 + M, is what determines the stratospheric temperature profile due to the M which carries out the energy of the reaction. A test question, why is the temperature maximum at around 50km while the ozone number density is around 25-35 km ?

Mike2

Could you tell me what the chemical reation is that causes the creation of ozone in the lab and how electricity is involved with it? Thanks.

mgb_phys

Basically the same as the UV except electrical energy rather than a photon.
Chemically I suppose you would write it as

O2 -> O + O
O2 + O -> O3