Encounters with Strangers & Ideas & Personal & Science Posted by James Killus, 17 Oct 2007 05:59 am

Ozone in the Troposphere

…well yes you did get some kind of award for “Mostest Detailed Information on an Obscure Topic”. –JP Stormcrow

[D]on’t tempt me to go all photochemical on your ass. If you want detailed information on really obscure topics, I can bury you. –James Killus

Ozone is the key ingredient in photochemical smog. Air quality standards for smog are designed to limit ozone on the assumption that, if ozone is reduced, other photochemical smog constituents will also be reduced. While other air pollutants like carbon monoxide and fine particulates are, by and large, directly emitted, ozone is a “secondary air pollutant,” meaning that it is formed by chemical processes in the atmosphere.

There is, however, a natural background of ozone in the troposphere, the layer of air that contains 90% of the atmosphere, and the part of the atmosphere where we breathe, where weather happens, etc. Some of the tropospheric ozone is from the stratosphere; it slowly leaks down from above, through the tropopause, a very strong thermal inversion that exists, in fact, because the stratosphere contains so much ozone. Ozone absorbs infra-red radiation, so the stratosphere heats up and forms a thermal inversion “cap” that suppresses convective mixing. (The stratosphere is hot only in the relative sense. It’s still very cold; it’s just not as cold as the air immediately below it).

Most ozone in the stratosphere is formed by the direct photo-dissociation of oxygen by very short wave UV light, i.e., a different production pathway that can exist in the troposphere, because the stratosphere absorbs all the UV in those wavelengths before it reaches the troposphere. But near the bottom of the stratosphere, some of the ozone that is produced is formed by the “smog reactions,” from traces hydrocarbons (mostly methane) that manage to get through the tropopause, plus some nitrogen oxides that are formed from solar proton events, emitted from high altitude aircraft, and produced from the photolysis of nitric acid.

The smog reactions also work in the troposphere, of course, and not just in urban areas, although that’s where they are most obvious and where they were first studied. But there are natural sources of both reactive hydrocarbons (from trees, oil seepage, etc.) and nitrogen oxides (forest fires, lightning, bacterial action), and it’s pretty obvious (and inevitable) that some ozone will form that way.

So how much of the troposphere’s background of ozone begins in the stratosphere, and how much is formed in situ? There have been a lot of studies of this, from different directions. Leakage from the stratosphere, for example, can be estimated via tracers, including radioisotopes that were left over from nuclear bomb tests as they slowly leaked out of the stratosphere, and CFCs, as they slowly leaked into the stratosphere from below.

Estimating the strength of the tropospheric source is a little more difficult. I made a stab at it in the early 1980s, after an earlier stab at estimating the natural sources of nitrogen oxides.

The key to the analysis is a sort of “pseudo-stoichiometry” that exists in the smog reactions. Essentially, the process that forms ozone also destroys nitrogen oxides, although at a rate that depends on a lot of factors. One example of this destruction is in the case of the hydroxyl radical.

The hydroxyl radical (HO) is necessary for the oxidation of hydrocarbons that drives photo-oxidation, but HO also reacts with nitrogen dioxide, which is also necessary to form smog, to give nitric acid, the termination species (except in the stratosphere). This is only one of the radical species in the smog reactions that produces a sink for nitrogen oxides, so, as smog is formed, nitrogen dioxide is destroyed.

The ratio between ozone produced and nitrogen oxides being destroyed varies substantially, from less than 1 at high concentrations of precursors (such as in NOx rich plumes from power plants), to as high as 5 or even 10 to 1 at low concentrations under ideal conditions. I made various plausible estimates of the production ratios under various conditions for various NOx sources, and estimated the additional tropospheric ozone background that could be achieved from each source.

My estimates wound up being in the same ball park as prior estimates of the stratospheric ozone sources, around 1-4 ppb ozone, give or take. Given the uncertainties in just about every type of data going into the process, that was pretty good. It also had some bearing on a number of other questions, like the general photochemical background of “clean air,” and the fact that, over the past few decades, tropospheric ozone has been increasing. Since ozone is a (minor) greenhouse gas, the matter even has some application to climate change and global warming.

I presented these results in a poster session at a conference in the early 1980s, and one fellow who came by told my boss that he thought I was just the sort of smart fellow the field needed. That fellow was Paul Crutzen, who later got the Nobel Prize in Chemistry for his work on stratospheric ozone depletion. Having a future Noble laureate call me smart is one of those things that I don’t seem to be able to work into conversation nearly often enough.

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Responses to “Ozone in the Troposphere”

  1. on 17 Oct 2007 at 10:26 am 1. spyder said …

    Having a future Noble laureate call me smart is one of those things that I don’t seem to be able to work into conversation nearly often enough.

    Notably taken; however, your posts continuously exhibit your bright intellect on its own merits. Now the first question of the morning: given your research efforts and such, is there a shorter term solution to the depletion of the stratospheric ozone that seems to increase the penetration of UV into the troposphere, rather than the predicted long-term decay of ‘ozone-depletion’ gases over the next 150+ years??

  2. on 17 Oct 2007 at 11:37 am 2. James Killus said …

    The short answer is “no.”

    I’ve seen some cockamamie schemes to do things like burning up the CFCs with microwaves–that would have to be done before they got to the stratosphere, so then all that would remain would be the cleanout of the current stratospheric burden. I think I remember that has about a 50 year time frame.

    Then in my own hairbrained moments I think of things like putting something like baking soda up into the stratosphere to suck out all the current chlorine (during the time when it’s hydrogen chloride). The baking soda would fall out of the stratosphere in a year or two, so you’d be depleting the chlorine as it was generated. But the quantities involved would be vast, and almost certainly would create other problems that I haven’t thought of. At the very least it would be like a volcanic eruption, cutting down on sunlight and causing cooling, which would bring out the crazies saying that this was the solution to global warming, and the phrase “don’t go there” appears in my mind.

  3. on 17 Oct 2007 at 1:07 pm 3. Oaktown Girl said …

    Having a future Noble laureate call me smart is one of those things that I don’t seem to be able to work into conversation nearly often enough.

    I know just what you mean. Back when I was 12 years old, Ken Stabler called me “Sweetheart”.

  4. on 17 Oct 2007 at 1:40 pm 4. Kiera said …

    I know just what you mean. Back when I was 12 years old, Ken Stabler called me “Sweetheart”

    Little did he know…or even suspect. But still, he didn’t say you were a good football player, which would be more like the equivalent of James’ claim to fame.

  5. on 17 Oct 2007 at 1:44 pm 5. spyder said …

    Given your great post a few months back, in light of “this just in” from a half hour ago on the News Wires:

    Asked about Iran’s nuclear ambitions at his press conference today, President Bush warned for the first time in public of the risk of “World War III” if Iran gets nuclear weapons. “I’ve told people that if you’re interested in avoiding World War III,” said the President. “It seems like you ought to be interested in preventing them from have the knowledge necessary to make a nuclear weapon.”

    Now he seems to be saying that we no longer need to prevent Iran from having a nuclear weapon; we need to prevent Iran from having the knowledge necessary to make a nuclear weapon. The knowledge of course is something they already possess, as do many other countries (Pakistan for example); so is it possible we can read between the lies and discern the overt and more immediate US military action against Iran????

  6. on 17 Oct 2007 at 1:48 pm 6. Kiera said …

    I was going to say…anybody who is smart enough to use google on the internet has the knowledge to build a nuclear weapon (I guess that lets George out).

    How often must this man prove himself an idiot before the average American accepts it and rises up to protest our being represented at the highest levels by a fool (not to mention, outright liar)?

  7. on 17 Oct 2007 at 1:51 pm 7. Oaktown Girl said …

    But still, he didn’t say you were a good football player, which would be more like the equivalent of James’ claim to fame.

    It’s not about the equivalence factor, Li’l Miss Comment Buzz Kill! It’s about what it meant to me at the time, what it still means to me even now when I think back on it, and that I thought some would find the humor in it being compared to James’ Nobel Prize brush with greatness.

    Enjoy your stay in The Trunk. Lord Astaroth had one of his helper demons place a “silent but deadly” in there for your enjoyment.

  8. on 17 Oct 2007 at 2:06 pm 8. Kiera said …

    It was worth it, just for getting to imagine the expression on your face as you struggled not to explode at work. Oh yeah. Well worth it.

    Snicker

  9. on 17 Oct 2007 at 3:02 pm 9. Oaktown Girl said …

    Hey - no smart ass remarks from The Trunk section of the gallery.

  10. on 17 Oct 2007 at 3:10 pm 10. Kiera said …

    *smirks quietly*

  11. on 17 Oct 2007 at 7:47 pm 11. James Killus said …

    Well, there is this story, in which the second most impressive (i.e. ego stroking) thing in it is when one of my housemates came over to me and said, “Hey Jim, Ray Bradbury is on the phone and he wants to speak to you.”

  12. on 17 Oct 2007 at 7:53 pm 12. James Killus said …

    Oh, and Kiera, were you trying to imply that Ken Stabler wasn’t a good “Sweetheart” and his comment therefore meant little?

    [whistles softly as he walks away from the impending destruction].

  13. on 17 Oct 2007 at 8:02 pm 13. Kiera said …

    I don’t think either Oaktown Girl or I are gonna bite at that one, especially since you well know that Ken Stabler’s major claim to fame is as a football player, not as a sweetheart.

  14. on 17 Oct 2007 at 8:28 pm 14. Oaktown Girl said …

    Kiera - I think we both know what James meant to imply was that YOU were saying Ken Stabler wasn’t prestigious enough for me to be excited by him calling ME “sweetheart”. And yes, I am going to bite - retroactively. We’ll just add it to reasons why you had to go in The Trunk earlier today.

    [James walking away and whistling: you can just see the halo over his head not quite covering the horns. And then there’s that pointed red tail whipping around. Hmmm…oddly similar to a certain Minister of Justice we all know and love.]

  15. on 17 Oct 2007 at 9:15 pm 15. JP Stormcrow said …

    President Bush warned for the first time in public of the risk of “World War III” if Iran gets nuclear weapons.

    Check out this post of “A Map of the Apocalypse” at the always excellent Strange Maps blog. It is from the Jack Von Impe Ministries website where the question of the week consisted of this arresting dialogue.

    Are we headed for World War III?
    Alice Robinson
    Leesburg, NJ

    I believe we are in the final windup just before Christ returns to snatch us away in the twinkling of an eye before the world war begins. Now you say, why do you say that? Well, first of all Ezekiel 38 and 39 mentions Gog, Magog, Meshach, Tubal and Rosh as leading the war of the latter years and latter days. This didn’t happen a thousand years ago, it’s the final war, the latter years and latter days. All these cities are now in Russia and Putin has gone berserk and he is backing Iran and of course you know as I said already, last weeks program, the American Air Force is training the Saudi Arabians and the United Arab Emirates to combat them – that’s Russia and Iran and they’ll be on the side of the European Union and America and everything is coming to a head right now. I have never seen anything like it. For 50 years I’ve preached the coming war with Russia and now every single sign is in place. Yes, we’re headed for it.

    We are not worthy.

  16. on 18 Oct 2007 at 6:00 am 16. christian h. said …

    World War III - oh, the Hitchens’s of this world are going to be so happy. Finally, their chance! After the Iraq thing turned out to be a cakewalk-turned-quagmire, not at all a glorious sequence of tank battles in the desert, or bridges to be held by Jonah Goldberg until the cavalry arrives…

    Seriously, I think all these people just don’t manage to distinguish between real life and their Advanced Squad Leader game (irrelevant aside: anybody else ever play that? Most fiendlishly complicated boardgame I’ve ever seen…).