I Have Officially Scared Myself

The folks at The World's Fair call it a meme, but it's really just a game:

...the premise is that you will attempt to find 5 statements, which if you were to type into google (preferably google.com, but we'll take the other country specific ones if need be), you'll find that you are returned with your blog as the number one hit.

This takes a bit of effort since finding these statements takes a little trial and error, but I'm going to guess that this meme might yield some interesting insight on the blog in question.

To make it easier, we'll let you use a search statement enclosed in quotations - this is just to increase your chances of turning up as number one, but if you happen to have a website with the awesome traffic to command the same statement without quotations, then flaunt it baby! Of course, once you find your 5 statements, pass the meme on to others.

Okay, this blog I have here is not a high traffic site; I'm pretty sure I have yet to hit triple digits for a single day. But...

Killus gives my sff.net web page. But the following single words bring you here:

• trademarksism
• semi-karma
• vertkrieg
• vuutle

But wait! There's more! The following search strings, sans quotes, also come up #1 on Google:

• brittle strategies
• John Galt is a slan
• fox hollow cafe lena
• nonrepresentational art pollack
• nonrepresentational art richard powers
• creepy little smile
• death rays and disintegrators
• playing the rent
• dead catfish under the drivers seat
• rocket boys meet radioactive boy scout
• max headroom stirner
• magic market fairy dust
• phony tough crazy brave alsop
• privation morality
• tihs not typo
• dorothy slave girl of oz
• knurdly lasers
• slan a critique

These need quotes:

• "black swan bashing"
• "son of on the road"
• "moral equivalent of socialism"
• "why barry goldwater lost tennessee"

I'm giving up now. And maybe going upstairs to pull the covers over my head.

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.

The Scientific Method

In my experience and observation, what’s sometimes taught in schools as “The Scientific Method” if fairly rare in the actual practice of science. But I’m going to brag a little about a time when I did get to go through the thing pretty much in the prescribed manner (from the Wikipedia entry on Scientific Method):

• Define the question
• Gather information and resources
• Form hypothesis
• Perform experiment and collect data
• Analyze data
• Interpret data and draw conclusions that serve as a starting point for new hypotheses
• Publish results
  

The question we were working on was the photooxidation of toluene (used as a solvent and a component of gasoline) in photochemical smog. It’s a moderately complicated molecule, a benzene ring with a methyl group replacing a hydrogen, and somewhere in its oxidation process, we knew that the ring had to open, and, well, then what?

What I brought to the problem was systems theory and a familiarity with simulation modeling, something that the previous generation of smog researchers had only intermittently. In articular, I was concentrating on the mass flows in the system, which you’d think that chemists would do as a matter of course, but no, they didn’t. In fact, in most generalized photochemical mechanisms that I analyzed, it turned out they didn’t conserve carbon. In once case the non-conservation was so bad that it actually was an infinite carbon generator; the mechanism alone generated more hydrocarbons than did emissions!

So anyway, I was looking to see how toluene oxidized in the atmosphere. Now smog is basically a “slow burn,” with the “burning” mediated by what are called free radicals, in this case hydroxyl (HO), and peroxyl, the simplest being hydroperoxyl (HOO). The HO and peroxyl radicals cycle back and forth in the oxidation process, and one of the byproducts is ozone.

The source of the radicals is partly burned hydrocarbons: aldehydes, ketone, glyoxals, a lot of things having a carbonyl group (C=O) in them. Some of these are emitted by automobiles directly, but the smog process makes during its slow burn. These compounds are photolytic; the break down in the presence of UV light to form free radicals.

The smog process also consumes the primary “fuels,” hydrocarbons and nitrogen oxides (NOx), with the burn essentially ceasing when the system runs out of NOx.

What I was looking at was the “stoichiometry” of ozone formed as a ratio to NOx consumed. It varies with conditions, so I put “stoichiometry” in quotes. While running my numbers for various hydrocarbons, it became pretty clear that toluene produced much less ozone per unit of NOx than did other hydrocarbons.

Whitten had already gotten an ad hoc simulation mechanism for toluene by reacting it with a short-lived species nitrogen trioxide (NO3). We figured that the NO3 was reacting with some oxidation product of toluene, which wasn’t a very big leap, partly because the “ring-opened” compounds would have a lot of very active double bonds (C=C) that were known to react with NO3.

I’ll also mention that my systems analysis strongly suggested that toluene was producing something that photolyzed very rapidly to free radicals. That meant that toluene, if added to other hydrocarbons, would accelerate the oxidation process. But the above-average consumption of NOx should then terminate the reaction at a lower level of ozone than would occur from the other hydrocarbons.

We had an EPA contract that let us suggest smog chamber experiments to the University of North Carolina researchers who had a two-sided, outdoor smog chamber that was perfect for controlled experiments. So I suggested that they load one side of the chamber with a standard mix of NOx and propylene (or propene, or methyl ethane, which are different words for the same stuff), and the other side with the same mix, plus some toluene. I told them that it should form ozone more quickly in the morning but produce an ozone peak that was notably less than
the control side.

It’s been called a “daring prediction.” I don’t remember feeling that daring. It seemed pretty inevitable to me, and I would have been mightily surprised if it hadn’t worked. I’ll never know, because it worked exactly as I predicted.

There were other hydrocarbons known to suppress ozone formation. Some like reactive olefins, simply react directly with ozone, so if there’s enough of them around, they’ll destroy the ozone as it’s being formed. One of them, isoprene, produces some very bizarre looking ozone curves in smog chamber experiments, where the ozone first goes up, then down, then up again after the isoprene has all been destroyed, but while the partly oxidized products of the isoprene still can
continue to react. Continuing my brag, I was the first person to get those double peaks in simulations also.

Another class of hydrocarbons suppressed ozone formation by soaking up free radicals. One is called DEHA (diethylhydroxyamine, if memory serves), and it was touted as a smog palliative for a while, until it was shown to boost smog once its radical absorption property was used up.

What we’d done, however, was to show that there was a new class of compounds that could, under some conditions reduce ozone peaks. It wasn’t anything like a smog palliative, because toluene is nasty stuff, and the things it forms are nastier still. But scientifically, it was very cool research.

Later we published a brief communication on the two-sided experiment alone, and also a paper on our toluene photooxidation mechanism. I don’t think that all the products of toluene oxidation have been identified to this very day, but we got the main features of its mass balance and ozone formation behavior twenty years ago. As they say, it was good enough for smog research.