Beloved Hydroxyl

I dedicated my Ph.D. thesis ‘to the hydroxyl radical, omnipresent but

ever elusive, you have a wicked sense of humour’.

In retrospect, this may seem a little theatrical. But at the time I truly felt

that I had been chasing this mysterious species for four years, day and night,

had sacrificed my life and happiness for it in fact, and to no joy. I thankfully

had a thoughtful supervisor and after four years of drowning in a mud pool and

banging my head on a brick wall he and my examining committee found it within

themselves to take pity on me, and allow me to submit a negative thesis. Two

hundred and forty-four pages on how not to measure hydroxyl radicals.

But I loved my project, I truly believed in it, I saw the potential it had

to physically expand our knowledge base and thereby our understanding of atmospheric

chemistry around the world. I did indeed dedicate my life at the time to this

doomed technique, and proving it would never work was sodden with mixed emotions.

I was glad that no-one would ever have to repeat all those terrible experiments

pointlessly, but I was also gutted.

Hydroxyl radicals are great, so informative about the immediate air composition,

and the method we were developing should have made them cheap and simple to

measure everywhere in the world.

Our method involved bubbling air through soluble aspirin and then analysing

the final solution. Hydroxyl radicals in the air react with aspirin to form

a product (2,5-dihydroxy benzoic acid if you must know) that is extremely fluorescent.

Separating reactants and products is relatively simple and the concentration

of the final product should be able to tell you how much hydroxyl is in the

air providing you know how long you bubbled for and what the flow rate was.

It really was that simple.

The two-hundred odd pages I mentioned above were dedicated to all the other

things that also react or interact with aspirin to produce the same result.

Light, ozone, bacteria, you name it. Even when we had got rid of most of them,

there was still an interference left and so, regrettably, we gave up. For what

we wanted to do, the method was rubbish.

Unfortunately for me, the best methods to measure atmospheric hydroxyl radicals

are still big and flash and expensive. They are actually wonderful instruments,

fascinating and amazing, but their cost necessarily means that there aren’t

many in the world.

Hydroxyl radicals, in contrast, are everywhere. Or a tleast they’re everywhere

that there’s any chemistry kicking off. They are present in tiny concentrations:

fractions of a part per trillion (that’s one hydroxyl in 10,000,000,000,000

anything elses) but they are crucial to keeping the chemistry happening. Where

there is pollution, they break it down and in so doing are themselves destroyed

and created. Where there is light, they are the mechanism that perpetuate photolytic

chain reactions. They are sometimes known as the dustbin of the atmosphere but

I prefer to think of them as little pac-men, munching their way through the

ever changing game. In fact, these are the same things that we are told we have

to control inside us by taking lots of antioxidants like tea, red wine and garlic.

Oxidising the air: good in general. Oxidizing your stomach: not so good. They

themselves aren’t good or bad, they’re molecules. They are however,

extremely powerful and effective. And better yet, a great indicator of everything

that’s going on around them.

Because of their low concentration and short lifetime (less than a second between

being produced and reacting with something else), they respond incredibly quickly

to changes in atmospheric composition. During the solar eclipse a few years

ago, for instance, the Leeds FAGE machine got some stunning data showing an

immediate drop-off of hydroxyl radicals when the sun disappeared and an immediate

return to their prior concentrations when the light returned. So they’re

good indicators of what’s going on in real time on a second-by-second

basis. Which is why I was so keen to develop a method that was cheap and cheerful,-

so we could get this data at every monitoring site from Halley to Weybourne.

Well, I may have not yet seen a global hydroxyl measurement network being

implemented for the cost of some pain-killers but I have seen hydroxyl measurements

in Antarctica. And that for me was pretty special. The ultimate combining of

two dreams I guess. To be honest, it was special for everyone concerned, and

not only for scientific reasons. First the ship didn’t get in so the project

was postponed by a year, then the ship did get in, the lab got built but we

didn’t think there would be enough energy for this beast to run in the

second summer when it was due to arrive. Then the beast got in, the power supply

was sufficient but the ice was weak and it looked like the beast may never get

out… from beginning to end, getting FAGE to the Antarctic was an investment

of nerves and faith as well as money.

There was an inherent risk even if the logistics would have run smoothly, too:

weather. As I said before, hydroxyl radicals are around in small concentrations

on the best of days. The best of days are sunny, clear, calm and long. On foggy,

windy, stormy, or icy days it was unlikely there would be enough radicals around

to measure them at all even if the machine stood up to the conditions. And we

didn’t know what kind of conditions it would withstand. I had been told

clearly at the start of last season that if we got two complete days of data,

that would be fine. If we got a week, that would be great.

As it turned out, the FAGE boys collected the longest data set from the instrument

ever, anywhere: 5 weeks of continuous measurements. And that in one of the most

remote and technically challenging places in the world. Everyone related with

the project should be rightfully proud.

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2 Responses to Beloved Hydroxyl

  1. Dwayne says:


    Best wishes,


  2. John says:

    Neat writing on OH. Very interesting to learn these things, especially with global warming.

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