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.