Every few months, a team from
the Australian Government science agency, CSIRO,
and the Australian Bureau of Meteorology
will bottle up air from here, at the northern tip of Tasmania,
and send it off to be archived.
A few days ago, back on the Australian mainland,
in a suburb of Melbourne,
I interviewed one of the team at the Air Archive
to explain how and why.
- The first tank was taken on the 26th of April, 1978.
All up, we have close to 200 tanks spanning almost 50 years.
The pressure they get to is around-about 900 PSI.
They're 34 liter tanks, which means they hold
around 2,000 liters of air once they're completely full.
- This place, Kennaook / Cape Grim, has the cleanest air in the world...
when the wind's blowing from the south-west,
when that air has traveled thousands of kilometers
across the Southern Ocean without touching land.
So that is a monitoring station,
testing the levels of dozens of gases and chemicals in the atmosphere.
- When we say clean air or baseline air,
we mean that it has not had recent contact with land or pollution sources.
We know that it's very representative of the mid-latitudes
of the Southern Hemisphere background air.
Most of the sources of the major greenhouse gases
are in the northern hemisphere
because that's where the major population centers are.
It takes about a year to do the inter-hemispheric transport,
going across the equator is much, much slower than
the mixing within a hemisphere itself.
We wait until the wind is coming from the southwest direction,
and normally we wait several hours.
- Today, the wind is not blowing in the right direction!
It's blowing in from the cities in Tasmania and the Australian mainland,
but the team here are going to do a "practice fill"
of an archive cylinder, so they can show you what would happen.
And it's a really technical operation that has to avoid contamination.
- These cylinders are filled cryogenically, under vacuum.
When they're put into the liquid nitrogen,
the air naturally will be sucked into the tanks
over a two- to three-hour period.
- As any gas cools down, it compresses.
So initially the air rushes in to fill the vacuum,
but then it hits liquid nitrogen-chilled stainless steel,
so it cools and compresses and more air rushes in,
which cool and compresses, and so on, and so on and so on.
It's a really clever way to fill a pressurized canister without pumps.
- We then let it heat up or warm up,
and then we blast whatever water is in there out.
There is water in the tanks because there's water in the atmosphere,
and we don't do any drying.
We don't want to use pumps or any particular drying agent or method,
as this can potentially contaminate the tanks.
- So I had an obvious question: how do they know
that the air in the archive tanks doesn't change over time,
through some chemical reaction, or osmosis through a faulty valve,
or microbe contamination?
- We take measurements of the archive regularly,
maybe once a year we'll "take a sniff" out of
each of the cylinders, so to speak,
to ensure trace gases are not drifting or changing.
There is a little bit of moisture and water in there
and there have been concerns where the microbes might be
changing the composition for some trace gases.
But from what we've discovered so far,
that's not really the case.
- So they've got an archive. What do they do with it?
Well, let's say someone discovers that actually,
there's a greenhouse gas or some other contaminant
that we should have been testing for,
for the last 50 years or so.
The researchers can go to the archive,
pull samples from the tanks,
and use modern equipment to test old air.
Remember CFCs? They've been testing for those on site here for years,
but it turns out the replacements also cause problems.
- After the CFCs were the interim replacements, HCFCs,
and then the replacements for those, HFCs.
It's only recently we've had the technology
to be able to measure those,
to build up a history back in time to 1978.
That would not be possible without the archive.
Some of the measurements we do take just 20-30ml of air.
We can actually take measurements down to parts per trillion.
- There was one more thing that Paul showed me back at Melbourne.
The first tank taken here in 1978?
It's not the oldest one in the archive.
- Several years ago, we did a media story,
and we started to get inquiries from the public saying,
"we've got older air than you".
And it turns out there was a lot of people out there
with old scuba tanks sitting in their garages.
And most scuba divers kept a diary of when they dived,
when and where the tank was filled.
So people started to donate their scuba tanks.
So we now have air back to 1956.
For some trace gases that we're interested in,
are perfectly fine to take the measurements.
- All right, I am...
I'm standing somewhere windswept and talking about infrastructure.
It's like the fifth time!
I'm amazed the microphone held up. Thank you so much.
- No worries!