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ELLIOT ATLAS: Our interest in the ATTREX mission is to try to understand
the chemical composition of air in the region
where the Global Hawk flies
and this is the upper troposphere
and particularly, the tropical upper troposphere.
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So we look at we look at the composition of air
at different altitudes to understand what happens
to the chemical compounds in the air,
how they are degraded
and also how they are transported
from the upper troposphere
through a layer of the atmosphere called
the tropical tropopause layer,
and ultimately into the stratosphere,
where for some of the types of compounds that we look at
participate in chemical ozone destruction
in the stratosphere.
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We do this by taking air
and compressing it into air samples,
which we bring back to the laboratory
and analyze the trace gas composition
in the air that we've collected.
MARIA NAVARRO: And the way that we sample is by taking air
on the different layers of the atmosphere.
So when the instrument is ready to sample,
we flush our manifold
by opening the exhaust valves in intervals.
When we're ready to take the sample inside of the canister,
we send a command through our ground computer
to open the solenoid valve
So the air would go through the solenoid valve that is open
and draw air inside of the canister.
ELLIOT ATLAS: So during a flight, we will collect it
at various intervals through the flight,
a total of 90 canisters through the flight,
which is actually quite a lot for us to measure.
MARIA NAVARRO: We have 90 canisters because that was a way that
we needed to set it up inside of the Global Hawk
just for the space needs.
And these are custom-made canisters of 1.3 litres.
To get the air from the atmosphere,
we use this manifold that is connected
to an inlet outside of the aircraft.
This one is our inlet when we draw the air
and goes inside of the canisters.
And the canisters are inside of "Area 61" on the aircraft.
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ELLIOT ATLAS: Once the aircraft is on the ground,
we remove our canisters from the aircraft
and bring them to the laboratory.
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In the laboratory what we see behind us
is the analytical system that allows us to measure
the chemical composition of the air in the canisters.
Over here is, starting from one side to the next,
is the computer control
that operates the system and stores the data
that is generated by the analytical system.
Next, we have our reference gases,
which are of known chemical composition,
which we use to compare against our unknown samples
that are collected on the aircraft.
Samples from these gases are introduced into this system,
which separates very minor trace gases,
that we're interested in analyzing,
from the bulk of the air
which is nitrogen and oxygen.
That's removed and we collect
the trace gases that we want to analyze in this system.
Next, the mixture of gases which are collected on here
are transferred using heat to the gas chromatograph.
The gas chromatograph
separates this mixture of compounds
into individual components over time.
During the course of the analysis
these compounds are released from this mixture
and separated in time.
They go into different detectors.
One of the detectors is a mass spectrometer,
which is very specific for individual compounds
that we can detect and know specifically
what the compound is.
We also use two other detectors,
a flame ionization detector,
which is sensitive just for hydrocarbon type compounds.
Compounds such as ethane, propane...
Light hydrocarbons.
And also an electron capture detector,
which is sensitive to a range of compounds
that contain halogens,
which is one of the group of compounds
that we're interested in analyzing.
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We try to look at the amounts of chemicals in this region,
and by looking at at their distribution and amounts,
we can say something about how fast these
compounds are transported
from the lower atmosphere into the stratosphere.
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