the atmospheric chemistry experiment (ace)
TRANSCRIPT
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The Atmospheric Chemistry
Experiment (ACE)
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ACE Primary Science GoalTo investigate the chemical and dynamical
processes that control the distribution of ozone inthe stratosphere and upper troposphere with a
particular focus on the Arctic winter stratosphere.
To accomplish this,
Temperature and pressure will be measured.
ACE will measure the concentrations of more than
30 molecules as a function of altitude.
Aerosols will be measured and quantified.
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Atmospheric Structure
O2 + h 2O*
2O* + 2O2 2O3*
UV photon
Excess energy goes
into thermal motion
of molecules.
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Volume Mixing Ratio
Ratio of gas partial pressure to total pressure.
Variation with altitude gives information on
chemical or photochemical processes
Ozone Vmr Profile
0
20
40
60
80
100
120
0 2 4 6 8 10
vmr (parts per million by volume)
Altitude(km)
CO2 Vmr Profile
0
20
40
60
80
100
120
100 150 200 250 300 350 400
vmr (parts per million by volume)
Altitude(km
)
CO Vmr Profile
0
20
40
60
80
100
120
0 50 100 150 200
vmr (parts per million by volume)
Altitude(km)
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Chlorofluorocarbons (CFCs)
Cl + O3 ClO + O2
ClO + O Cl + O2
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Stratospheric Chlorine The long lifetimes of CFCs led to increasing
Cl into the stratosphere (a very bad thing).
Eventually the Cl gets taken up in reservoir
molecules such as HCl and ClONO2.e.g., ClO + NO2 + M ClONO2 + M
However, atomic Cl can be released in large
quantities as a result of processes that occur
during polar winter, leading to ozone losses.
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Ozone Hole (continued) Temperature inside the polar vortex gets
very cold. For temperatures below -80 C,clouds composed primarily of HNO3 (polar
stratospheric clouds or PSCs) form.
Reactions that occur slowly (or not at all) in
gas phase readily proceed on the surface of
PSC particles (heterogeneous reactions).e.g., HCl + ClONO2 HNO3 + Cl2
HNO3 remains in cloud particle, while Cl2 is
released into the stratosphere.
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Ozone Hole (continued) No sunlight reaches the South Polar
stratosphere during the winter.
When sunlight returns in the spring, Cl2 is
photolysed into Cl atoms. Rampant ozone destruction ensues.
HNO3 tied up in PSC particles. Low
nitrogen and hydrogen levels slows thecreation of chlorine reservoir molecules,
exacerbating the destruction.
Recovery after polar vortex breakdown.
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Antarctic Ozone
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Fixing the Problem Montreal Protocol signed in 1987 to phase out
the use of CFCs.
CFC replacements hydrofluorocarbons (HFCs)
and hydrochlorofluorocarbons (HCFCs). HFCs contain no chlorine.
HCFCs are much more reactive than CFCs.
They undergo reactions in the troposphere thatcan remove them (e.g., conversion to water
soluble species that get rained out).
Less Cl transported to the stratosphere.
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HCl and ClONO2 Trends
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Role of ACE Investigate PSCs, particularly composition.
Monitor stratospheric chlorine levels.
Monitor CFCs and CFC replacements.
Monitor molecules associated with polarspring chemistry (e.g., ClO and ClONO2),
particularly at altitudes where PSCs are
present.
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Arctic Ozone No ozone hole occurs in the Arctic.
Arctic winter temperatures are not as cold
as for Antarctic winter. The polar vortex is
also less stable in the Arctic. However, sharp declines in ozone levels
are often observed during March/April
(spring in the Northern Hemisphere). The reasons for the declines are similar to
the cause of the Antarctic ozone hole
(chlorine activation via PSCs).
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Polar Spring Ozone
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Mid-Latitude Ozone Decline
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Mid-Latitudes Declines at mid-latitudes arise from a variety
of sources: CFCs, mixing of ozone-depletedair from polar spring events, heterogeneous
reactions on aerosol particles.
The extent of the losses cannot be explained
by current models.
Most recent mid-latitude measurementsindicate that the losses have leveled off, likely
related to the peaking of chlorine levels.
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Chemistry-Climate Coupling A model predicts there may be an Arctic
ozone hole in the 2010-2020 timeframe.
Chlorine levels are decreasing, but
greenhouse gas (e.g., CO2, CH4, N2O)levels are increasing.
Greenhouse gases warm the surface but
lead to a cooling of the stratosphere. A colder Arctic polar winter stratosphere
would lead to a more stable polar vortex
and more PSCs more ozone loss.
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Arctic Ozone Predictions
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Data Assimilation More reliable model predictions are needed
for the future of Arctic ozone. Long leadtimes would be required to implement policy
changes for greenhouse gas reductions.
ACE measurements (and other satellite
mission measurements and airplane- and
balloon- and ground-based data) needs tobe assimilated into models to improve the
reliability of the predictions.
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ACE Satellite
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Instruments Infrared Fourier Transform Spectrometer
operating between 750 and 4100 cm-1
witha resolution of 0.02 cm-1.
2-channel visible/near infrared Imagers,
operating at 0.525 and 1.02 microns Suntracker keeps the instruments pointed
at the suns radiometric center.
UV / Visible spectrometer (MAESTRO)
0.285 to 1.03 microns, resolution ~1-2 nm
Startracker
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ACE Payload
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ACE-FTS
MAESTRO (Fli ht M d l)
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MAESTRO (Flight Model)
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Optical Layout (Bomem)
Seconday
mirror (6)
Field stop (5)
IR Filter
(7)
Suntrackermirror (1)
Aperture
stop (4)
PV MCT
Detector
(18)
Glare stop(16)
Coolerwindow (17)
Output
condenser
(14)
INTcorner-cube
mirror (10)
End mirror
(13)
INT
corner-cubemirror (11)
(12)
(9)
(12): Reflective coating
(9): B/S coating
Beamsplitter/
compensatorassembly (8)
Primary mirror (3)
Fold mirror
(22)
Lenses
(23)
0.525 m
imager (28)
1.02mimager (26)
Dichroic
(24)
Solar
input
Compensator
VIS/NIR-Quad Cell
Dichroic
Quad Cell
(21)
Lenses(20)
Laser
MetrologyDetection
1.02 m
filter (25)
0.525 mfilter (27)
Beam splitter
Fold
mirror
(15) Laser Metrology Insertion
MAESTRO
Interface (2)
PV InSb
Detector
Lens
Lens Glare stop
Dichroic
1.55 m
filter (19)
I t ti t S/C B
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Integration to S/C Bus
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Solar Occultation
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ACE Orbit
650 km,74
inclined
circularorbit
-90
-60
-30
0
30
60
90
25-Jul 24-Aug 23-Sep 23-Oct 22-Nov 22-Dec 21-Jan 20-Feb 21-Mar 20-Apr 20-May 19-Jun 19-Jul
La
titude
Day of Year
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Timeline Jan. 1998 Proposal to CSA
Feb. 2001 FTS and Imager CDR
Mar. 2001 MAESTRO CDR
Jun. 2001 Bus CDR Sept. 2002 S/C integration & test
Mar. 2003 Instrument test (Toronto)
May 2003 Final integration (DFL)
Aug. 2003 Launch
Sept. 2003 Commissioning
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ACE TestingScience testing led by Kaley Walker and Mike Butler
Integrate all instruments (FTS, MAESTRO and imagers)
and characterize their performance in a simulated
space environment
Science Test Objectives:
Determine performance of FTS using passive cooler
Make gas cell measurements using FTS / MAESTRO
Perform complete imager testing
Characterize suntracker pointing coordinates
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Instrument Calibration Facility (U of
Toronto)
Class 10000 clean-room with2.0 m diameter x 5.0 m Thermal Vacuum chamber
ICF Control room
TVAC window
Cold Shroud
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Testing the Passive Cooler
Detectors cooled to ~ 89 K by
directing the FTS passive cooler
at the He target
Multi-layer insulation (MLI)
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Gas cell measurements
to TVAC Window
3000C Blackbody
HgXe
lampGas
Cell
Gas Cell
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ACE-FTS Test Data & Results
InSb bandMCT band
Detector 89 K, Instrument Nominal Temperature, ~12.0 Torr N2O
N2ON2O
H2O
H2O
N2O
CO2
H2O
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ACE-FTS InSb Spectra
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400 420 440 460 480 500
Wavelength [nm]
-0.80
-0.60
-0.40
-0.20
0.00
Absorp
tionCellMeasurements[lo
g(I/Io)]
0.0
2.0
4.0
6.0
8.0
10.0
Smoothed
NOAACross-sections[Units1E-19cm
2]
U. Toronto Gas Cell
NO2 Absorption Spectrum
Hi-resolution Data from NOAASmoothed with 1.6 nm FWHMTriangular Filter
MAESTRO GasCell Data
MAESTRO Response to NO2
C.T. McElroy2003-04-03
Pegasus XL Launch Vehicle
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Pegasus XL Launch Vehicle
Pegasus XL Close up
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Pegasus XL Close-up
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FTS-2 (PARIS) in Quebec
W t l At h i
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Waterloo Atmospheric
Observatory Status of
Observatory Site:
Building completedAugust 2003.
WAO
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Conclusions ACE successfully launched Aug 12th, 2003.
The satellite is currently undergoing
commissioning.
Initial science measurements to hopefullyoccur toward the end of October, 2003.
Baseline duration of the mission is 2 years.