The Atmospheric Chemistry Experiment (ACE)

8/2/2019 The Atmospheric Chemistry Experiment (ACE)

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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


Altitude(km

)

CO Vmr Profile

0

20

40

60

80

100

120

0 50 100 150 200


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.

The Atmospheric Chemistry Experiment (ACE)

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