Global Distributions of Carbonyl Sulfide Global Distributions of Carbonyl Sulfide (OCS) in the Upper Troposphere and (OCS) in the Upper Troposphere and

StratosphereStratosphereMichael Barkley & Paul Palmer, University of EdinburghChris Boone & Peter Bernath† , University of Waterloo (†University of York)Parvadha Suntharalingham, UEA & Harvard University

Michael Barkley, University of Edinburgh

Slide 2

Outline

Introduction♦ A quick tour of the OCS world - why is OCS important?

ACE retrievals of OCS ♦ What does the raw data tell us?

Validation - comparisons of ACE OCS to other OCS measurements♦ ACE vs. ATMOS v3 data (Shuttle-borne high resn. FTIR) ♦ ACE vs. MkIV data (Balloon-borne high resn. FTIR)

Global Distributions♦ Global Maps♦ Zonal means & latitudinal profiles♦ Estimate of OCS stratospheric Lifetime

Summary

Michael Barkley, University of Edinburgh

Slide 3

Why is OCS interesting & important?

Most long-lived and abundant sulphur gas in the atmosphere

OCS oxidised in stratosphere to form sulfate aerosol - which supposedly ‘sustains’ the Stratospheric Sulfate Aerosol layer (SSA)♦ Attenuation of UV radiation♦ Surface for heterogeneous

chemistry More recently: uptake of OCS

by plants is very similar to uptake of CO2

♦ Can OCS constrain GPP/biospheric fluxes of C?

Uncertainty in budgetOCS seasonal cycle similar to CO2

Michael Barkley, University of Edinburgh

Slide 4

OCS Global Budget

CS2

SO2 AerosolsStratosphere

Troposphere

41 (154)

-130 (56)

-238 (30)

64 (32)CS2DM

S

154 (37)

84 (54)

116 (58)

70 (50)

Kettle et al., JGR, 2002: Forward modelling approach: calculate global COS fluxes as sum of individual fluxes from sources & sinks

SO2 OCS

OCS

OCS(~2.5Tg)

OCS(~0.3Tg)

0.31Tg 0.34Tg

~9%

Chin & Davis, JGR, 1995Flux (error) [Gg S]

Atmospheric Losses:

OH: -94 (12)

O: -11 (5)

hv: -16 (5)

---------

Tot: -121 (14)

Michael Barkley, University of Edinburgh

Slide 5

Source/sink seasonal variability

Seasonal cycle determined by:♦ NH: Vegetation and ocean♦ SH: Ocean

Sources & sinks drive variability in lower atmosphere

Kettle et al., JGR, 2002: Forward modelling approach: calculate global COS fluxes as sum of individual fluxes from sources & sinks

Suntharalingham et al, 2008

Michael Barkley, University of Edinburgh

Slide 6

ACE OCS retrievals

Use improved v2.2 ‘research products’♦ More micro-windows &

higher altitudes Uses HITRAN 2004 8 interfering species fitted

simultaneously:

♦ OCS ♦ Isotopologue 2

♦ O3

♦ Isotopolgues 1 & 3

♦ CO2

♦ Isotopolgues 1,2,3 & 4

♦ H2O

Centre [cm-1]

Width [cm-1]

Low-z [km]

High-z [km]

2039.01 0.4 6 to 8 19 to 26

2040.50 0.5 8 to 10 20 to 26

2043.51 0.4 10 to 12 20 to 26

2044.01 1.4 17 22 to 31

2045.18 0.3 6 to 8 22 to 31

2048.03 0.4 6 to 8 23 to 31

2049.95 0.4 16 to 18 23 to 31

2051.30 0.4 6 to 8 23 to 31

2053.21 0.3 13 to 15 23 to 31

2054.45 0.5 12 to 15 23 to 31

2055.90 0.5 6 to 8 12 to 15

2057.52 0.45 6 to 8 12 to 15

Low z = 8 – 2 x [sin(lat)]2

Fitting windows

Pole to Equator

Michael Barkley, University of Edinburgh

Slide 7

ACE OCS

Total # occultations = 10251

No data below ~6 km or above ~31 km

Few measurements > 600 pptv

Michael Barkley, University of Edinburgh

Slide 8

ACE vs. MkIV Balloon ProfilesMkIV data courtesy of Geoff Toon, JPL, NASA

Michael Barkley, University of Edinburgh

Slide 9

ACE measurements (not) near Fort Sumner

Michael Barkley, University of Edinburgh

Slide 10

Comparing ACE to ATMOS: where & when?

Michael Barkley, University of Edinburgh

Slide 11

ACE vs. ATMOSATMOS data courtesy of JPL, NASA

Michael Barkley, University of Edinburgh

Slide 12

Some useful numbers…

Differences most likely due

to improvements

in spectroscopic parameters @ 5

microns

ACE – HITRAN 2004

ATMOS – Atmos line list

ATMOS ~ 10% > ACE

Michael Barkley, University of Edinburgh

Slide 13

ACE OCS Global Distributions (2004-2006)

Michael Barkley, University of Edinburgh

Slide 14

Zonal Seasonal Means

Profiles averaged in 15°latitude bins; only bins with a minimum of 10 profiles are plotted.

Distributions largely determined by atmospheric transport

Michael Barkley, University of Edinburgh

Slide 15

Zonal Seasonal Means

Profiles averaged in 15°latitude bins; only bins with a minimum of 10 profiles are plotted.

HCN

HCN

HCN

CO

CO

CO

Michael Barkley, University of Edinburgh

Slide 16

Zonal Seasonal Means

Profiles averaged in 15°latitude bins; only bins with a minimum of 10 profiles are plotted.

Data from: Atlantic cruises + Atlas-3

Notholt et al., Science, 2003

Michael Barkley, University of Edinburgh

Slide 17

Seasonal Maps at 9.5 km

Michael Barkley, University of Edinburgh

Slide 18

Seasonal Maps at 9.5 km

INTEX-A 1st July – 14th August 2004 (Blake et al. 2008)

Michael Barkley, University of Edinburgh

Slide 19

Mean Latitudinal Profiles

Michael Barkley, University of Edinburgh

Slide 20

Mean Latitudinal Profiles

Michael Barkley, University of Edinburgh

Slide 21

OCS stratospheric lifetime

Long-lived trace gases in stratosphere are linearly correlated provided lifetime of one species is known, the lifetime of the other can be estimated [see Plumb & Ko, 1992]

T1 = T2 x (dΩ2/dΩ1) x (Ω1/Ω2)

Use coincidental ACE measurements of CFC-11 and CFC-12 + & CFC lifetimes & tropospheric VMRs from the WMO 2006 report: ♦ CFC-11 (CFCl3)

♦ Ω = 254 pptv, T=45±10 yrs♦ CFC-12 (CF2Cl2)

♦ Ω = 540 pptv, T=100±20 yrs Tropospheric OCS = 500 pptv

♦ Note, don’t use ACE value as it represents UT

Michael Barkley, University of Edinburgh

Slide 22

Some more useful numbers…

Best estimate = 64±21 yrs

Michael Barkley, University of Edinburgh

Slide 23

What does the stratospheric lifetime tell us?

‘Back of envelope’ calculation♦ OCS stratospheric sink =

total mass of OCS in atmosphere / stratospheric lifetime Using the best estimate for OCS lifetime = 64±21 yrs

♦ OCS stratospheric sink = 63 – 124 Gg OCS / yr♦ = 34 – 66 Gg S / yr

No OCS source in strats sink = tropospheric flux Tropospheric sulfur flux (in the form of OCS) required

to sustain the stratospheric sulfate aerosol layer (see Chin and Davis, JGR, 1995 & references therein)♦ = 30 – 170 Gg S / yr

i.e., our estimate is at the lower end of this range Answer: Need to re-examine OCS contribution to SSA

using ACE data and stratospheric sulfur/aerosol model

Michael Barkley, University of Edinburgh

Slide 24

What does the stratospheric lifetime tell us?

‘Back of envelope’ calculation♦ OCS stratospheric sink =

total mass of OCS in atmosphere / stratospheric lifetime Using the best estimate for OCS lifetime = 64±21 yrs

♦ OCS stratospheric sink = 63 – 124 Gg OCS / yr♦ = 34 – 66 Gg S / yr

No OCS source in strats sink = tropospheric flux Tropospheric sulfur flux (in the form of OCS) required

to sustain the stratospheric sulfate aerosol layer (see Chin and Davis, JGR, 1995 & references therein)♦ = 30 – 170 Gg S / yr

i.e., our estimate is at the lower end of this range Answer: Need to re-examine OCS contribution to SSA

using ACE data and stratospheric sulfur/aerosol model

Michael Barkley, University of Edinburgh

Slide 25

Summary

OCS important but large uncertainties in budget remain ACE has provided the first global OCS UT/stratosphere

distributions observed from space♦ Generally good agreement with other OCS measurements♦ Distributions governed by atmospheric transport ♦ Biomass burning is a significant source in SH tropics…

♦ …but is it weaker than previously thought?

Strong correlations with CFC-11 & CFC-12 yields: ♦ OCS stratospheric lifetime = 64 ± 21 yrs♦ OCS stratospheric sink = 63 – 124 Gg OCS / yr

Next step, (someone) must incorporate ACE OCS measurements into global CTM

Results submitted to GRL paper (in revision)

EndEnd

Michael Barkley, University of Edinburgh

Slide 27

ACE vs. Aircraft

GMD NOAA aircraft flights (grey lines) constrained to region: ♦ 40 - 48 °N♦ 89 - 104.3 °W

ACE sampled over:♦ 25 - 55 °N♦ 70- 125 °W♦ Necessary to get ACE

data down to ~8 km Construct mean aircraft

profile (red line) Interpolate across altitude

gap (if necessary) and smooth (light green line)

First complete trop-strat OCS profiles!

Aircraft data courtesy of Stephen Montzka GMD, NOAA

Michael Barkley, University of Edinburgh

Slide 28

Summary of MkIV and ATMOS instruments

MkIV ♦ Balloon-borne high

resolution FTIR ♦ Covers 650-5650 cm-1

spectral region at 0.01 cm-1 resolution

♦ Solar Occultation ATMOS

♦ Atmospheric Trace Molecule Spectroscopy experiment

♦ Balloon-borne high resolution FTIR

♦ Covers 600-4800 cm-1 spectral region at 0.01 cm-1 resolution

♦ Solar Occultation

Michael Barkley, University of Edinburgh

Slide 29

Finely balancing the OCS global budget

Total sources = 592 (166-1071)† [210-1049]*

Total sinks = 489 (380-597) † [902-1827]*

♦ † = Suntharalingham et al, JGR (sub), 2007 (GEOS-Chem)♦ * = Montzka et al, JGR, 2007 (Observations + Kettle fluxes)

“…within the large associated range of uncertainties..”

Kettle et al., JGR, 2002: Forward modelling approach: calculate global COS fluxes as sum of individual fluxes from sources & sinks

Michael Barkley, University of Edinburgh

Slide 30

Past Variability

Sulfur emissions?

Deforestation?

Viscose rayon production of CS2?

Little Ice Age 1550-1850 AD

Drop not understood

Montzka et al., JGR, 2004