FACTORS GOVERNING THE SEASONAL VARIABILITY OF ATMOSPHERIC CARBONYL SULFIDE

Parv Suntharalingam

Harvard/Univ. of East Anglia

A.J. Kettle, S. Montzka, D. J. Jacob

GEOS-Chem Meeting

April 12th, 2007

Carbonyl Sulfide (COS) Uptake by Leaf During Photosynthesis

Can Carbonyl Sulfide help in Constraining Estimates of Global Primary Production ?

COSCO2

COS and CO2 are taken up through leaf stomata during photosynthesis

CO2

COS

GPP : Gross flux of CO2

converted to organic matter during photosynthesis

SEASONAL CYCLES OF COS and CO2

COS measurements : S. Montzka (NOAA-GMD)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.00 0.20 0.40 0.60 0.80 1.00

(X I

- X

mea

n)

/ X m

ean

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.00 0.20 0.40 0.60 0.80 1.00

BRW

ALT

MHD

LEF

HFM

NWR

MLO

KUM

CGOCO2 SH

COS

J F M A M J J A S O N D J F M A M J J A S O N D

Seasonal cycles of COS and CO2 are correlated, especially at forested sites.

CAN COS MEASUREMENTS CONSTRAIN BIOSPHERIC CO2 UPTAKE ?

Significant uncertainties remain on aspects of COS budget

SOURCES AND SINKS OF ATMOSPHERIC CARBONYL SULFIDE

COS

Mean atmospheric conc. ~ 500 ppt

SOURCES AND SINKS OF ATMOSPHERIC CARBONYL SULFIDE

ANTHROPOGENIC

OCEAN

CS2

DMS

COSOxidation

SOURCES AND SINKS OF ATMOSPHERIC CARBONYL SULFIDE

SOILS PLANTS ANTHROPOGENIC

OCEAN

CS2

DMS

COS

Tropospheric Oxidation, Stratospheric Photolysis

Oxidation

SOURCES AND SINKS OF ATMOSPHERIC CARBONYL SULFIDE

SOILS PLANTS ANTHROPOGENIC

OCEAN

CS2

DMS

COS

Tropospheric Oxidation, Stratospheric Photolysis

Oxidation

Biomass Burning

????

????

Uncertainty remains on source/sink fluxes

ATMOSPHERIC COS BUDGETKettle et al. [2002] : Gridded Fields

Not included here

Biomass Burning : 35 Tg S (8%) Stratospheric Photolysis : 16 Tg (3.5%) Minor sources : < 3%

ANNUALLY BALANCED BUDGET Total sources/sinks : 460 Gg S/year

-238 -130 -92

-180280

Also based on :

Chin and Davis, 1993; Watts, 2000

OUTLINE

1. Model atmospheric COS with recent best estimates of seasonal sources and sinks [Kettle et al. 2002]

2. Evaluate against measurements from global observation network [Montzka et al. 2006]

3. Which processes govern observed seasonal variability ? Can we improve estimates of prior COS fluxes?

AIM : Improved constraints on factors governing COS seasonal variability

COS SURFACE OBSERVATION NETWORK : NOAA-GMD Flask measurements since 2000 [Montzka et al. 2006]

Barrow (BRW)

Mauna Loa (MLO)

South Pole (SPO)

•

•

••

•

• • ••

•cgo

mhd

altbrw

kum mlo

smo

spo

nwr hfmlef

GEOS-Chem COS SIMULATION

INPUT FLUX DISTRIBUTIONS [Kettle et al. 2002]

SOURCES

•Ocean (Direct; CS2 and DMS oxidation to COS)

•Anthropogenic (Direct and CS2 oxidation to COS)

SINKS

•Terrestrial plant uptake

•Soil uptake

•COS oxidation by OH (tropospheric)

To be Implemented • Biomass burning•Stratospheric photolysis

GEOS-Chem Version 7-03-06

Resolution : 2x2.5; 30 vertical levels

Meteorology Year : 2001

COS SINK DISTRIBUTIONS [Kettle et al. 2002]

Plant Uptake (JAN)

Plant Uptake (JUL)

Soil Uptake (JAN)

Soil Uptake (JUL)

Plant fluxes derived from NPP and NDVI fields

Soil uptake based on soil moisture and temperature. (Only 1 soil type)

pmol/m2/sec

Anthropogenic (JAN)

Anthropogenic (JUL)

Ocean (JAN)

Ocean (JUL)

Anthropogenic COS fluxes distributed according to SO2 emissions (GEIA 1985)

Ocean fluxes based on ocean photochemical model and DMS distributions

COS SOURCE DISTRIBUTIONS [Kettle et al. 2002]

pmol/m2/sec

SEASONAL VARIABLITY OF COS FLUXESFlux Distributions : Kettle et al [2002]

AGGREGATED FLUXES

•N Hemisphere variability driven by plant uptake and ocean fluxes

•S Hemisphere variability driven by ocean fluxes

OCEAN

TOTAL SURFACE COS FLUX

PLANTSOILS

ANTH. OCEAN

Northern Hemisphere Southern Hemisphere

Gg

S p

er m

on

th

SEASONAL ANOMALIES AT MEASUREMENT SITESData : S. Montzka (NOAA-GMD)

South Pole Cape Grim, Tasmania

Barrow, Alaska Park Falls, Wisconsin

•Seasonal cycle has similar phase at Southern Hemisphere and Northern Hemisphere sites

•Northern Hemisphere sites show larger seasonal amplitude

Data for years 2001-2005

SEASONAL CYCLE AT REMOTE/OCEAN SITESObservations and Model : Seasonal Anomalies

•Good agreement at Southern Hemisphere remote/ocean sites

X Observations

Model

•Good agreement at Southern Hemisphere remote/ocean sites

•Observed seasonality not well reproduced as move northwards

X Observations

Model

SEASONAL CYCLE AT REMOTE/OCEAN SITESObservations and Model : Seasonal Anomalies

SEASONAL CYCLE AT TERRESTRIAL STATIONS Observations and Model : Seasonal Anomalies

Observed seasonal cycle not well

simulated at Northern Hemisphere terrestrial

sites

X Observations

Model

GLOBAL PLANT UPTAKE OF COS SUMMARY OF ESTIMATES : (Table 4 : Sandoval-Soto et al. 2005)

Units : Tg COS/year

Brown and Bell (1986) 2-5

Goldan et al. 1988 0.2-0.6

Kesselmeier and Merk (1993) 0.93 + 0.07

Chin and Davis (1993) 0.16-0.91

Watts (2000) 0.56 + 0.1

Xu et al. (2002) 2.3 + 0.5

Kettle et al. (2002) 0.39 – 0.5

Sandoval-Soto et al. (2005) 1.37-2.81

Kettle et al. [2002] NPP-based estimate is lower than recent estimates

SEASONAL CYCLE AT TERRESTRIAL SITES Increased Model Plant COS Uptake (Factor of 3)

X Observations

Original Model

Model: Increased

plant uptake

ORIG MODEL

INCREASED UPTAKE MODEL

Increased COS uptake by plants better matches observed seasonality

SEASONAL CYCLE AT TERRESTRIAL SITES Increased Model Plant COS Uptake (Factor of 3)

X Observations

Original Model

Increased

plant uptake

BUT

•Now need an additional source (for balanced annual budget)

SEASONAL CYCLE AT TERRESTRIAL SITES Increased Model Plant COS Uptake (Factor of 3)

X Observations

Original Model

Increased

plant uptake

BUT

•Now need an additional source (for balanced annual budget)

•Phase problems remain

SEASONAL CYCLE AT TERRESTRIAL SITES Increased Model Plant COS Uptake (Factor of 3)

X Observations

Original Model

Increased

plant uptake

BUT

•Now need an additional source (for balanced budget)

•Phase problems remain

•Missing source flux ?

SUMMARY

•Add source and sink for biomass burning and stratospheric photolysis

•Update anthropogenic COS emissions based on latest SO2 inventories.

•Inverse model analysis of COS measurements to improve source/sink flux estimates

•Primary influences on COS seasonal cycle : Ocean fluxes in Southern Hemisphere; Plant uptake and ocean fluxes in Northern Hemisphere.

•Increasing plant uptake of COS by a factor of 3 (to 0.7 Tg S/year) improves model representation of seasonal cycle at terrestrial sites

•But, annual COS budget no longer in balance – missing source ?

ONGOING/PLANNED WORK