GEOS-CHEM Meeting 2005Dylan Millet

Variability of CH2O during ICARTT:

Implications for GOME/OMI

Dylan Millet

GEOS-CHEM Users’ MeetingApril 2005

GEOS-CHEM Meeting 2005Dylan Millet

Use ICARTT flight data to address:

• Satellite retrievals– Is GEOS-CHEM accurately representing the

CH2O vertical profile (shape factor)?

– What is the uncertainty/bias in the AMF?

• Variability in CH2O– What are the dominant sources of CH2O

over N.A.?– Implications for satellite retrievals?

GEOS-CHEM Meeting 2005Dylan Millet

Air Mass Factor

d

0

1

)()( dSwAMFAMF GAMFG: Geometric factor

w(): Scattering weights

~ -(lnIB)/

S(): Shape factor

Normalized vertical distribution

From model

AMF: Slant column / vertical column

GEOS-CHEM Meeting 2005Dylan Millet

All profiles

E. U.S.

Atlantic

Vertical Profile Comparison

24

68

10

0 1000 2000 3000 4000CH2O [ppt]

Z (

km)

NCARURIGEOS-CHEM

24

68

10

0 1000 2000 3000 4000CH2O [ppt]

Z (

km)

NCARURIGEOS-CHEM

24

68

10

0 1000 2000 3000 4000CH2O [ppt]

Z (

km)

NCARURIGEOS-CHEM

GEOS-CHEM Meeting 2005Dylan Millet

Clear Sky AMF Comparison- all profiles -

Small negative bias (-6%) in modeled clear sky

AMF-60 -40 -20 0 20 40 60

02

46

8

100*{AMF(mod)-AMF(meas)}/AMF(mod)

Mean bias: -5.8%SD: 15.3%SE: 2.2%n = 47

GEOS-CHEM Meeting 2005Dylan Millet

Continental profiles: -7%

Oceanic profiles: +5%

GEOS-CHEM Meeting 2005Dylan Millet

Cloudy AMF Comparison

Clouds:Can act to increase or decrease sensitivity of measurement

GEOS-CHEM Meeting 2005Dylan Millet

Cloudy AMF Comparison

Actual cloud

profile:

Retrieved

cloud:

GEOS-CHEM Meeting 2005Dylan Millet

Cloudy AMF Comparison

Accounting for clouds:

Small negative bias persists, larger spread

-600 -400 -200 0

05

1015

2025

100*{AMF(mod)-AMF(meas)}/AMF(mod)

Mean bias: -24.7%SD: 96.6%SE: 14.1%n = 47

Median bias: -5.6%(-27.8-+4.5%)

GEOS-CHEM Meeting 2005Dylan Millet

Continental profiles: -17%

Oceanic profiles: +3%

GEOS-CHEM Meeting 2005Dylan Millet

CH2O Sources & Variability

GEOS-CHEM Meeting 2005Dylan Millet

500 1000 1500

0.0

0.2

0.4

0.6

0.8

1.0

[CH2O] (ppt)

P(i)

/P(t

otal

)

Oceanic

OtherNMHCsOVOCsMethaneIsoprene

0 500 1000 1500

0.0

0.2

0.4

0.6

0.8

1.0

[CH2O] (ppt)

P(i

sopr

ene)

/P(t

otal

)

Oceanic

0 1000 2000 3000 40000.

00.

20.

40.

60.

81.

0[CH2O] (ppt)

P(i

sopr

ene)

/P(t

otal

)

Continental

0 1000 2000 3000

0.0

0.2

0.4

0.6

0.8

1.0

[CH2O] (ppt)

P(i)

/P(t

otal

)

Continental

OtherNMHCsOVOCsMethaneIsoprene

CH2O Sources

Importance of measured precursors to CH2O production:

ii

ii

total

i

Yik

Yik

P

P

GEOS-CHEM Meeting 2005Dylan Millet

0.0 0.2 0.4 0.6 0.8

02

46

810

P(isoprene)/P(total)

Z (

km)

Oceanic

0.0 0.2 0.4 0.6 0.8

24

68

10

P(isoprene)/P(total)

Z (

km)

Continental

0.0 0.2 0.4 0.6 0.8 1.0

24

68

10Z

(km

)

P(i)/P(total)

Continental

OtherNMHCsOVOCsMethaneIsoprene

CH2O Sources

0.0 0.2 0.4 0.6 0.8 1.0

24

68

10Z

(km

)

P(i)/P(total)

Oceanic

OtherNMHCsOVOCsMethaneIsoprene

GEOS-CHEM Meeting 2005Dylan Millet

CH2O SourcesContinental boundary layer:

Continental BL:

• P(isoprene) ~ 50% of P(total) on average

• OVOCs, methane important

• Variability in P(isoprene) > 10x P(others)

0 5 10 15 20

010

020

0 IsopreneMean: 3.25SD: 4.8

0.0 0.5 1.0 1.5 2.0

040

80 OVOCMean: 0.51SD: 0.26

0.20 0.22 0.24 0.26 0.28

010

30

MethaneMean: 0.25SD: 0.02

0.0 0.5 1.0 1.5

040

80

NMHCMean: 0.17SD: 0.16

Cou

nts

P(i) (1/s)

GEOS-CHEM Meeting 2005Dylan Millet

Conclusions

• Error in AMF:– Uncertainty of ±30% (2) for an

individual clear-sky scene (higher for cloudy-sky)

– Mean bias ~ -7% continental clear-sky; -17% continental cloudy-sky

• Sources of CH2O:– Isoprene, OVOC, methane dominant

sources over N.A.– Variability in isoprene source > 10x

that of other sources