Dylan MilletHarvard University

with

D. Jacob (Harvard), D. Blake (UCI), T. Custer and J. Williams (MPI),J. de Gouw, C. Warneke, and J. Holloway (NOAA), T. Karl (NCAR),

H. Singh (NASA), B. Sive (UNH)

New Constraints on Terrestrial and Oceanic Sources of Atmospheric Methanol

NASA Atmospheric Chemistry Program

NOAA C&GC Postdoctoral

Fellowship Program

American Geophysical Union Fall Meeting 2007

Thanks to:

Methanol: The Most Abundant Non-Methane Organic Gas

CH3OHBurden: ~4 TgLifetime: 5-10

d

CH4

Plant Decay

Biomass Burning

Atmospheric

Production

Dry Dep (Land)

Wet Dep

Oxidation by OH

Source of CO, HCHO,

O3

Sink of OH

Plant Growth

Ocean Exchange

Urban Emission

s ?

Aircraft and Surface Measurements Used to Constrain Methanol Sources & Sinks

New plot with all obs

AIRCRAFTPEM-TB, INTEX-A/B, MILAGRO, ITCT-2K2/2K4, TOPSE, LBA/CLAIRE, TROFFEE, TEXAQS-II

SURFACEOOMPH, NEAQS-2K2, Kinterbish, Tennessee, UMBS, Trinidad Head, Duke Forest, Chebogue Pt, Appledore Isl., Thompson Farm, Rondônia, Amazonas

GEOS-Chem 3D model of atmospheric chemistry

GEOS-Chem 3D model of atmospheric chemistry

Interpret with:

Methanol: The Most Abundant Non-Methane Organic Gas

CH3OHBurden: ~4 TgLifetime: 5-10

d

CH4

Plant Decay

Biomass Burning

Atmospheric

Production

Dry Dep (Land)

Wet Dep

Oxidation by OH

Source of CO, HCHO,

O3

Plant Growth

Ocean Exchange

Urban Emission

s

Ocean Mixed Layer (OML): Source + Sink for Atmospheric Methanol

Previous work:· Assume constant OML undersaturation· OML a small net sink Assumes air-sea exchange controls [CH3OH]OML

Ocean Mixed Layer (OML): Source + Sink for Atmospheric Methanol

Recent OML Measurements imply a large methanol reservoir(20× that of the atmosphere)

Biotic consumption ~ 3 d

[Heikes et al., 2002]

CH3OH120 ± 50 nM

[Williams et al., 2004]

66 Tg

Short lifetime requires large OML source (~8E3 Tg/y)

Ocean Mixed Layer (OML): Source + Sink for Atmospheric Methanol

Recent OML Measurements imply a large methanol reservoir(20× that of the atmosphere)

100 Tg/y OML ventilationweeks-months

Biotic consumption ~ 3 d

[Heikes et al., 2002]

CH3OH120 ± 50 nM

[Williams et al., 2004]

66 Tg

Biological production

Short lifetime requires large OML source (~8E3 Tg/y) Transfer from atmosphere insufficient to balance loss Large in-situ biological source implied

Ocean Mixed Layer (OML): Source + Sink for Atmospheric Methanol

Recent OML Measurements imply a large methanol reservoir(20× that of the atmosphere)

100 Tg/y OML ventilationweeks-months

Biotic consumption ~ 3 d

[Heikes et al., 2002]

CH3OH120 ± 50 nM

[Williams et al., 2004]

66 Tg

Biological production

Short lifetime requires large OML source (~8E3 Tg/y) Transfer from atmosphere insufficient to balance loss Large in-situ biological source implied Ocean emission, uptake: independent terms in atmospheric budget

Ocean Emission and Uptake of Atmospheric Methanol

Marine biosphere: large source of atmospheric methanol

Comparable to terrestrial biota

Ocean Emission

85 Tg y-1

Ocean Uptake

Comparable to oxidation by OH

Calculate ocean source & sink terms independently· On basis of measured OML concentrations

100 Tg y-1 =11 d

Net Flux

New Air-Sea Flux Parameterization Generally Consistent with Atmospheric Observations

Measured vs. modeled methanol concentrations over the S. Atlantic

OOMPH 2007

MeasuredModeled

Methanol profiles over the Pacific

Methanol Emissions from the Terrestrial Biosphere

Aircraft Measurements Reveal Overestimate of Plant Growth

Source

All plants make methanol

· Produced during cell growth· Emitted from leaves ~ f(T, hν)

· E = 0.11% × NPP [Galbally & Kirstine, 2002]

Simulated summer methanol concentrations in surface air

[ppb]

MeasuredModeled

Vertical Profiles over N. America

Broad-scale inflow to W. US well simulated

2× BL overestimate during summer Only explained by overestimate of plant growth source

Bias Correlates Spatially with Regions of High Broadleaf Tree & Crop Coverage

ObservedModeled

Boundary Layer Methanol Concentrations [ppb]Modeled - Measured

Removal of bias requires:

4x reduction of broadleaf tree + crop emissions, or 2x reduction of emissions from all terrestrial plants

MDVD2 vegetation coverage [Guenther et al., 2006]

Reduced Biogenic Source Yields Better Agreement over North America and Tropical South America

MeasuredBase case 2× (all plants) 4× (bdlf trees + crops)

Vertical Profiles over N. America Amazon Boundary Layer

Base case2×

all plants4×

bdlf trees, cropsMeasured

Both optimizations of comparable quality

Best estimate of global terrestrial biogenic source:

80 Tg/y(vs. 145 Tg/y base

case)

Importance of Biogenic vs. Anthropogenic Sources

Methanol strongly correlated with CO despite lack of large anthro. source

Aircraft measurements over N. America during summer

Model captures correlation, slope (with independent constraints on CO)

MeasuredBase case 2× (all plants) 4× (bdlf trees + crops)

Updated Global Budget of Atmospheric Methanol

Sources Sinks

108 molec/cm2/s 108 molec/cm2/s

85 Tg/y 80 Tg/y

37 Tg/y 23 Tg/y

12 Tg/y 5 Tg/y

101 Tg/y 88 Tg/y

40 Tg/y 13 Tg/y

Atmospheric lifetime: 4.7 days