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