Global isoprene sources and chemistry: constraints from atmospheric observations Daniel J. Jacob...
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Transcript of Global isoprene sources and chemistry: constraints from atmospheric observations Daniel J. Jacob...
Global isoprene sources and chemistry: constraints from atmospheric observations
Daniel J. Jacob
with Emily Fischer, Fabien Paulot, Lei Zhu, Eloïse Marais, Chris Miller
and funding from NASA, HUCE
Volatile organic compounds (VOCs) in the atmosphere:carbon oxidation chain
VOC RO2
NO2
O3
organicperoxyradical
NO
h
carbonyl R’O2
h
OH + products
organic aerosol
ROOHorganicperoxide
OHHO
2
OH, h
OH
products
EARTH SURFACE
biospherecombustionindustry
deposition
Increasing functionality & cleavage• sources of organic aerosol• sources/sinks of oxidants (ozone, OH)
Volatile organic compounds (VOCs) in the atmosphere:effect on nitrogen cycle
NOx
CH3C(O)OO
OH
EARTH SURFACE
combustion deposition
Reservoirs for long-range transport of NOx
lightning
deposition
HNO3
peroxyacetylnitrate(PAN)
other organic nitrates
NOx
OH
deposition
HNO3
Long-range atmospheric transport
RO2N fixation
hours
Why is isoprene such an important VOC?
Met
hane
Isop
rene
Oth
er b
iosph
ere
Anthr
opog
enic
Biomas
s bu
rning
0
200
400
600Global emission, Tg C a-1
1. Large emission:
2. Oxidation generates suite of volatile reactive products:
Isoprene
OH
~1 hmultistep
• Formaldehyde• Other carbonyls• Dicarbonyls• Peroxides• Epoxides• Isoprene nitrates
Contribution of isoprene to PANfrom GEOS-Chem global 3-D chemical transport model
Emily Fischer, Harvard
Anthropogenic
Open fires
Isoprene
Other biogenic VOCs
%
January July
Sensitivity of nitrogen deposition to isoprene emission
Sensitivity for Cayuhoga National Park (Ohio) computed with the GEOS-Chem adjoint
Local isoprene emission suppresses N deposition, upwind emission increases it
Fabien Paulot, Harvard
of local NOx
emission)
Estimating isoprene emissions: bottom-up and top-down approaches
Bottom-up estimate from plant model:EISOP = f(plant type, phenology, LAI, T, PAR, water stress, …)
Isopreneoxidationproducts
Ecosystem observations
Atmospheric observations
Top-down estimate from Inversion of chemical transport model:EISOP = f(atmospheric concentrations,transport, chemistry)
Observing isoprene oxidation products from space:formaldehyde (HCHO) and glyoxal (CHOCHO)
Scattering by atmosphereand Earth surface
l1
l2 HCHO orCHOCHOabsorptionspectrum
l1
l2
GOME (1995-2001), SCIAMACHY (2002-2012),OMI (2004-), GOME-2 (2006-) instruments
• Spectral fitting yields “slant” columns of HCHO, CHOCHO along light path• Air mass factor from radiative transfer model converts slant to vertical columns
HCHOCHOCHO
Annual mean vertical columns from GOME-2, 2007-2008
HCHO CHOCHO
Relating HCHO columns to VOC emission
VOCi HCHOh (340 nm), OHoxidation
k ~ 0.5 h-1
Emission Ei
displacement
In absence of horizontal wind, mass balance for HCHO column WHCHO:
i ii
HCHO
y E
k
yield yi
but wind smears this relationship depending on VOC lifetime wrt HCHO production:
Local linear relationshipbetween HCHO column and E
VOCsource Distance downwind
WHCHOIsoprene
a-pinenemethanol
100 km
detection limit
HCHO is mainly sensitive to isoprene emission with smearing ~ 10-100 km
Past use of HCHO vs. EISOP relationship over US to constrain isoprene emission with OMI data
OMI HCHO (Jun-Aug 2006)
OMI-constrained isoprene emission
GEOS-Chem local relationship betweenHCHO column and isoprene emission
Model slope (2400 s) agrees with INTEX-A vertical profiles (2300),
PROPHET Michigan site (2100)
Palmer et al. [2003, 2006}, Millet et al. [2006, 2008]
Temperature dominates variability of EISOP seen by OMIcan’t pick up any other variable from multivariate correlations, case studies
Lei Zhu, Harvard1 5 10 151015 molecules cm-2
HCHO column,Jun-Aug 2005
2006
2007
2008
Correlation of monthly mean HCHO with air T
NE Texas, JJA 2005-2008Exponential fitMEGAN
Daily data in Southeast US binned by air temperature
290 295 300 305 310 K
285 290 295 300 K
turnoverat 307 K
After 2009 it’s curtains for OMI…but GOME-2 provides consistent continuity
GOME-2 HCHO, 2007 OMI
June
July
August
GOME-2 vs. OMI correlationmonthly data in SE US JJA 2007-2008
Lei Zhu, Harvard
OMI 13x24 km2 13:30GOME-2 40x80 km2 9:30
nadir pixel time
slope = 0.91r2 = 0.82
Using OMI HCHOto constrain isoprene emissions in Africa
MODIS leaf area index MODIS fire counts Earth lights AATSR gas flares
1015 molecules cm-2
OMI annual meanHCHO slant columns
2005-2009
• Observed HCHO distribution over Africa points to sources from (1) biosphere, (2) open fires, (3) oil and gas industry
• Africa accounts for 20% of global biogenic isoprene emissions in MEGAN inventory…but based on little in situ data
Aug-Sep
Marais et al., in press
1015 molecules cm-2
Isolating biogenic HCHO in the OMI data• Exclude open fire (and dust) influence using MODIS
fire counts, OMI absorbing aerosol optical depth
• Exclude oil/gas industry influence using AATSR gas flare product
MODIS fire count > 0
OMI smoke AAOD > regional threshold
BIOMASS BURNING INFLUENCE (exclude)
NO
NO
YES
YES MODIS fire counts
OMI smoke AAOD
NO
OMI dust AAOD > 0.1 DUST INFLUENCE
(exclude) YES OMI dust AAOD
AATSR fire count > 0 ANTHROPOGENIC
INFLUENCE (exclude)
YES AATSR fire counts
OMI dust AAOD > 0.1 DUST INFLUENCE
(exclude) YES OMI dust AAOD
NO
BIOGENIC
(retain)
Marais et al., in press
HCHO slant columnoriginal data
HCHO vertical columnbiogenic only
air mass factor
HCHO slant column
HCHO biogenic vertical column;8-day product with 1ox1o resolution
OH
NO
O
HH
HO2
O
HO OH
-IEPOX
formaldehydeh
Pathways for HCHO formation from isoprene oxidation
RO2
OH
OH
IsomerizationC1,5 -shift
ROOH
• high-NOx branch (RO2+NO) yields fast HCHO as 1st generation product
Peeters
Paulot
O
MVK
O
MACR
Epoxydiols [Paulot et al., 2009]
More recently proposed low-NOx pathways regenerate OH, produce HCHO:
Isomerization [Peeters and Muller, 2010]
standardGEOS-Chemmechanism
first-generationhigh-NOx
low-NOx
• low-NOx branch (RO2+HO2 ) yields slower HCHO, depletes OH
OH
Time-dependent HCHO yield from isoprene oxidation
DSMACC box model calculations
aging/smearing
Yield is sensitive to NOx , not so much to mechanism except at very low NOx
Marais et al., in press
Boundary layer NOx levels over Africa
Annual NO2 tropospheric columns, fire influences excludedSatellite observations Model % isoprene RO2 reacting with NO
(GEOS-Chem, July)
• Boundary layer NOx over Africa is typically 0.1-1 ppbv• Expect NOx dependence of HCHO yield, moderate smearing
Marais et al., in press
boundary layer
Testing HCHO-isoprene smearing with AMMA aircraft data
Flight tracks (Jul-Aug 2006)and MODIS leaf area index Latitudinal profiles below 1 km
WIND
• HCHO tracks isoprene with only ~50 km smearing
• But NOx measured in AMMA was relatively high (mean 0.3 ppb)
OMI HCHO
Marais et al., in press
WIND
Smearing produces“shadow” region 200-300 km downwind of rainforest
Marais et al., in press
OMI HCHO column
1015 molecules cm-2
WIND
July
Testing HCHO-isoprene smearingin longitudinal transect across Congo:high isoprene and low NOx
shadow
Relationship between HCHO column and isoprene emission
Model sensitivity S of HCHO column (ΔHCHO) to isoprene emission (ΔEISOP) as function of tropospheric NO2 column (NO2)
StandardPaulot
• Use S = ΔHCHO / ΔEISOP for local OMI NO2 to derive isoprene emission• Exclude “shadow” regions on basis of anomalously high S values
Marais et al., in press
Error analysis on inferring EISOP from satellite HCHO data
Slant HCHO column
20% (spectral fitting)
Vertical HCHO column
20% (clouds, vertical distribution, albedo)
Isoprene emission
Estimated errors (8-day data, 1o x1o resolution)
15% (chemical mechanism)25-60% (smearing)15% (NO2 column)
• Total error: 40% (high-NOx ), 40-90% (low-NOx ). Can be reduced by averaging• Smearing is dominant error component. Need to resolve transport!
Marais et al., in press
Isoprene emission (12-15 local time annual mean, 2006)
Comparison of OMI isoprene emissions to MEGAN
MEGAN is too low for equatorial forest, too high for savanna
Marais et al., in press
2005-2009 monthly variability of isoprene emissionfor evergreen broadleaf forest of central Africa
Eloïse Marais, Harvard
• Variability is small and weakly correlated to temperature and LAI• Need to address uncertainty in meteorological and LAI products!
EISOP , temperature
EISOP , LAIAVHRR
2005-2009 monthly variability of isoprene emissionin open deciduous broadleaf forest of s. Africa
• May-Sept dry season; LAI drops below 1 in Aug, driving EISOP down• Sept-Nov increase in LAI (greening) causes spike in EISOP • Wet season cloudiness causes T to decrease after Nov, driving EISOP down
even though LAI continues to increase• Suggests saturation of EISOP when LAI exceeds 1.5 Eloïse Marais, Harvard
EISOP , temperature
EISOP , LAI
Jan Jan Jan
AVHRR
Glyoxal from space as additional constraint on VOC sources
GOME-2
• Glyoxal sources in GEOS-Chem:55% isoprene, 24% acetylene, 7% aromatics, 8% fire emission, 2% monoterpenes
• Glyoxal lifetime ~1 h (photolysis)
Chris Miller, Harvard
• Operational data available from SCIAMACHY, GOME-2
• OMI retrieval in progress (Chris Miller, Harvard)
GEOS-Chem
Does glyoxal provide information complementary to HCHO?
GOME-2
GEOS-Chem
Glyoxal columns (Jun-Aug 2007) Glyoxal/HCHO column ratio
GOME-2 shows variability in glyoxal/HCHO ratio that GEOS-Chem doesn’t capture
Chris Miller, Harvard
Glyoxal production from isoprene
Observed fast production with 2-3% yield [Galloway 2011] – Dibble isomerization?
Chris Miller, Harvard
Dibble isomerization
first-generation
Tower data from CABINEX, northern Michigan (Jul-Aug 09)
Measured GEOS-Chem with EISOP /2
isoprene
Glyoxal
Pathways forglyoxal formation
Dibble
Observations by Frank Keutsch
Dibble isomerization is dominant model pathway for glyoxal formation
Chris Miller, Harvard
OH-aldehydes
Vision for the future: ecosystem monitoringAdjoint inversion of isoprene emission using geostationary satellite observations of HCHO and glyoxal
HCHO, glyoxalmeasurement
(x, t)1-km chemicaltransport model
inverse model
Emission
E( x’, t’)
• Geostationary observation diurnal information, higher precision daily data GEMS (Korea), 2017; Sentinel-4 (Europe), 2019; GEO-CAPE (US), 2020+• Adjoint inversion solve smearing problem, allow isoprene emission monitoring need to properly represent chemistry-transport coupling on scales of PBL mixing
Wind
boundary layermixing (~1 h)