Sensitivity of continental boundary layer chemistry to a new isoprene oxidation mechanism
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Transcript of Sensitivity of continental boundary layer chemistry to a new isoprene oxidation mechanism
Sensitivity of continental boundary layer chemistry to a new isoprene oxidation mechanism
Jingqiu Mao (Harvard), Fabien Paulot (Caltech), Daniel Jacob (Harvard), Paul Wennberg (Caltech), Ronald Cohen (UC Berkeley)
and funding from NASA ACMAP
temperature, radiation, land use
Human activity
Air Quality
climate
ozone, aerosols
Biomass burning
isoprene emission
Lightning
Isoprene Emissions Affect Atmospheric Composition and Climate
Isoprene Methanol An-throVOC
0200400600
Global Emissions (Tg/yr)
Intercontinental Chemical Transport Experiment –North America Phase A (INTEX-A)
GEOS-Chem chemical transport model- GEOS-5 assimilated met field- 1 year spin up at 2x2.5 degree- New lightning vertical distribution based on Ott et al. (2010).- Rescaled CO emission based on Kopacz et al. (2010).
We use a new isoprene oxidation mechanism to test our understanding of isoprene chemistry, mainly based on two recent papers - Paulot et al., ACP, 2009- Paulot et al., Science, 2009
Better understand underestimated OH in boundary layer (Ren et al., 2008)
Better understand the discrepancy between OMI and MEGAN isoprene emissions over US (Millet et al., 2008)Millet et al. (2008)
From July 1st to August 15th of 2004
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OH
OH
OO
OHOO
OH
OH
OHOO
OH
OHOO
O2
O2
O2
O2
NO/O2
-hydroxyl (E/Z)
-hydroxyl (E/Z)
-hydroxyl
-hydroxyl
O
methyl vinyl ketone(MVK)
O
methacrolein(MACR)
NO/O2
+ HCHO
+ HCHO
ISOPN (1,2)
ISOPN (1,4)
ISOPN (4,1)
ISOPN (4,3)
O
OH
NO/O2
OH
O
HC5
+ GLYC + MGLYX
+ HACET + GLYX
Isoprene high NOx scheme NO/O2
HC5
41%
14%
15%
23%
OH on 2, 3 are not shown here since it only accounts for 7%
24%
24%
6.7%
6.7%
1. The yield of first generation isoprene nitrates is 11.7%.2. -hydroxyl channel accounts for 30% of OH+ isoprene reaction flux.3. First generation of HACET, GLYC, GLYX and MGLYX (not just from MACR).4. MVK and MACR are only produced through ß-channel.
OH
ONO2
ISOPN (1,4)
OH/O2 NOO
HO
hydroxyacetone(HAC)
O
+
OH
ONO2
methylvinylketone nitrate (MVKN)
+ O2NO O
ethanal nitrate(ETHLN)
+ H
O
H
HCHO
ONO2
OH
ISOPN (4,1)
OH/O2 NO
OH
O
glycolaldehyde(GLYC)
+O2NO
O
propanone nitrate(PROPNN)
+
HCHO
O
dihydroxylbutanone(DHB)
OHOH
+
OHONO2
OH/O2 NO
ISOPN (1,2)
O
HO
hydroxyacetone(HAC)
+OH
O
glycolaldehyde(GLYC)
O
methacrolein nitrate(MACRN)
+ONO2
OHHCHO
+
OHONO2
ISOPN (4,3)
OH/O2 NO
O
HO
hydroxyacetone(HAC)
+OH
O
glycolaldehyde(GLYC)
O
+
OH
ONO2
methylvinylketone nitrate (MVKN)
HCHO
+ H
O
H
H
O
H
H
O
H
photochemical lifetime of isoprene nitrates (OH = 3x106 molecules cm ):(-ISOPN) ~ 7hr > (-ISOPN) ~ 1hr
Fate of isoprene nitrates (NOx reycling = 55%)
NO2
68%
NO2
68%
NO2
45%
NO2
56%
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34
OH
OH
OO
OHOO
OH
OH
OHOO
OH
OHOO
O2
O2
O2
O2
-hydroxyl (E/Z)
-hydroxyl (E/Z)
-hydroxyl
-hydroxyl
Isoprene low NOx scheme
41%
14%
15%
23%
OH on 2, 3 are not shown here since it only accounts for 7%
HO2
HO2
HO2
HO2
OH
OOH
OHOOH
OOH
OH
OHOOH
MVK + HCHO + OH
MACR + HCHO + OH
17%
17%
OH
OH
OH
OH
OH
O
OH
OH
OOH
+ OH
+ OH
OHO
OH
+ OH
+ OH
OH OH
O
IEPOX
IEPOX
IEPOX
IEPOX
photochemical lifetime (IEPOX) ~ 6hr (OH=3x106 molecule cm-3, T=298K)IEPOXOO will decompose to HAC, GLYC, GLYX, MGLY
ISOPOOH
ISOPOOH
ISOPOOH
ISOPOOH
SOA precursor
OHOO
RIO2
+ HO2
0.12 OH
OH recycling from HO2+RO2 reactions
OOO
OH
VRO2
+ HO2 0.68 OH+ HO2 0.98 OH
O
OHOO
MRO2
ISOPOOH
1.0 OH
IEPOXOH
IEPOXOOHO2
1.125 OH
O
MVK
OH
O
MACR
OH
OHO
OOMAO3
+ HO2 0.87 OH
VRP
10%MRP
2%
MAOP
10%
O
ATO2
OO+ HO2 0.15 OH
85%
ATOOH
O
MCO3/RCO3
OO + HO2 0.44 OH
56%
RCOOH+RP
(Dillion et al., 2008)
(Paulot et al., 2009)
(Crounse et al., 2010, in prep)
Median vertical profiles in INTEX-A (Observation vs. model)
INTEXA
PROPHET
Ren et al. (2008)
Observed OH/ modeled OH in continental boundary layer
The underestimated OH at high isoprene condition is reproduced in default chemistry.
This is remarkably improved in new isoprene chemistry.
Observational constraints on isoprene nitrates
Slope=0.119
Perring et al. (2009)
Slope=0.114
The slope (Isoprene Nitrates vs. HCHO) in the observation is well captured by the model.
This slope is fairly robust in the new isoprene chemistry with various IN+O3 rates
Model with new isoprene chemistryObservation HCHO vs. Alkyl Nitrates
Speciation of isoprene nitrates in the model
The offset may be from other organic nitrates.
The majority of isoprene nitrates are from the second generation products (PROPNN, MVKN etc.).
The vertical profile is insensitive to the deposition velocity of the first generation products (mainly driven by chemical loss).
The vertical profile is insensitive to the rates of IN+O3, only changing the relative distribution of these organic nitrates.
τ (OH) τ (ozone)
δ-ISOPN 1hr 5hr
β-ISOPN 7hr 2hr
HCHO yield at different NOx conditions (new isoprene chemistry vs. default GEOS-Chem mechanism)
Default GEOS-Chem mechanism is mainly from Horowitz et al. (1998)!!!!
Two mechanisms show similar HCHO yield at NOx=1ppb and 0.1ppb, since HCHO is mainly produced through β-hydroxyl channel.
Prompt HCHO formation, important for deriving isoprene emission from satellite observations.
Difference at NOx=0.01ppb is mainly due to the yield from ISOPOO+HO2.
Computed in a photochemical box model. Initialized with 1ppb isoprene.O3 (40ppb), CO (100ppb), and NOx are held constant.
0-2 km
2-4 km 6-8 km
4-6 km
overestimate of ozone
ppb
new isoprene chemistry – default chemistry
Too much lightning NOx? (6 Tg/yr)Too much isoprene emissions? (MEGAN)Halogen chemistry?
Extra slides
Deposition for new tracersHeff (moles L-1 atm-1 ) ΔH/R (K) Reference
HCOOH 167,000 (pH = 5) -6100 Ito et al., 2007
CH3COOH 11,400 (pH = 5) -6300 Ito et al., 2007
MOBA 23,000 -6300 Ito et al., 2007
GLYC 41,000 -4600 Ito et al., 2007
GLYX 360,000 -7200 Schweitzer et al., 1998
MGLY 3,700 -7500 Ito et al., 2007
δ-ISOPN 17,000 -9200 Ito et al., 2007
β-ISOPN 17,000 -9200 Ito et al., 2007
MACRN 17,000 -9200 Ito et al., 2007
MVKN 17,000 -9200 Ito et al., 2007
PROPNN 1000 0 R. Sander (NITROOXYACETONE)
RIP 83,000 -7400 use H2O2
IEPOX 83,000 -7400 use H2O2
MAP 840 (f0 =1, reactive) -5300 R. Sander
HNO3 210,000 -8700
OH in July of 2004(average between 10am-2pm)
Global impact on OH
Impact on OH is more significant in tropics.Global annual mean OH increase by 10-20%.
Ren et al. (2008)
Obs
model
Consistent with underestimated HO2 in the box model, which does not have OH recycling from RO2+HO2 .
GEOS-Chem (chemical transport model)
• GEOS-5 assimilated met field• 1 year spin up at 2x2.5 degree• New lightning vertical distribution based on
Ott et al. (2010)• Rescaled CO emission based on Kopacz et
al. (2010)• Updated reaction rates with JPL06 and
IUPAC06• Updated photolysis cross sections and
quantum yield with Fast-JX• Non local PBL mixing• LINOZ cross tropopause ozone flux
OH budget in continental boundary layer(new isoprene chemistry vs. default GEOS-Chem mechanism)
Major difference is from HO2+NO (mainly from HO2).
RO2+HO2 does not contribute much, since it cannot compete with NO when NO is about 100 ppt.
Why is HO2 higher in new isoprene chemistry?
default chemistry new isoprene chemistry
defaultchem
new isoprene
OH recycling from HO2+RO2 increases HOx and thus OH (through HO2+NO).
HOx budget in continental boundary layer
kHOx=L(HOx)/HOx