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

12

34

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%

12

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