new insights in isoprene photooxidation: from chamber studies to...

Chamber studies GEOS-Chem

New insights in isoprene photooxidation:from chamber studies to global model

Fabien Paulot

Environmental Science & EngineeringCaltech

Fabien Paulot (ESE Caltech) Isoprene photooxidation 1 / 10


Introduction

Five carbons, two double bonds, thousands of papers and yet ...

Emissions : bottom-up and top-down inventories but the biologicalmechanism remains uncertain

Chemical mechanism :

: problems with organic nitrates, small carboxylic acidformation ...Low NOx: very poor understanding due to experimentalchallengesAerosol: what are the gas-phase precursors ofisoprene-originating aerosols

Climate change : CO2 vs Temperature influence



Introduction




High NOx : problems with organic nitrates, smallcarboxylic acid formation ...Low NOx: very poor understanding due to experimentalchallengesAerosol: what are the gas-phase precursors ofisoprene-originating aerosols




Introduction




High NOx : problems with organic nitrates, smallcarboxylic acid formation ...Low NOx: very poor understanding due to experimentalchallengesAerosol: what are the gas-phase precursors ofisoprene-originating aerosols


Unfortunately, everything is intermingled: isoprene still accounts for a verylarge fraction of the uncertainty in atmospheric chemistry(past-present-future)



Introduction




High NOx: problems with organic nitrates, smallcarboxylic acid formation ...Low NOx: very poor understanding due to experimentalchallengesAerosol: what are the gas-phase precursors ofisoprene-originating aerosols




Outline

1 Chamber studies

2 GEOS-Chem



Framework

Crounse et al. 2006, Paulot et al. 2009Fabien Paulot (ESE Caltech) Isoprene photooxidation 4 / 10


Advantages

Fast and direct measurements of a wide range of VOC (organicnitrates, small carboxylic acids, organic peroxides)Measurement of inorganic species: HONO, HO2NO2, H2O2, HNO3,N2O5 (indirect) → strong constraints to derive a mechanism

Time (min)

Sig

nal/c

ref

101

102

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5ISOPN (1,2) s: 0.84ISOPN (2,1) s: 0.85ISOPN (3,4) s: 0.83ISOPN (4,3) s: 0.84ISOPN (1,4)Z s: 1ISOPN (1,4)E s: 1ISOPN (4,1)Z s: 0.97ISOPN (4,1)E s: 0.95

0 0.5 10

2

4

6

8

10

12

Fraction of isopreneconsumed

App

aren

t α (

%)

Figure: Isoprene nitrate

.



Major conclusions

δ hydroxy channel

HO O

nd O o

n n i

O

o n k d

n h d O h o n d

NO 2

h o

n i

h O o h

D

d

?

o

i

h h o

OH

OH

O

O

O

HO

HO

O

HO O

O

HO

HO

O O

OH

HO

HO

O

O

HO

O

O

O HO

OH

O

O

OH

O

O

OH

O

O

OH O

O

O

O HO

O

O

O

O

O

O O N

HO

O

OH

O

OH

OH

O

O O

O

O

O

O OH

HO

OH

O

O OH

O

O O

H H

h o

h O

o n

n

O

h Oh o

OH

O

O

OH

O

O

OH

O

OH O

O

O O O OH

O

O HO O O

OH

OH

O

O

OH

O

O

O

O

n O

HC5 Z(4,1)

HACET

HC5 E(4,1)

HACET

MOBA Z(4,1) MPDL

GLYX

O O O

H

H D

ISOPN E(4,1) ISOPN Z(4,1)

DHMOB (4,1)

O

OH

O OH

1

23

4

OBLh o

n i

d k

i n

O

n k do

d h n o O

1

2 3

4

n

MOBA Z(1,4)

DHMOB

HMPL

MHBL

DHPN

HOPL

HOBL

HC5 Z(1,4)

GLYC

GLYC

PAN (m/z=250)

MPDL

MGLYX

MBDL

ISOPN (1,4)E ISOPN (1,4)Z

OBL

n i

h o n d

d

o n o d

n

O

k

n k do

O

1

2 3

4

*

OH

O

*

*

*

E 1-4 Z 1-4 Z 4-1E 4-1

1 2

3

4

O

O OH

O OH O

O

OH

O

O OH

O

O

O

OH

O O

OH

O

MACRMVK

1,4

1,2

2,1 3,4

4,3

4,1

41%

15%

23%

14 %

2.0 % 5.0 %

h

O

ISOPN (1,2) ISOPN (2,1) ISOPN (3,4) ISOPN (4,3)

o

OH OH

OH

OH

O

OH HO

OH

OH

OH

OH

HO

OH

OH

O

OH HO

o

O O

ho

o

15% 85 %

3-MF

?Surface Surface?

65% 35% 70%

30%

65% 35%

95% 5%

65% 35%

30%

70%

65% 35%

a

b

43% 28%

25.5%3.5%

43%28%

25.5%3.5%

15% 85 %

6.7%6.7%6.7% 6.7%

24% 24% 24% 24%

Isoprene nitrates

Overall yield: 12± 3%Large discrepancy between the β (∼ 6.7%) and δ hydroxychannels(∼ 24%)Short-lived (δ-hydroxy isoprene nitrates) with substantial recycling ofNOx: need to be included in the mechanismOther nitrates may have a significant role

MVK and MACR nitrates are formed with yields exceeding 10%MVK nitrate and propanone nitrate (∼ 1%) are very long-lived

Large formation of small carboxylic acid

Glycolaldehyde and hydroxyacetone (Butkovskaya 2006)Isoprene nitrates



Major conclusions

δ hydroxy channelConstraints on ∼ 30% of the carbonFormation of large acids

Isoprene nitrates

Overall yield: 12± 3%Large discrepancy between the β (∼ 6.7%) and δ hydroxychannels(∼ 24%)Short-lived (δ-hydroxy isoprene nitrates) with substantial recycling ofNOx: need to be included in the mechanismOther nitrates may have a significant role






Major conclusions


Isoprene nitratesOverall yield: 12± 3%Large discrepancy between the β (∼ 6.7%) and δ hydroxychannels(∼ 24%)Short-lived (δ-hydroxy isoprene nitrates) with substantial recycling ofNOx: need to be included in the mechanism

Other nitrates may have a significant roleMVK and MACR nitrates are formed with yields exceeding 10%MVK nitrate and propanone nitrate (∼ 1%) are very long-lived





Major conclusions


Isoprene nitratesOverall yield: 12± 3%Large discrepancy between the β (∼ 6.7%) and δ hydroxychannels(∼ 24%)Short-lived (δ-hydroxy isoprene nitrates) with substantial recycling ofNOx: need to be included in the mechanismOther nitrates may have a significant role






Major conclusions

Time (min)

ppb

101

102

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1ISOPN (4,1)ISOPN (2,1)Other sources



Major conclusions


Isoprene nitratesOverall yield: 12± 3%Large discrepancy between the β (∼ 6.7%) and δ hydroxychannels(∼ 24%)Short-lived (δ-hydroxy isoprene nitrates) with substantial recycling ofNOx: need to be included in the mechanismOther nitrates may have a significant role






Major conclusions

Time (min)

ppb

100

101

102

0

1

2

3

4

5

6

7

8

9

10

GLYCHACETMVKNHMHPISOPN (1,4)3−MFHC5 Z41Other sources

0 200 400 6000

5

10

15



Outline

1 Chamber studies

2 GEOS-Chem



0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55

180° W 135° W 90° W 45° W 0° 45° E 90° E 135° E

90° S

60° S

30° S

0°

30° N

60° N

Summer NH Isoprene nitrate



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

180° W 135° W 90° W 45° W 0° 45° E 90° E 135° E

90° S

60° S

30° S

0°

30° N

60° N

Formic acid Northern Hemisphere summer



Work in progress and acknowledgements

Low NOx chemistry: isoprene (Paulot et al. in review) andatmospheric relevant products: MVK, MACR, MBO, ... (Crounse etal. in preparation)

Fate of the peroxidesOH recycling

Current chemical schemes are very wrong over tropical regions(not specific to GEOS-Chem).

Compare model with CIMS measurements collected during INTEX-B,TC4 and ARCTAS.



Work in progress and acknowledgements

Low NOx chemistry: isoprene (Paulot et al. in review) andatmospheric relevant products: MVK, MACR, MBO, ... (Crounse etal. in preparation)

Fate of the peroxidesOH recycling

Current chemical schemes are very wrong over tropical regions(not specific to GEOS-Chem).

Compare model with CIMS measurements collected during INTEX-B,TC4 and ARCTAS.

John D. Crounse, Henrik G. Kjaergaard (University of Otago, NewZealand), Jesse H. Kroll (now at MIT), John H. Seinfeld, Paul O.

Wennberg

NSF, NASA, EPA, Davidow Fellowship, Davidow Fund


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