A self-generating approach for explicit mechanisms

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A self-generating approach for explicit mechanisms. B. Aumont, M. Camredon, J. Lee-Taylor, S. Madronich. International Conference on atmospheric chemical ...
International Conference on atmospheric chemical mechanisms

A self-generating approach for explicit mechanisms B. Aumont, M. Camredon, J. Lee-Taylor, S. Madronich

December 6-8, 2006

Why should we develop explicit organic chemical schemes ? VOC oxidation produces a large number of intermediates. These intermediates play a key role in the HOx and NOx budget and therefore in the tropospheric O3 formation. Secondary VOC are usually multifunctional species, i.e. having high water solubility and/or low vapor pressure. These organic intermediates may : • modify the chemical and physical properties of aerosol by Secondary Organic Aerosols production • modify cloud chemistry (e.g. acid formation) and microphysics (e.g. surface tension effect, properties of aerosol acting as CCN…)

NO →NO2 conversion HOx sink NOx sink

Explicit scheme = reference scheme to test the relevance of simplified (reduced) schemes used in 3D models. Objective tools to explore our ignorance through comparisons with observations

From the parent species to the first generation

From the first to the second generation ONO2

NO →NO2 conversion HOx sink NOx sink

From the parent species to the first generation

NO →NO2 conversion HOx sink NOx sink

From the first to the second generation

How big are explicit chemical schemes ? 107 106

n-alkanes i-alkanes 1-alkenes Isoprene

f o r be m Nu

105

ac e r

ns o ti

of r be m Nu

104

A fully explicit description leads to schemes dealing with an exorbitant number of species

s

pe

s e i c

Two problems : Explicit schemes are too large to be reasonably written by hand

103 Aumont et al., ACP, 2005

102

3

4

5

6

7

8

The quantity of physical and chemical data needed to develop explicit schemes is far in excess of available experimental data.

Carbon number Data processing tools are required to: Assimilate all the data provided by laboratory studies Codify the various estimation methods Generate consistent and comprehensive multiphase oxidation schemes on a systematic basis

The chemical scheme generator µ What we expect from a generator : Automatic creation of fully-explicit schemes on the basis of a predefined protocol. starting point

CH3CH2CH3 CH3CH2CH3 CH3CH2CH(OO.) ………..

CH3CH(OO.)CH3 ……….. ………..

+ OH => CH3CH2CH(OO.) + H2O + OH => CH3CH(OO.)CH3 + H2O ……….. + NO => => ……….. ……….. + NO => => ……….. ending point => CO2 + H2O

k1 k2 … … … …

µ The protocol Define the set of rules that lay out the choice of reaction pathways (and their associated rate constant). 1- When available, kinetic data taken from laboratory measurements are assigned 2- Otherwise, an estimation of the rate constant, stoichiometric coefficients and reaction products is performed using structure/activity relationships.

The chemical scheme generator Generator = Expert system that - assimilates physical and chemical data from laboratory experiments - estimates the missing information based on structure/activity relationships

Input Hydrocarbons

Output Automatic generator for VOC oxidation scheme Machinery :

Laboratory data

Explicit chemical schemes

structure/activity relationships

The protocol currently used : - Conceptually similar to the MCM3 mechanism - Most SAR implemented were borrowed from SAPRC99, MCM and NCAR MM - Described in Aumont et al., ACP, 2005

Low diagram of the generator New reaction products added to the stack VOCn

VOC2 VOC1 Radical ?

no C-H ? OH reaction RH + OH → RO2 >C=C< + OH → >C(OH)C(O2)< O3 reaction >C=C< + O3 → >C=O + Criegee Criegee → products + OH NO3 reaction RCHO + NO3 → R(O)OO >C=C< + NO3 → >C(ONO2)C(O2)< Photolysis RCHO + hν → R + HCO RONO2 + hν → RO + NO2 ROOH + hν → RO + OH

>C=C< ?

RO2 ? Peroxy alkyl chemistry RO2+NO → RO+NO2 RO2+NO → RONO2 RO2+NO3 → RO+NO2+O2 RO2+HO2 → ROOH + O2 RO2+RO2 → products RCO3 ?

-CHO ?

>C=O ? -ONO2 ? -OOH ? -C(O)OONO2 ?

Thermal decomposition RCO(OONO2) → RCO(OO)+NO2

yes

Peroxy acyl chemistry RCO3+NO → R+CO2+NO2 RCO3+NO2 → RCO(OONO2) RCO3+NO3 → R+CO2+NO2+O2 RCO3+HO2 → RCO(OOH) + O2 RCO3+HO2 → RCO(OH) + O3 RCO3+RO2 → products RO ? Alcoxy chemistry >CH(O⋅)+O2 → >C=O + HO2 >CH(O⋅)C2C(O.)< → >C(O⋅) C2C(OH)< >C(O⋅)-R → >C=O + R

Treat next species in the stack

The chemical scheme generator

Input

Hydrocarbons

Set of rules for simplification Lumping protocol

Output

Automatic generator for VOC oxidation scheme Explicit chemical schemes

Laboratory data

Machinery : structure/activity relationships

Reduced (simplified) chemical schemes

Chemical scheme reduction (Near near) explicit scheme (~70 primary species) Reference scheme 359 660 species 2 270 159 reactions Reduced scheme ~150 species ~500 reactions

Starting scheme

Ending scheme Automatic & systematic reduction

Chemical scheme reduction (Near near) explicit scheme (~70 primary species)

Starting scheme Ending scheme Automatic & systematic reduction

Accuracy of the each reduction procedure can be quantified using the explicit scheme as a reference See Szopa et al., ACP, 2005

Explicit scheme as an « exploratory vehicle » to explore the behavior of organic matter during oxidation

- where does the carbon go ? -

Explicit modeling of octane oxidation Chemical scheme : 1.2×106 species 7.5×106 reactions Simulation conditions : T=298 K [octane]0 = 20 ppb [NOx]0 = 10 ppb

Mixing ration (ppbC)

Modeling VOC oxidation : where does the carbon go ? Total simulated carbon

150

Octane 100

total secondary organics

CO+CO2

50

0

0

2

4

6

8

Time (day)

10

12

How does organic reactivity evolve after the first oxidation steps ? - Contribution to HOx, NOx, Ox budget at regional to global scale ? - How does strong emission sources affect the continental and remote troposphere?

Mixing ratio (ppbC)

Modeling VOC oxidation : where does the carbon go ? Octane 100

Mixing ratio (ppbC)

Chain lengths of secondary organics

total 80

total secondary organics

0

2

4

6

10

12

Number of functional groups borne by C8 species

C8

C8

40

8

Time (day)

80

40

2 1 3

C1 to C7 0

CO+CO2

50

0 120

Total simulated carbon

150

4 0

2

4

6

8

Time (day)

10

12

00

2

4

6

8

Time (day)

10

12

Most secondary organics are water soluble. How does organic matter evolve during cloud events? What is the contribution of aqueous processes in: - The removal of VOC - Acids formation - Organic aerosols formation (after cloud evaporation) - The oxidant budget

2 functional groups : typical species

Number of functional groups borne by C8 species

80

40

O

O

C8

OH

O

ONO2

ONO2

2 1 3 4

OH

O

00

2

4

6

8

Time (day)

10

12

Some secondary organics are non-volatile species. What is the fraction of the parent compound that leads to aerosols ? What is the contribution of organic condensation to: - Hygroscopic behavior (CNN activation) - Size distribution - Optical properties

4 functional groups : typical species Number of functional groups borne by C8 species

80 O

O

O

O

ONO2 O O

O

ONO2

C8

O

OH ONO2 O

40

O

2 1 3 4

OH

OH

00

2

4

6

8

Time (day)

10

12

How far should we go in the description of VOC oxidation ? Number of functional groups borne by C8 species

Mixing ratio (ppbC)

80

C8

SGMM (explicit) MCM

2 40

1 3 0

0

2

4 4

6

Time (day)

8

10

12

How far should we go in the description of VOC oxidation ? Evolution of organic functionalities during octane oxidation

Ri/C =

Number of carbons bearing function i Total number of organic carbons

How far should we go in the description of VOC oxidation ? Evolution of organic functionalities during octane oxidation

Evolution of nitrogen compounds and ozone during octane oxidation

OZONE

Multiphase VOC oxidation : Development of a data processing tools to generate kinetic schemes and thermodynamic equilibrium (LISA/NCAR) gas HC + oxidant ox VOC Water soluble ox VOC semi-volatils

Many questions surround the role of multifunctional organics in the chemistry of multiphase system

The main difficulties : description of the sources and sinks of a myriad of VOC that may partition to condensed phases.

ox CO2 + H2O Kinetic module Gas phase generator

Method : extension of the self generating approach to model multiphase system

Multiphase VOC oxidation : Development of a data processing tools to generate kinetic schemes and thermodynamic equilibrium (LISA/NCAR) gas HC + oxidant ox VOC Water soluble ox

clouds VOC Water soluble Dynamical module – Gas/droplets mass transfert

VOC semi-volatils aerosols aérosols

ox

SVOC

CO2 + H2O Kinetic module Gas phase Thermo. Module Equilibrium gas/aerosols

VOC semi-volatils

Multiphase VOC oxidation : Development of a data processing tools to generate kinetic schemes and thermodynamic equilibrium (LISA/NCAR) Kinetic module Aqueous phase

gas HC + oxidant ox VOC Water soluble ox

clouds VOC Water soluble Dynamical module – Gas/droplets mass transfert

VOC semi-volatils

ox VOC semi-volatils

aerosols aérosols

ox

SVOC

CO2 + H2O

Polymerisation oxidation

Kinetic module Gas phase Thermo. Module Equilibrium gas/aerosols

non-volatil compounds Kinetic module Aerosol phases

Microphysical Module

Multiphase VOC oxidation : Development of a data processing tools to generate kinetic schemes and thermodynamic equilibrium (LISA/NCAR) Kinetic module Aqueous phase

gas HC + oxidant ox VOC hydrosoluble Water soluble ox

clouds COV hydrosolubles dynamical module – Gas/droplets mass transfert

VOC semi-volatils

ox COV semi-volatils

aerosols aérosols

ox

SVOC SVOC

CO2 + H2O

Polymerisation oxidation

Kinetic module Gas phase Thermo. Module Equilibrium gas/aerosols

non-volatil compounds Kinetic module Aerosol phases

Microphysical Module

Explicit modelling of the gas/particle partitioning

AEROSOL PHASE

GAS PHASE

oxidation

COV +ox

CONDENSATION: absorption COSVi

oxidation

COSVi +ox

CO+CO2

Raoult’s law : Pi = γi xi Pvap i Pvap are estimated for each intermediate using Myrdal & Yalkowski (97) structure/properties relationship (see Camredon et al., Atmos. Env., 2006)

Gradual change of organics during 1-octene oxidation Typical species ONO2

concentration (ppbC)

80

60

O

Total simulated carbon

octene Gaseous secondary organics

OH

OH

ONO2 OH

CO+CO2 O

OH

OH

20

Particulate secondary organics 0 3 4 2 1 0 temps (jours) Simulation conditions : T=298 K, [octene]0 = 10 ppb, [NOx]0 = 1 ppb (constant)

OH

ONO2

40

5

O

ONO2 O

OH

O

ONO2

OH

OH

OH

Evolution of organic functionalities during octene oxidation Gas phase

Aerosol phase

PAN -OH

-OH

-ONO2

-ONO2

-CHO -CO-

Ri/C =

-CO-

Number of carbons bearing function i Total number of organic carbons

ketone

carboxylic acid

PAN

peracid

nitrate

hydroperoxide

aldehyde

alcohol

Future developments … GAS PHASE

CONDENSE PHASE

oxidation

COV polymers

+ox

CONDENSATION: absorption COSVi

COSVi oxidation

polymerization oxidation +ox

+ox

CO+CO2

H2O H2O inorganic

COSVj inorganic

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