Modeling organic aerosol where are we going wrong
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MODELING ORGANIC AEROSOL: Where are we going wrong?. Colette L. Heald ([email protected]). Telluride Workshop on Organic Aerosol August 4, 2008. ORGANIC CARBON AEROSOL SOURCES. S econdary O rganic A erosol. Semi- Volatiles. Nucleation or ReversibleCondensation. P rimary

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Modeling organic aerosol where are we going wrong

MODELING ORGANIC AEROSOL: Where are we going wrong?

Colette L. Heald

([email protected])

Telluride Workshop on Organic Aerosol

August 4, 2008


Organic carbon aerosol sources

ORGANIC CARBON AEROSOL SOURCES

Secondary

Organic

Aerosol

Semi-

Volatiles

Nucleation or

ReversibleCondensation

Primary

Organic

Aerosol

Oxidation

by OH, O3, NO3

Monoterpenes

Sesquiterpenes

Aromatics

Isoprene

Direct

Emission

Fossil Fuel Biomass

Burning

BIOGENIC SOURCES

ANTHROPOGENIC SOURCES


Geos chem oc aerosol simulation

Empirical parameterization: 2-product model fit to smog chamber studies

VOC + Oxidant α1P1 + α2P2

k1 k2

Equilibrium Partitioning

Depends on T, [OC]

GEOS-Chem OC AEROSOL SIMULATION

SecondaryOrganicAerosol

Monoterpenes/Sesq: Chung and Seinfeld [2002]

Isoprene: Henze and Seinfeld [2006]

Aromatics: Henze and Seinfeld [2008]

SOA treated as hydrophilic, semi-volatile gases are soluble

PrimaryOrganicAerosol

Fossil Fuel: Cooke / Bond

Biofuel: Logan & Yevich

Biomass burning: Duncan / GFEDv2

50% hydrophobic, 50% hydrophillic


Geos chem oc aerosol sources

GEOS-Chem OC AEROSOL SOURCES

SOA: ~30 Tg/yr

Monot/Sesq: 12

Isoprene: 14

Aromatics: 4

SOA ~ 1/3 of global source

Semi-

Volatiles

Nucleation or

ReversibleCondensation

Oxidation

by OH, O3, NO3

POA: 69 Tg/yr

FF: 11

BF: 8

BB: 50

Monoterpenes

Sesquiterpenes

Aromatics

Isoprene

Direct

Emission

Fossil Fuel Biomass

Burning

[Park et al., 2003; Henze and Seinfeld, 2008]


Why model estimates of soa can differ even with the same framework

WHY MODEL ESTIMATES OF SOA CAN DIFFER EVEN WITH THE “SAME” FRAMEWORK

  • BVOC emission inventories (EFs, drivers, etc)

  • Aromatic emission inventories

  • Oxidants (related to NOx, CO, VOC levels)

  • Pre-existing seed (which aerosols? With which emissions?)

  • Reversible formation?

  • Solubility of SOA and precursor semi-volatiles

  • Meteorology, esp. precipitation, convection  aerosol lifetime

Model estimates of SOA can *easily* differ by a factor of 2.

Current models, SOA production: 19-55 Tg/yr.


An example of model range

AN EXAMPLE OF MODEL RANGE

Tsigaridis and Kanakidou [2003] showed a large range of simulated OC due to various assumptions about SOA scheme.


Organic carbon aerosol at the surface

ORGANIC CARBON AEROSOL: AT THE SURFACE

2004 NARSTO Assessment

Global measurements (surface 0.5-32 μgm-3)

[Zhang et al., 2007]

Organic carbon constitutes 10-70% of aerosol mass at surface.

ISSUE: Measurements do not differentiate POA and SOA

IMPORTANT: Always remember what measurements we are targeting (PM1 – PM2.5)


Comparisons at surface sites

COMPARISONS AT SURFACE SITES

IMPROVE (1998)

MODEL

Factor of 2 underestimate by GISS model apparent (note used OM:OC=1.3) but suggested due to emissions and/or grid scale

[Chung and Seinfeld, 2002]

OBS

Good agreement between GEOS-Chem and IMPROVE observations for OC aerosol concentrations in the US (once primary sources corrected)

[Park et al., 2003]

Problematic: Can always adjust uncertain primary sources to account for discrepancies…


Neaqs 2002 organic aerosol growth in anthropogenic plumes

NEAQS 2002: ORGANIC AEROSOL GROWTH IN ANTHROPOGENIC PLUMES

NE US: Urban

BVOC: ~ 0.5 ppb

NOx: ~ 10 ppb

Obs OC ~ 6 (0-20) µg/m3

fOC/aer: ~65%

“Anthropogenic” air masses show more aerosol growth than can be explained by the oxidation of aromatics.

[de Gouw et al., 2005]


Ace asia first oc aerosol measurements in the free troposphere spring 2001

Mean Observations

Mean Simulation

Observations

+

ACE-ASIA: FIRST OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE (Spring 2001)

Off of Japan: Marine/polluted

BVOC: low? NOx: high?

Obs OC ~ 4 (1-12) µg/m3

fOC/aer: ~50% (surface), ~80% (aloft)

[Mader et al., 2002]

[Huebert et al., 2003]

[Maria et al., 2003]

(only terpene SOA)

Concentrations of OC in the FT were under-predicted by a factor of 10-100

We conclude this is missing SOA

[Heald et al., 2005]


Ace asia why we thought it would be soa

ACE-ASIA: WHY WE THOUGHT IT WOULD BE SOA

BIOMASS BURNING?

No fires in Siberia

Agricultural fires in SE Asia will not

affect FT off of Japan

Typical primary aerosol profile

(surface source only)

Obs

Model

Scavenging

Production?

ANTHROPOGENIC?

Influence FT??

No correlation with a “pollution” tracer

No apparent underestimate of primary

sources and/or mechanism to loft

into FT


Torch 2003 box model simulations require large increases in partitioning to match obs

TORCH 2003: BOX MODEL SIMULATIONS REQUIRE LARGE INCREASES IN PARTITIONING TO MATCH OBS

Southern UK: rural/occasional London plumes (high T)

BVOC: medium? NOx: medium?

Obs OC ~ 4 (0-10) µg/m3

fOC/aer: ~46%

  • To get this agreement:

  • Add 0.7 µg/m3bkgd

  • Increase partitioning coefficients by factor of 500

[Johnson et al., 2006]

These authors previously found that they needed to increases partitioning by a factor of 5-80 with the MCM to match aromatic SOA formation at the EUPHORE chamber [Johnson et al., 2004; 2005].


Mcma 2003 underestimated asoa

MCMA 2003: UNDERESTIMATED ASOA

Mexico City: highly polluted

BVOC: low NOx: high

Obs OC ~ 20 (0-40) µg/m3

fOC/aer: ~70%

Excess SOA from first-generation AVOC oxidation

[Volkamer et al., 2006]


Several studies suggesting underestimate of soa

SEVERAL STUDIES SUGGESTING UNDERESTIMATE OF SOA

Global underestimate in SOA?

[Volkamer et al., 2006]


Itct 2k4 modest model underestimate

ITCT-2K4: MODEST MODEL UNDERESTIMATE

NE US: urban/rural mix

BVOC: < 1 ppb NOx: medium

Obs OC ~ 1.5 (0-10) µg/m3

fOC/aer: ~43%

Sulfur Oxides (SOx)

Water soluble

OC Aerosol (WSOC)

Simulated source

attribution

Observed

Simulated

(includes isoprene SOA)

While model underestimated only by ~25% we cannot simulate variability in observations (R=0.21)

 incomplete understanding of formation.

[Heald et al., 2006]

Note: biomass burning plumes were removed


Milagro 2006 evolution of urban plumes

MILAGRO 2006: EVOLUTION OF URBAN PLUMES

NW US: Mexico (aircraft)

BVOC: low NOx: high

Obs OC ~ 5 (0-30) µg/m3

fOC/aer: ~60%

CAM-Chem simulation including

aromatic SOA [Heald et al., 2008]

for MILAGRO

Model

Obs

SOA/OC

Simulating increasing SOA fraction!

Jean-Francois Lamarque, in prep.

[Kleinman et al., 2008]


Impex asian plume transport

IMPEX: ASIAN PLUME TRANSPORT

NW US: Asian plume

BVOC: low NOx: low

Obs OC ~ 0.5 (0-5) µg/m3

fOC/aer: ~20%

Asian Pollution Layers

First OC overestimate by model!

How does this view match with the outflow from Asia (ACE-Asia)?

[Dunlea et al., submitted]


Amaze 08 oc aerosol in pristine conditions

AMAZE-08: OC AEROSOL IN “PRISTINE” CONDITIONS

Near Manaus, Brazil: clean tropical

BVOC: ~5 ppb NOx: 1-2 ppb

Obs OC: ~ 1 (0-4) µg/m3

fOC/aer: ~80%

Early Feb: observe significantly more organic aerosol than simulated (rain ends this period)

 Likely fire influence (either local of African)

Model does not significantly underestimate observed concentrations.

Observed OC is pretty low!

Preliminary AMS obs: Scot Martin, Qi Zhang (Harvard), Jose Jimenez, Delphine Farmer (CU Boulder)


Adding to our picture

ADDING TO OUR PICTURE…

  • Must break down at point where

  • signatures diluted/removed

AMAZE-08

ITCT-2K4

IMPEX

MILAGRO

Model underestimates not tracking photochemical age in all environments. What can we learn about SOA?

This does NOT mean that models are getting better!


Likely model weaknesses

LIKELY(?) MODEL WEAKNESSES

1. Current Emissions

2. Missing Precursors? Including semi-volatiles

3. Application of SOA yields  not relevant to ambient? Not including important drivers?

4. Partitioning: T-dependence, amount of pre-existing aerosol mass

5. Fate of gas-phase intermediates?

6. OC aging?

7. Additional formation pathways? (aqueous)

8. The effects of mixing state

9. Improperly characterized solubility, thus, loss


Sensitivity of soa concentrations to pre existing poa availability

SENSITIVITY OF SOA CONCENTRATIONS TO PRE-EXISTING POA AVAILABILITY

Is SOA formation limited by availability of POA?

YES

NO

Important effect on spatial distribution and amount of SOA formed

[Park et al., 2006]


Implications of new lab yields for pinene o 3

IMPLICATIONS OF NEW LAB YIELDS FOR α-PINENE+O3

GEOS-Chem Simulation: Surface JJA SOA from α-pinene+O3

Yield: Griffin et al., 1999

Yield: Shilling et al., 2008

Shilling - Griffin

Global annual mean burden of SOA from monoterpenes (when this yield applied for all) almost doubles from 0.28 TgC to 0.48 TgC


Missing source primary biological aerosol particles pbap

MISSING SOURCE:PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)

ALGAE

VIRUSES

BACTERIA

POLLEN

FUNGUS

PLANT

DEBRIS

Jaenicke [2005] suggests may be as large a source as dust/sea salt (1000s Tg/yr)

Elbert et al. [2007] suggest emission of fungal spores ~ 50 Tg/yr

How much does this source contribute to sub-micron OC?


Missing model source terrestrial primary biological aerosol particles pbap

MISSING MODEL SOURCE: TERRESTRIALPRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)

ALGAE

VIRUSES

BACTERIA

POLLEN

FUNGUS

From Andi Andreae (unpublished data)

LARGE particles (> 10 µm)

PLANT

DEBRIS

If we size-segregate the Elbert et al. [2007] estimate of emissions of PBAP, only 2 Tg/yr source of PM1 (total was 50 Tg/yr)

Also note, no initial suggestion from AMAZE-08 data that there is a large sub-micron PBAP source in the Amazon ([OC] ~ 1 µg/m3)

BUT some data suggests up to 40% of sub-micron OC is cellular…


Marine pbap

MARINE PBAP

Empirical marine PBAP source

(GEOS-Chem)

Mace Head

Obs

Chl-a

Mod

A source of 8 Tg/yr marine PBAP improves agreement with marine OC obs. Marine PBAP has limited influence on continental OC concentrations.

[Spracklen et al., 2008]

Other parameterizations for fraction of sea-spray that is organic.

More from Maria Kanakidou…

[O’Dowd et al., 2008]


Aqueous soa formation

AQUEOUS SOA FORMATION

SOA source:

2.6 TgC/yr

8.0 TgC/yr

  • Comprising:

  • Aqueous oxidation

  •  organic acids

  • 2. Oligomerization

Irreversible (?)

Uptake ~10-3

Glyoxal (45 Tg/yr)

Methylglyoxal (145 Tg/yr)

oxidation

VOCs

(esp isoprene)

[Fu et al., in press JGR]

An in situ SOA source with both biogenic and anthropogenic sources


Once we include all sources will simplified models be able to accurately simulate oc

ONCE WE INCLUDE ALL SOURCES, WILL SIMPLIFIED MODELS BE ABLE TO ACCURATELY SIMULATE OC?

Secondary

Organic

Aerosol

Cloud

Processing

Semi-

Volatiles

Nucleation or

ReversibleCondensation

Primary

Organic

Aerosol

Oxidation

by OH, O3,

NO3

Monoterpenes

Sesquiterpenes

Aromatics

Isoprene

Direct

Emission

Fossil Fuel Biomass

Burning


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