Investigating the Effects of Atmospheric Aging on the Radiative

Investigating the effects of atmospheric aging on the direct radiative properties and

climate impacts of black‐ and brown‐ carbon aerosol

Jesse H. Kroll, Colette L. Heald

Department of Civil and Environmental Engineering, MIT

Paul Davidovits, Andrew T. Lambe

Department of Chemistry, Boston College

14 November 2014

BC climate forcing: Large, complex, uncertain

[Bond et al., 2013]

       Simple lifecycle of atmospheric BC

optical properties

transport

emission deposition

       Simple lifecycle of atmospheric BC

optical properties

transport aging

emission deposition

This project

Black/brown carbon aerosol is chemically dynamic, subject to atmospheric aging reactions; these can lead to dramatic changes in physicochemical properties, and therefore climate forcing effects.

A complete understanding of this aging, and representation of this aging within models, is necessary for the accurate simulation of global direct radiative forcing.

Key BC aging reactions

+1) Coagulation

ox + SO2 H2SO4 (or (NH4)2SO4) coating

(NH3)

ox + NO22) Condensation NH4NO3 coating

NH3

+ VOC ox

SOA coating

ox3) Heterogeneous + OH/O3 surface oxidation oxidation

Effects of aging on BC properties

1) Enhancement of light absorption by coatings (“lensing effect”) [e.g., Schnaitner 2005, Bond et al. 2006, Schwarz et al. 2008, Lack et al. 2009, Cappa et al. 2012]

+ VOC ox

“darker”

2) Increased water‐uptake ability by coated or oxidized BC

+ H2O

Higher hygroscopicity can lead to …

‐more efficient light scattering (due to larger particles from water uptake) ‐ shorter atmospheric lifetimes due to increased wet deposition

(‐more facile activation to form cloud droplets)

       Simple lifecycle of atmospheric BC

optical optical properties properties

emission deposition

transport aging

Simple lifecycle of atmospheric BrC

“Brown carbon”: OC that absorbs in the UV/visible (distinct molecules)

? SOA aging

“browner”

formation

?

emission deposition

BrC

“whiter”

This project

Black/brown carbon aerosol is chemically dynamic, subject to atmospheric aging reactions; these can lead to dramatic changes in physicochemical properties, and therefore climate forcing effects.

A complete understanding of this aging, and representation of this aging within models, is necessary for the accurate simulation of global direct radiative forcing.

Major questions: ‐ what are the most important atmospheric aging transformations of BC/BrC?

‐ what effects do aging reactions have on climate‐relevant properties of BC/BrC?

‐ how do these aging reactions impact BC/BrC direct radiative forcing?

Approach: Laboratory + Modeling

Development of global modeling framework for representation of aging, climate effects �

calculation of DRF

Laboratory studies of BC/BrC aging reactions: Changes to chemical + optical properties

IPCC AR5 Estimates that Black Carbon is the 2nd Largest Warming Agent in the Atmosphere.

(but that’s not what models say)

IPCC AR5

Bond et al., 2013 How can these be reconciled?

ACCMIP (Shindell et al., 2013)

IPCC AR4

AeroCom II (Myhre et al., 2013)

BC (FF/BF)

BC (BB)

0 0.2 0.4 0.6 0.8

TOA DRF (Wm‐2)

Observations Also Suggest That Models Overestimate BC

AeroCom means in black, HIPPO obs in colour Obs in black, AeroCom models in colour [Schwarz et al., 2010] [Koch et al., 2009]

AeroCom models overestimate BC over Americas & remote Pacific by factor ~5‐8.

Aging Processes may Reconcile Both Mass and Absorption Constraints

AbsorpƟon ↑ LifeƟme ↓

Aging GEOS‐Chem integrated with RRTMG (GC‐RT) (Heald et al., 2014)

+ Emission Absorption (AERONET) Mass Concentrations (ARCTAS,

EUCAARI, HIPPO + surface)

New Model Aging Processes for BC

Hydro‐phobic

Hydro‐philic

Old Assumptions

1.15 days

Hydro‐phobic

Hydro‐phobic

New Assumptions

Anthropogenic

Biomass burning

Hydro‐philic

Hydro‐philic

Sulfate, etc.

Organic components

4 hours (also increase fraction emitted as

hydrophillic to 70%)

k = 1/τ = a [SO2] [OH] + b

Based on several lab and field studies, esp Liu et al. (2010); Akage et al. (2012)

Good simulation near source (with or without new aging).Modified aging scheme results in shorter lifetime and better 

simulation of low concentrations in remote locations. Vastly better than AeroCom. Generally within a factor of 2. 

Impact of New Model Aging Processes on Simulation of BC

HIPPO Continental (Near‐Source)

Good

Better

Still Bad

Considering Absorption Enhancement of BC

Anth BC

BB BC

Smaller size, wider size range

Mie calculation

Larger size, narrower size range

Mie calculation

Absorption Coefficient

Absorption Coefficient

Absorption enhancement from coating (AE=1.1)

Absorption enhancement from coating (AE=1.5)

Also “Most Absorbing” Simulation : Set AE=2 and standard aging mechanism (longer lifetime)

(Akage et al., 2012; Schwarz et al., 2006; 2007; 2008; Lack et al., 2012; Dubovik et al., 2002; Shamjad et al., 2012; Moffet et al., 2009; Knox et al., 2009; Kondo et al., 2011; Lack et al., 2012; Moffet and Prather, 2009; Bond et al., 2006; Cappa et al.,

2012)

Adding Brown Carbon to GEOS‐Chem

Aromatic SOA

Brown Carbon

Get RI from field measurements Absorption

Mie calculation Coefficient 50% of biofuel POA 25% of fire POA

MAE=1 m2/g MAE=0.3 m2/g

Absorption of BrC is highly uncertain ‐ we choose upper‐range estimates

Including Brown Carbon is Critical to Capturing the Spectral Dependence of AERONET AAOD

*AAOD product here using lev2 SSA with lev1.5 AOD

Measurements Still Suggest Absorption is Underestimated

Better able to capture the spectral AAOD with our “best” simulation (including BrC), but still biased low (especially in some biomass burning regions).

Can “scale up” our model to match observations (Bond et al., 2013) – emissions or optics?

*AAOD product here using lev2 SSA with lev1.5 AOD

Our Work Suggests Smaller BC DRF Required to Match All Observational Constraints

Scaled GCRT

BC (FF/BF)

BC (BB)

BrC

"Best" GCRT

Standard GCRT

IPCC AR5

Bond et al., 2013

ACCMIP (Shindell et al., 2013)

IPCC AR4

AeroCom II (Myhre et al., 2013)

0 0.2 0.4 0.6 0.8

TOA DRF (Wm‐2)

Brown Carbon contributes 35% of the warming from carbonaceous aerosols. BC DRF is less than methane and tropospheric ozone.

Suggests that controlling BC is less effective for climate mitigation.

[Wang, et al., ACP, 2014]

Lab Study 1: Heteogeneous oxidation of BC

with Kevin Wilson (LBNL), Manjula Canagartna and Paola Massoli (ARI)

AtomizerN2

Pump

T

O2

Drier

SP-AMS

BC source

[Browne, et al., submitted]

SP‐AMS with VUV ionization

VUV (12 eV photons)

Soot‐Particle Aerosol Mass Spectrometer: Real‐time measurement of mass, composition of particles (OC, BC, inorganics)

Ionization efficiencies PAHs: 7‐8 eV Most organics: 9‐10 eV BC fragments (e.g. C3): ~11.5 eV

[Onasch et al. 2012]

Heterogeneous aging: BC “cores” unaffected

300 C x/20 (Hz)3 SMPS Integrated volume (ug/m )250

Cx accounts for the majority200

of the flame soot mass 150

100

12:00 AM 2:00 AM 4:00 AM2/2/2013

0.5

Frac

tion

of C

x spectrum remainsCCx

0.4 C 2 constant with aging: C 3 BC “core” is inert on the0.3 C 4 timescale of atmospheric agingC5 - C100.2

0.1

120.0 0.5 1.0 1.5 2.0x10-3OH exposure (molecules cm s)

Changes to adsorbed organic species N

orm

aliz

ed to

Cx

0.16

0.12

0.08

0.04

0.00

80x10

CH CHO CHO>1

no oxidation

20 40 60 80 100 120

-3

60

40

20

0

~2 days oxidation

20 40 60 80 100 120

Organics associated with BC (representing small fraction of total particles) undergo dramatic chemical changes

Continual changes with oxidant exposure

Approximate days0.0 0.5 1.0 1.5 2.0 2.5

1.2

Sig

nal n

orm

aliz

ed to

Cx

1.0

0.8

0.6

0.4

0.2

0.0

250x109200150100500 OH exposure (molecules s cm

-3 )

Reactant CxHy +

CxHyO+

CxHyOz +

Rapid loss of organic species

[Org

]/[O

rg] 0

1.0

0.8

0.6

0.4

0.2

0.0

0 5 10 15 20 Approximate days of OH exposure

Lifetime of adsorbed organics is short

Follow‐up experiments: Water uptake (hydrophobic hydrophilic)

m/z 202 m/z 216

Loss of adsorbed PAHs

[PAH

]/[PA

H] 0

1.0

0.8

0.6

0.4

0.2

0.0

m/z 202: pyrene

m/z 216: benzo[a]fluorene

0 5 10 15 20 Approximate days of OH exposure

Long‐timescale “survival” of PAHs (morphology)

Next: Coating + heterogeneous ox. experiments

Flow tube reactor

soot particle generation

reagent/oxidant preparation

analytical instrumentation

SPMS (size) CPMA (mass)

SP‐AMS (composition)

EAD (surface area) CAPS‐SSA, CRD‐PAS

(absorption, scattering)

March 2015

        )  

Experimental matrix

BC source ‐ fractal soot from McKenna burner (denuded at 300oC) ‐ also atomized black carbon spheres

Particle size ‐monodisperse, 30‐300 nm

Aging type ‐ OH + SO2 (sulfuric acid coating, het. ox) ‐ OH + NH3 + SO2 (ammonium sulfate coating, het. ox) ‐ OH/O3 + VOCs (SOA coating, het. ox ‐mixed coatings

Parameterization

Changes to composition/hygroscopicity + optics as a function of atmospheric exposure (to match representation in Wang et al. 2014)

Key optical parameters determined, included in a “lookup table” (or interpolated function) based on experimental results

particle size mass extinction efficiency

relative humidity single scattering albedo

wavelength asymmetry parameter

mixing state (BC:org:SO4)

Summary/conclusions

‐Modeling vs measurements of BC: models overestimate loadings, underestimate aerosol absorption

‐ Aging processes can affect both concentrations (via changes to deposition) and optical properties (via changes to coatings); need for an improved understanding, description of such processes

‐ Global modeling results: Improved agreement between predicted, measured BC loadings and properties (but AAOD still underestimated!)

‐ Laboratory results: Heterogeneous oxidation an efficient way to change organic components of soot; oxidation can dramatically decrease“brown”‐ness of brown carbon

‐ Next step: Laboratory results implementation in models

Acknowledgements

Manjula Canagaratna Kevin Wilson Eleanor Browne Andrew Lambe Paola Massoli Thomas Kirchstetter Xuan Wang Paul Davidovits Timothy Onasch Jonathan Franklin Douglas Worsnop Kelsey Boulanger

David Ridley

Xiaolu Zhang Christopher Cappa

Joshua Schwarz Anne Perring Ryan Spackman

Dantong Liu Hugh Coe

Anthony Clarke

Publications from this Project: Heald et al., ACP, 2014 Wang et al., ACP, 2014 Browne et al., JPCA, submitted Lambe et al., ES&T, 2013

RD83503301