Climate Eﬀects of Black Carbon Aerosols · Zamin Kanji and Andr´e Welti Ulrike Lohmann (IACETH)...

Intro How well do models simulate BC? BC radiative effects BC effects on ice clouds Conclusions Extra

Climate Effects of Black Carbon Aerosols

Ulrike Lohmann

ETH Zurich

Institute for Atmospheric

and Climate Science

Acknowledgements:

Zamin Kanji and Andre Welti

Ulrike Lohmann (IACETH) BC climate effects ETH Zurich, June 24, 2014 1 / 16


Bond et al., JGR (2013)



(a)

(c)

(a) (b)

(d)(c)

Scattering aerosols

Aerosol-radiation interactions

Absorbing aerosols

CoolingThe atmospheric circulation and mixing processes spread the cooling regionally and in the vertical.

Aerosols scatter solar radiation. Less solar radiation reaches the surface, which leads to a localised cooling.

At the larger scale there is a net warming of the surface and atmosphere because the atmospheric circulation and mixing processes redistribute the thermal energy.

WarmingAerosols absorb solar radiation. This heats the aerosol layer but the surface, which receives less solar radiation, can cool locally.

IPCC, Fig. FAQ 7.2, (2013)



Vertical profiles of BC

Pres

sure

(hPa

)

1000

Pres

sure

(hPa

)

0.01 0.1 1 10 100 1000BC MMR (ng kg-1)

0.01 0.1 1 10 100 1000BC MMR (ng kg-1)

GMI GOCART

IMPACT INCA ECHAM5-HAM

SPRINTARS TM5

OsloCTM2 BCC CAM4-Oslo CAM5.1 HadGEM2

GISS-MATRIX GISS-modelE

600

200

1000

600

200

HIPPO-1 (Jan 2009)20ºS - 20ºN

HIPPO-1 (Jan 2009)60ºS - 20ºS

A-FORCE (Mar-Apr. 2009)26ºN - 38ºN

HIPPO-1 (Jan 2009)20ºN - 60ºN

Fig. 7.15 (IPCC, 2013)



Transport to the Arctic

Bourgeouis and Bey, JGR (2011)



Aerosol radiative forcing 1750-2010

ï��

��

��

RFar

i (W

m-2)

Sulphate

POA FFBB

SOA

Nitrate

Mineral

Total

BC FF

hatched: Aero-

Com II models

solid: AR5 esti-

mates

(IPCC, Fig. 7.18,

2013)



Heterogeneous freezing

Hoose and Mohler, ACP (2012)



Compilation of freezing data on soot




Ice nucleation active surface site (INAS) density




Frozen fraction of droplets containing BC

233 234 235 236 237 238 239 240 241 242 2430.0

0.2

0.4

0.6

0.8

1.0 100 nm 200 nm 400 nm

Froz

en fr

actio

n

Temperature (K)

Regal Black

233 234 235 236 237 238 239 240 241 242 2430.0

0.2

0.4

0.6

0.8

1.0 100 nm 200 nm 400 nm

Froz

en fr

actio

n

Temperature (K)

GFG spark generator

233 234 235 236 237 238 239 240 241 242 2430.0

0.2

0.4

0.6

0.8

1.0 100 nm 200 nm 400 nm

Froz

en F

ract

ion

Temperature (K)

Fullerene

233 234 235 236 237 238 239 240 241 242 2430.0

0.2

0.4

0.6

0.8

1.0 100 nm 200 nm 400 nm

Froz

en fr

actio

n

Temperature (K)

Cast Black

233 234 235 236 237 238 239 240 241 242 2430.0

0.2

0.4

0.6

0.8

1.0Cast Brown

200 nm 400 nm

Froz

en fr

actio

n

Temperature (K)

Courtesy Andre Welti and Zamin Kanji (ETHZ)



Conclusions

BC as ice nuclei:

! BC nucleates ice only at rather cold temperatures

! The studies testing BC as an ice nuclei obtain conflicting results

Climate effects of BC:

! The total climate forcing of BC is positive, but could be close to zero

if co-emitted species are considered as well

! The effect of BC on clouds seems to counteract its direct radiative

effect, but they are much more uncertain



BC-rich sources comprise 99% of

all BC emissions

! Top bar: direct forcing by

aerosol and most gases and

aerosol cryosphere forcing

! Middle bar: cloud effects

and nitrate

! Bottom bar: net climate

forcing by each emission

source



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Climate Eﬀects of Black Carbon Aerosols · Zamin Kanji and Andr´e Welti Ulrike Lohmann (IACETH)...

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