Organic aerosol and its climate impact

Min Zhong and Myoseon JangSept. 24, 2013

Department of Environmental Engineering SciencesUniversity of Florida

2013 FL A&WMA Conference

Aerosol: Key to improve climate prediction

2Source: IPCC 2007

heating

cooling

Green House Gases, small uncertainty

Atmospheric aerosol, large uncertainty

3

Direct effect

Indirect effect

• scattering• absorbing

• modifying cloud properties

How aerosol affects climate

Why study aerosol light absorption?

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1 Only absorption causes heating

2 Only a few types of aerosol absorb light,BC, OC, and mineral dusts.

5

VOC Emissions

Oxidation Reactions

(OH, O3, NO3) Nucleation or Condensation

Secondary

Organic

Aerosol

Direct Emission

Primary

Organic

Aerosol

POA & SOA

Role of OC in climate forcing

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global OC budget (154 Tg/yr)

1. OC is 95 wt% of carbonaceous aerosol

Source: IPCC 2007

2. Climate effect of OC has been poorly understood

Current model assumption: OC has no light absorption (Maria et al. 2004 ; Hoyle et al. 2009)

Recent research: OC has light absorbing capacity, d-limonene SOA, POA (Bones et al. 2010; Laskin et al. 2010 )

Motivation: What is the role of OC in climate system?

Black carbonNon-absorbing aerosol POA

SOA

5%

22%

73%

BC POA SOA

Objectives

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MAC: mass absorption cross section (m2/g)

Light absorption property

Warming or cooling

POASOA

To quantify aerosol’s climate impact, light absorption parameter is required.

Light absorption measurement

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Principle of the method: Beer Lambert’s law

ln(I0/I) = bvV/A

filter

sample

detector

UV/Vis light

Integrating sphere

bv: absorption coefficient (m-1) V: the volume of air drawn through the filter during a given sampling time, A is the area of the sample spot, M: aerosol mass concentration, C=1.4845

MAC = bv /M

How to obtain mass absorption cross section(MAC) ?

ln(I0/I) =C bvV/A

SOA experiments

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• SOA generation SOA UV-Vis spectra recording

filter sample

UV/Vis light

RUV-IS

2 m3 Teflon ChamberNOx

O3

GC-FID

SMPS

VOCs, NOx Inorganic seed

UV lamppumpfilter holder

MAC of SOAs

d-limonene(DL)

α-pinene(AP)

Toluene(TOL)

280 330 380 430 480 530 5800

3

6

9

12

15

TOL SOADL SOAAP SOA

wavelength(nm)

ab

sorb

ance

(m

g-1)

λ = 350nm λ = 450nm0.0

0.2

0.4

0.6

0.8

1.0

toluene

d-limonene

α-pinene

MA

C (

m2/

g)

MAC of TOL is 10 times higher than DL and AP more double bond , higher light absorbing

Zhong and Jang, AE, 2011

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POA experiment

East West

52m3 52m3

TUVR TUVRT/RH T/RH

GC-MS OC/ECNOxO3

SMPS

RUV-IS

TEOM

FTIR

Wood smoke

Smoldering burning to reduce the formation of BC

Hickory wood

MAC of POA

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10lnC

1)( OCOCabs Abs

V

Ab

OC

OCabsOC M

bMAC )(

Increase in morning: chromophore formation in SOA or

POA

Decrease in afternoon: sunlight bleachZhong and Jang, ACPD, 2013

Radiative forcing of organic aerosol

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RF of SOA is -0.09 ~ -0.06 w/m2 (Hoyle et al. 2009)

“Aerosol optical properties of SOA were taken to be similar to POA” (Hoyle et al. 2009).

In Myhre et al. (2007), they assume POA optical properties are equal to sulfate…

SOA = POA = Sulfate ?

Optical parameters from Mie calculation

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1. Particle size distribution assume lognormal distribution, with count median diameter of 138nm, geometric standard of 2 nm (Kaul at el. 2012)

2. Complex refractive index

assume n=1.44 (measured by Kim and Paulson, 2013), same from 280nm to 900nm. k is from my measurement

,

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MACk

Mie code from: http://www.hiwater.org/, shared by Dr. Tami Bond

Extinction cross sectionAerosol asymmetry factorSingle scattering albedo

Optical parameters

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Extinction cross section

Aerosol asymmetry factor

Single scattering albedo

Extinction cross section: similar

Asym >0 scattering in the forward direction

SSA (SOA) > SSA(POA)

Mie code from: http://www.hiwater.org/

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First estimation of radiative impact simple radiative efficiency: watts/(cm3 aerosol)

Chylek, P. and Wong, 1995

1. SOA and sulfate are similar, cooling aerosol

2. POA is warming aerosol.

3. It should be cautious to replace with each other.

280 380 480 580 680 780-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

sulfate RH=0%

POA RH=0%

SOA RH=0%

wavelength (nm)

For

cin

g ef

f. (

wat

t/cm

3)

Radiative efficiency code from: http://www.hiwater.org/

SOA = Sulfate ≠POA

Conclusions

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MAC of toluene SOA was the highest compared with MAC values for α-pinene SOA and d-limonene SOA

MAC of POA increased in the morning and decreased in the afternoon due to the competition between chromophore formation and sunlight bleaching

SOA is a cooling aerosol, with negative radiative forcing similar to sulfate. POA is a warming aerosol, with positive net forcing

Acknowledgment

This work was supported by grants from the National Science Foundation (ATM-0852747) and the Alumni Scholarship from the University of Florida.

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Questions?

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Thank you