2013 FL A&WMA Conference
Min Zhong and Myoseon Jang
Sept. 24, 2013
Department of Environmental Engineering Sciences
University of Florida

Aerosol: Key to improve climate prediction cooling heating
Green House Gases, small uncertainty
Atmospheric aerosol, large uncertainty

• scattering
• absorbing
• modifying cloud properties
3

1 Only absorption causes heating
2
Only a few types of aerosol absorb light,
BC, OC , and mineral dusts.
4

POA & SOA
Direct
Emission
P rimary
O rganic
A erosol
VOC
Emissions
Oxidation
Reactions
(OH, O
3
, NO
3
)
Nucleation or
Condensation
S econdary
O rganic
A erosol
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Role of OC in climate forcing
5%
22%
1. OC is 95 wt% of carbonaceous aerosol
73%
BC POA SOA global OC budget (154 Tg/yr)
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 )
SOA
Non-absorbing aerosol POA Black carbon
Motivation: What is the role of OC in climate system?
6

Objectives
To quantify aerosol’s climate impact, light absorption parameter is required.
MAC: mass absorption cross section (m 2 /g)
Light absorption property
SOA
Warming or cooling
POA
7

Integrating sphere
Principle of the method: Beer Lambert’s law ln(I
0
/I) = b v
V/A detector filter sample ln(I
0
/I) = C b v
V/A
UV/Vis light
How to obtain mass absorption cross section(MAC) ?
MAC = b v
/M b v
: 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
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•
SOA generation  SOA UV-Vis spectra recording
NO x
O
3
UV lamp
2 m 3 Teflon Chamber
GC-FID filter holder pump
UV/Vis light
SMPS filter sample
VOCs, NO x
Inorganic seed
RUV-IS
9

15
Toluene
(TOL)
12
9
6
MAC of SOAs d -limonene
(DL)
α -pinene
(AP)
1,0
TOL SOA
DL SOA
AP SOA
0,8
0,6 toluene d-limonene
α-pinene
0,4
3
0,2
0
280 330 380 430 480 530 580 wavelength(nm)
0,0
λ = 350nm λ = 450nm
 MAC of TOL is 10 times higher than DL and AP
 more double bond , higher light absorbing
Zhong and Jang, AE, 2011

East
52m 3
West
52m 3
TUVR
T/RH
TUVR T/RH
Wood smoke
O
3
SMPS
FTIR
NO x
GC-MS
TEOM
RUV-IS
OC/EC
Hickory wood
Smoldering burning to reduce the formation of BC
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b abs ( OC )

1 A
Abs
OC ln
C V
MAC
OC
 b abs ( OC )
M
OC
 Increase in morning : chromophore formation in SOA or POA
 Decrease in afternoon : sunlight bleach
Zhong and Jang, ACPD, 2013 12


RF of SOA is -0.09 ~ -0.06 w/m 2 (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 ?
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Extinction cross section Aerosol asymmetry factor Single scattering albedo
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 k

MAC
 
4

,
Mie code from: http://www.hiwater.org/ , shared by Dr. Tami Bond
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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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 simple radiative efficiency: watts/(cm 3 aerosol)
2
Chylek, P. and Wong, 1995
1,5
1
0,5
0
-0,5
-1
-1,5
-2
280 380 sulfate RH=0%
POA RH=0%
SOA RH=0%
480 580 wavelength (nm)
680 780
1. SOA and sulfate are similar, cooling aerosol
2. POA is warming aerosol.
3. It should be cautious to replace with each other.
SOA = Sulfate ≠ POA
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Radiative efficiency code from: http://www.hiwater.org/

 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
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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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