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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?
4
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
6
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
7
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
8
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
9
• 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
11
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
12
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
13
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
14
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
,
4
MACk
Mie code from: http://www.hiwater.org/, shared by Dr. Tami Bond
Extinction cross sectionAerosol asymmetry factorSingle scattering albedo
Optical parameters
15
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/
16
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
17
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.
18
Questions?
19
Thank you