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Measuring UV Measuring UV aerosol absorptionaerosol absorption
Why is aerosol UV absorption important ?
Change in boundary layer ozone mixing ratios as a result of direct aerosol forcing
+ 10%-20%
Aerosol “dimming” effects on UV trends may enhance reduce, or reverse effects of stratospheric O3 change
Satellite (TOMS/OMI)
overestimation of surface UV irradiance
3) Aerosol effects on photochemical smog production: aerosol scattering increases photolysis rates; while aerosol absorption decreases it:
22
21
23+ 0 - 10%
What we need to measure: abs
or Single Scattering Albedo (SSA): abs=(1-SSA)ext
Since 2002, the NASA TOMS, USDA UVB, AERONET and Aura/OMI programs have shared equipment, personnel and analysis tools to quantify aerosol
UV absorption using a
combination of ground based radiation measurements and RT modeling
AEROSOL UV absorption retrievals: 2002 - 2007
Brewer spectrometer : ozone, SO2, NO2
UV Multifilter Rotating Shadowband Radiometer
AERONET CIMEL sun-sky radiometers
+
+
1) UV-MFRSR extinction AOT compares well with AERONET and Brewer measurements
AERONETCloud-screened
UVMFRSR
SSA retrieval
AERONET retrievals of size distribution (PSD) and effectiverefractive index (real) at 440nm
1-min Diffuse/Total relative measurement (3% error)
absolute radiometric calibration of sky measurements (5% error)
Imaginary refr index, k, n440
A-priori information
Fitting of absolute sky radiances in almucantar
SSA at 325nm, 332nm and 368nm SSA at 440nm, 670nm ,870nm, 1020nm
Mie calculations
PSD = const
n=n440
k
ext
T
ozone
2) MFRSR SSA measurements in UV complement AERONET almucantar SSA inversions (440nm – 870nm):
MFRSR:-high frequency measurements
-Low solar zenith angles-High precision (no absolute calibration necessary)
AE
RO
NE
T a
nd
MF
RS
R A
OT
368
Sin
gle
Sca
tter
ing
Alb
edo
(SS
A)
MFRSR: SSA368
AERONET SSA440
Figure 1, upper:
Correction for NO2
Cede, A. J. Herman, A. Ritcher, N. Krotkov, J. Burrows, Measurements of Nitrogen Dioxide Total Column Amounts at Goddard Space Flight Center Using a Brewer Spectrometer in Direct Sun Mode , JGR 2006
1. Single scattering albedo (= scattering /ext )
NO2 Amount
NO2 Amount
November 10 2003: a~0.1 and NO2~0.03
NO2 Amount
1. Single scattering albedo (= scattering /ext )November 10 2003: a~0.1 and NO2~0.03
NO2 AmountNO2 AmountNO2 Amount
November 10 2003: / ~ NO2/ a~ 0.2
versus a (no NO2 correction)
Decrease of with a
is due to uncorrected NO2 at LOW a
SSA Retrieval neglecting NO2
versus a (with NO2 correction)SSA retrieval correcting for NO2
versus a (325nm )SSA retrieval correcting for NO2
What is SSA spectral dependence in the UV and visible wavelengths ?
UV -MFRSR has been modified to add 440nm filter used by AERONET
Good agreement between AERONET SSA and UV/VIS MFRSR
Modified UV/VIS MFRSR compared well with AERONET SSA at 440nm
Small ext
SCOUT-03 field campaign in Thessaloniki, Greece , July 2006
Roof of the Physics Dept., of the Aristotle University of Thessaloniki.
Modified UV/VIS MFRSR compared well with AERONET SSA at 440nm
Modified UV/VIS MFRSR compared well with AERONET SSA at 440nm:
Modified UV/VIS MFRSR compared well with AERONET SSA at 440nm:
Modified UV/VIS MFRSR compared well with AERONET SSA at 440nm:
Spring AGU, May 2007 MILAGRO session
Volkamer and Barnard, MILAGRO JGR special issue in prep.
?
Qi et al., AGU Dec 2006
Models underpredict SOA
Volkamer et al., 2006
Pollution Impacts on Biological Surface UV Radiation
1pm local time
0
2
4
6
8
10
12
UV Index vitamin-D
clean
gas only
UV ssa = 0.9
UV ssa = 0.7
x-polluted
S. Madronich - Spring AGU 2007, Acapulco, Mexico
NO2 + h nm) NO + O(3P)
2
3
4
5
6
7
8
0.E+00 2.E-03 4.E-03 6.E-03 8.E-03 1.E-02
J, s-1
z,
km
clean
gas only
UV ssa = 0.9
UV ssa = 0.7
x-polluted
O3 + h nm) O(1D) + O2
2
3
4
5
6
7
8
0.E+00 1.E-05 2.E-05 3.E-05 4.E-05
J, s-1
z,
km
clean
gas only
UV ssa = 0.9
UV ssa = 0.7
x-polluted
Single scattering albedo of pollution aerosols may be considerably smaller at UV than visible wavelengths Secondary organic aerosols?
Increased optical depth and ssa at visible wavelengths Absorption at UV wavelengths Composition is largely unknown
Large effects on Biologically active UV at surface, calculation of UV Index Photolysis rates in PBL
A challenge for air quality models Urban O3 production is approx. proportional to JNO2 Secondary organic aerosols also produced by photochemistry Negative feedback locally? Increased export of pollutants from megacity to region
Aerosol effect on OMI SO2 retrievals
0
500
1000
1500
2000
2500
3000
3500
0.00 0.20 0.40 0.60 0.80 1.00
HE
IGH
T (M
)East AIRE filed experiment in NE China , April 2005 -
submitted to the JGR Aura Special Issue
Aircraft in-situ SO2 measurements (red) and aerosol scattering profile (blue)
Future work:
1. In order to fully characterize absorption properties of the atmosphere one has to measure both NO2 and aerosol extinction () and single scattering albedo ( ).
2. With these new measurements we aim to discriminate between black carbon (BC) and organic carbon (OC) in pollution and smoke aerosols.
3. Validation of satellite UV , SO2 and aerosol absorption products from OMI
END
Mean aerosol optical depth: 0.82Mean aerosol single scattering albedo: 0.90
END
2. Single scattering albedo ( = scattering /ext )
NO2 Amount
May 13 2004: / ~ NO2/ a~ 0.03
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