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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