royal meteorological institute of belgium validation of the method to retrieve the aod and first...

Royal Meteorological Institute of Belgium

Validation of the method to retrieve the AOD and first preliminary results of the aerosol measurements campaign. RMI December 6 th 2006.

• Validation of the method to retrieve the Aerosol Optical Depth from the Brewer Ozone measurements

• First preliminary results of the aerosol measurements campaign at Uccle


Validation of the method to retrieve the AOD. RMI December 6th 2006.

Validation of the method to retrieve the Aerosol Optical

Depth from the Brewer Ozone measurements

Anne Cheymol, Hugo De Backer, Weine Josefsson and René Stübi

[email protected]

Cheymol et al., jgr, 2006



Overview1. Introduction

2. The Brewer spectrophotometer instrument

3. Description of the method

4. Results

Impact of the neutral density filter on AOD and Validation of the AOD between a Brewer and a sunphotometer

Comparisons between different Brewer at the same place

5. Conclusions and perspectives

Role of aerosol particles

• Most aerosol particles’s knowledge is in VIS and IR and not in UV

• Important role in climate forcing UV-B irradiance reduction by about 5-35% Indirect effect on clouds• Impact on Human health



Anthropogenic origin

Polluted day on January 28th 2006



Photo by A. Delcloo and A. Mangold

smoke

Clear day on November 9th 2006

Natural origin

Sea salt ejected from the sea in the air



Photo by Plisson

Natural origin



Clean roof

Photo from the web

Pollen

Seasonal cycle of AOD at Uccle








4. Results


Comparisons between Brewer at the same place



Validation of the method to retrieve the AOD. RMI December 6th 2006

Over 100 Brewer stations (blue points)



280-363 nm

306-320 nm



Zenith angle = za

sunset

Rotation of the instrument during the day

12H

AfternoonMorning


Summary of the Brewer measurements

• 5 Direct Sun measurements/3mns every 30mns

• Automatic rotation during the day to follow the sun

• No cloud direct sun measurement

• 25° za 70 ° for one day at Uccle




Aerosol Optical Depth = attenuation of solar radiation by aerosol particles

Direct Sun radiation at 306, 310, 313, 316 and 320 nm






4. Results




Attenuation of solar radiation




Beer’s law equation

S() = K() Io() exp[ Do3 () + Dray () + Daer (sec(za)) ]


Aerosol particlesMoleculeOzone

Signal received by the Brewer

Brewer’s sensitivity to Io()


ln[ S() ]-Do3- Dray= ln[ K() Io () ]- () * sec(za) +

Y = A * X + B

Langley plot method


Y axis X axisSlope Intercept


Langley plot method 19/06/05 for 320 nm

Y = ln[S()] - Do3 - Dray

A = -() *X = sec(za)+B = ln[K()Io ()]


Selection of clear days for the Langley Plot Method

1. Ozone stdev for individual DS measurements < 2.5 DU

2. za per day 20°

3. Number of good data per day 50

4. Distance between each point and the regression line < 4 (Y unit)

5. Daily mean absolute deviation from the regression line < 0.055 (Y units)





Calibration factor

Average of these 65 calibration factors with error of about 0.2%

65 Calibration factors at Uccle



A O D = ave rag e o f th e 5 ind iv id u a l A O D

A O D = -((Y -B )/X ) fo r ea ch D S m e a sure m e nt

5 m ea n ca lib ra tio n fa cto rs = 5 B

L in e ar re g re ss ion

B e e r law

Summary of the method






4. Results






Where?



If solar intensity too high

Brewer instrument

FilterI1

I2

If not Brewer instrument

I1

I2< I1

What is a Brewer’s filter?



320 nm36

8 nm

sunphotometerTime difference max = 3 min



Filters impact on AOD

c = 0.87

b = 0.80 ± 0.011

a = -0.08 ± 0.004

c = 0.98

b= 0.85 ± 0.004

a= 0.02 ± 0.0014

N = 1718

Standard filters

N = 1934

Real filters

Errors



Where?



Arosa



320 nm36

8 nm

Hourly mean AOD compared for 2002

Brewer spectrophotometer

Sunphotometer



Comparison Arosa/Davos

c = 0.62

b = 0.56 ± 0.04

a = 0.02 ± 0.0006

N = 335




2. The Brewer instrument


Physical equation

Langley plot method

4. Results


Comparisons between different Brewer at the same place




Where?



Uccle 2002-2005

N = 5781

c = 0.98

b= 1.02 ± 0.003

a= 0.06 ± 0.001



Arosa 2004

N = 2771

c = 0.94

b= 0.98 ± 0.006

a= 0.03 ± 0.002



Summary of the comparisons

Brewer 016 040 072

178 0.98

1.02 0.06

156 0.94

0.98 0.03

0.98

0.98 -0.04

072 0.99

0.98 -0.02






Physical equation

Langley plot method

4. Results






Conclusions1. Important role of the filter values of the Brewer

spectrophotometer on the accuracy of AOD

2. High level of confidence of the method used to retrieve the AOD:

correlation coefficient > 0.94

slope ~ 1

Intercept is negligible

3. Validation of the Langley plot method with a comparison between Brewer spectrophotometer and a sunphotometer



Perspectives

1. Application of the method at different Brewer stations

2. Determination of relation between different aerosol parameters: AOD, ssa, type, size and air mass origin


Aerosol Measurements Campaign at Uccle. RMI December 6th 2006.

First preliminary results of the aerosol measurements

campaign at Uccle

RMI team: Anne Cheymol , Alexander Mangold, Hugo De

Backer, Andy Delcloo, René Lemoine and Roeland Van MalderenGhent university team:

Pr. Willy Maenhaut, Wan Wang, Nico Raes, Xuguang Chi and Jan Cafmeyer

Thanks to the weather forecasters of RMI



Overview

1. Objectives of the campaign

2. The instruments and the first preliminary results

3. Perspectives



Objectives

• Aerosol campaign from January 4th to 30th November 2006 at Uccle

• Determination of the relations between AOD, size and type of aerosol particles and air mass origin

Observations in parallel from Brewer spectrophotometer (AOD) and the other aerosol instruments (sampling and monitoring)



Sampling

by Delcloo and Mangold

PM10

Mineral Aerosol

Organic Aerosol

PM2.5

Mineral Aerosol

Organic Aerosol



Sampling

Filter




Inlet

PM10

PM2.5



Ratio PM2.5/PM10



Coarse particle PM10-PM2.5

NO313%

Unexpl.12%

OC*1.416%

Crustal33%

EC1.6%

NH42.0%

Sea Salt17%

Sulphate5%

Elements0.5%

Fine particles PM2.5

OC*1.428%

NH417%

Crustal3.2%

Sea Salt3.0%

Sulphate18%

Elements0.5%

Unexpl.1%

NO326%

EC4%

20% anthropogenic source

61% anthropogenic source



TEOMinlet



Mass concentration of PM2.5

01/02

Mean = 15.4 ug/m3

03/01



1 February 2006

03/0101/02

50 ug/m3



Photo by A. Delcloo and A. Mangold

smoke

28/01 09/11

50 ug/m3

20 ug/m3

20 ug/m3

50 ug/m3



Aethalometer

Mass of Black Carbon



Perspectives 1

1. Determination of the relation between AOD, mass, size and type of the particles and the air mass origin

2. Aerosol studies is foreseen within the Antarctic project with BIRA and Ghent University



Most important perspectives

snoepjes



The END


Antarctic project. RMI December 6th 2006.

The antarctic project


Antarctic project. RMI December 6th 2006.

RMI Ozone/UV/aerosol group

BIRA M. Van Roozendael, M. De Mazière , C. Hermans, D. Gillotay, C. Depiesse, C. Muller,D. Bolsee

Ugent W. Maenhaut and J. Cafmeyer

Members of the project

royal meteorological institute of belgium validation of the method to retrieve the aod and first...

Documents

webseasonal cycle of

different brewer

brewer measurements5

aerosol particlesdirect

aerosol optical depth

aerosol measurements

neutral density filter

mangoldnatural origin