A very-non-formal presentationpeople.seas.harvard.edu/~swofsy/BARCA/kenia-draft.pdf · A very-non-formal presentation Kenia T. Wiedemann Nephelometer (3 wavelength) Light scattering

A very-non-formal presentation

Kenia T. Wiedemann

Nephelometer (3 wavelength) Light scattering (450, 525, 636nm)

MAAP (MultiAngle Absorption Photometer) Light absorption (670nm)

CPC (Condensed Particle Counter) Total particles (> 10 nm)

OPC (Optical Particle Counter)+SMPS(Scanning Mobility Particle Sizer) Size distribution

Picarro CO2, CH4,H2O

O3 Analyzer Ozone (of course… ⌐⌐)

Trace gases “The Bottles”

Glossary survey:

Extinction coefficient: it is a measure of attenuation of the light passing through the atmosphere due to the scattering and absorption by aerosol particles.

The variation of the extinction coefficient with wavelength can be presented as a power law function with a constant (related to the power factor) known as the Ångström coefficient.

The Ångström coefficient is inversely related to the average size of the particles in the aerosol: the smaller the particles, the larger the exponent.

Aerosol Optical Thickness is the degree to which aerosols prevent the transmission of light.The aerosol optical thickness (τ) is defined as the integrated extinction coefficient over a vertical column of unit cross section.

Single scattering albedo is the ratio of scattering efficiency to total light extinction.

All these quantities are correlated among them:Scattering Coefficient

Absorption CoefficientAngström coefficient

Single Scattering AlbedoRadiative Forcing

Flights map (BARCA B)

Flight #01 11:33 – 14:06

12:00

12:30

13:00

13:30

•We have flight trajectories plotted in the

region maps, vertical profiles, Angstrom

coefficients, Aerosol Optical Thickness (AOT)

and Single Scattering Albedo calculated for

each flight. We obtained spectral

dependences for the optical properties, and

we intend to obtain the spatial 3D map of the

aerosol optical properties. Some time-

references were signed in the maps to allow

an easy “point-seek”. The timestamps are

UTC time, NOT local time (UTC-4).Alta Floresta

Manaus

Example for a

forest flight(May 17)

Manaus Manaus

2

3

4

5

6

1

1 2 3 4 5 6

% negative/zero scatt coeff values

Flight # Date Period Red Green Blue1 13/05/2009 AM 25 13 2

2 15/05/2009 PM 9 10 9

3 17/05/2009 AM 2 0.4 2

4 17/05/2009 PM 3 5 4

5 19/05/2009 AM 13 16 13

6 19/05/2009 PM 10 15 12

7 21/05/2009 AM 17 15 12

8 21/05/2009 PM 0 0 0

9 22/05/2009 AM 1 2 2

10 23/05/2009 AM 0 0 0

11 23/05/2009 PM 48 5 4

12 26/05/2009 AM 30 12 18

13 26/05/2009 PM 28 6 11

These are the neglected nephelometer data (%). We can see that

from flight#11 we have much more negative/zero values for the red

wavelength. It may be a signature of the presence of high humidity

in the samples*.

During these days the

nephelometer data

nearly didn’t present

negative/zero values.

* 516 nm – 666 nm gaseous absorption bands of H2O and O2.

A lot of negative

values for scattering

coefficient on 636 nm

(red).

Nephelometer : This guy allows us to obtain the scattering coefficient, the Angstrom coefficient, the single scattering albedo (+ MAAP), the aerosol optical thickness (+ MAAP)... (and yes, I love my nephelometer)

How do we obtain the Angström coefficient?

Ecotech Nephelometer: scattering coefficient (SC) for 3 wavelengths: 450nm (blue), 525nm (green) and 636nm (red)

2)(lnlnln cbaSC

AOT = scattering coeff. (SC)+ absorption coeff. (AC). For our

conditions we assumed SC >> AC.

Positive Angström coefficient

Negative Angström coefficient

Usual linear regression (red) against polynomial regression

(black). For the range of the wavelengths we used, the

results may be significantly different.

Example

14:00

14:30 14:40 – 15:00

15:3015:40 – 16:00

Flight #03: 13:43 – 16:12

-61.0 -60.8 -60.6 -60.4

-3.0

-2.8

-2.6

-2.4

-2.2

Latitu

de (

degre

es)

Longitude (degrees)

3.6E-34.7E-35.9E-37.0E-38.2E-39.3E-31.0E-21.2E-21.3E-2

Aerosol Optical Thickness

-61.5 -61.0 -60.5 -60.0

-3.0

-2.5

14:00

14:30 14:40 – 15:00

15:3015:40 – 16:00

Flight #03: 13:43 – 16:12

-61.0 -60.8 -60.6 -60.4

-3.0

-2.8

-2.6

-2.4

-2.2

Latitu

de (

degre

es)

Longitude (degrees)

3.6E-34.7E-35.9E-37.0E-38.2E-39.3E-31.0E-21.2E-21.3E-2

Aerosol Optical Thickness

-61.5 -61.0 -60.5 -60.0

-3.0

-2.5

14:00

14:30 14:40 – 15:00

15:3015:40 – 16:00

Flight #03: 13:43 – 16:12

-61.0 -60.8 -60.6 -60.4

-3.0

-2.8

-2.6

-2.4

-2.2

Latitu

de (

degre

es)

Longitude (degrees)

3.6E-34.7E-35.9E-37.0E-38.2E-39.3E-31.0E-21.2E-21.3E-2

Aerosol Optical Thickness

-61.5 -61.0 -60.5 -60.0

-3.0

-2.5

-61.0 -60.8 -60.6 -60.4

-3.0

-2.8

-2.6

-2.4

-2.2

La

titu

de

(d

egre

es)

Longitude (degrees)

3.6E-34.7E-35.9E-37.0E-38.2E-39.3E-31.0E-21.2E-21.3E-2

Aerosol Optical Thickness

14:00

14:30 14:40 – 15:00

15:3015:40 – 16:00

Flight #03: 13:43 – 16:12

-61.5 -61.0 -60.5 -60.0

-3.0

-2.5

Negative Angström Coefficients

Aerosol scattering that increases with increasing

wavelength = anomalous scattering.

Predominates in remote ocean locations and in remote

continental locations at night.

The predominance of small particles prevents

anomalous aerosol scattering.

What „they‟ say about anomalous scattering:

•Remote ocean locations

•Remote continental locations at night (a much

rarer phenomenon during the day)

•Lack of photochemical aerosol production

•Humidity hysteresis (why does it happen?) also

helps to stablish anomalous scattering

Sun photometer measurements do ocasionally show

anomalous aerosol extinction even in relatively dry

continental locations; nearly associated with lower

turbidity values, indicating aged aerosol not dominated

by local sources (except possibly windblow dust).

(I am investigating that)

The relationship between the Angström coefficient (AC) and the AOT shows that there is a tendency of AC to increase as the AOT(670nm) decreases from 10-4 to 10-6 with aparently three populations in this range.

The AOT plotted here are actually “d(AOT)”. The column integrated shows AOT values about 10-3-10-2 for the vertical profiles, as we could see two slides ago...

-61.0 -60.8 -60.6 -60.4

-3.0

-2.8

-2.6

-2.4

-2.2

La

titu

de

(d

egre

es)

Longitude (degrees)

3.6E-34.7E-35.9E-37.0E-38.2E-39.3E-31.0E-21.2E-21.3E-2

AOT

W.M. Porch [Applied Optics, v. 28, 1178 (1989)]: “The reason this type of aerosol scattering behavior is confined to remote locations,

far from aerosol sources, is that (...) the aerosols have time to coagulate to larger sizes after travel to remote areas. The aerosols

will eventually grow through wet and dry Brownian coagulation processes to particle radii that produce anomalous scattering. (...)

However, new aerosol sources from either direct combustion or gas-to-particle conversion continue to produce particles smaller than

0.5mm.”

Z.D. Adeyewa and E.E. Balogum [Theor. Appl. Climatol. 74, 105 (2003)]: Spectral range 350 – 1038 nm.

They observed anomalous extinction in an Artic air mass between 450 and 600 nm.

13:40

14:00

14:12-14:32

15:02

15:28

13:00

16:00

Flight #09 12:25 – 16:19

13:40

14:00

14:12-14:32

15:02

15:28

13:00

16:00

Flight #09 12:25 – 16:19

13:40

14:00

14:12-14:32

15:02

15:28

13:00

16:00

Flight #09 12:25 – 16:19

13:40

14:00

14:12-14:32

15:02

15:28

13:00

16:00

Flight #09 12:25 – 16:19

13:40

14:00

14:12-14:32

15:02

15:28

13:00

16:00

Flight #09 12:25 – 16:19

African biomass smoke

and/or

Sahara dust?

13:40

14:00

14:12-14:32

15:02

15:28

13:00

16:00

Flight #09 12:25 – 16:19

In hands:-Aerosol optical properties:

-Angstrom coefficient-Single scattering albedo-Aerosol optical thickness

Almost in hands:

•SMPS corrections (temperature/pressure)•3D map of the aerosol optical

properties = Phase A + Phase B

And...

-How (in)homogeneous is the AmazonBasin?-The relationship with the trace gases properties/distribution/concentrations

O3, CO, CO2 (merge data)-Anomalous scattering/extinction? Background condition?-Aerosol transportation (air masses) modelling (inversion model?)