1. Indication of aerosol aging by Aethalometer optical absorption measurements
Luka Drinovec1, Griša Močnik1, Irena Ježek1, Jean-Eudes Petit2,3, Jean Sciare2, Olivier Favez3, Peter Zotter4, Robert Wolf4, André S.H. Prévôt4, and Anthony D.A. Hansen1,5
1. Aerosol d.o.o., Kamniška 41, SI-1000 Ljubljana, Slovenia
2. LSCE (CEA-CNRS-UVSQ), Orme des Merisiers, Gif-sur-Yvette, France;
3. INERIS, Verneuil-en-Halatte, France
4. Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
5. Magee Scientific, 1916A M.L. King Jr. Way, Berkeley, CA 94704, USA
Keywords: Aethalometer, source apportionment, ACSM, AMS, PSCF
Contact author
Presenting author
ACCENT Symposium 2013, Urbino (Italy)

2. 1. Introduction to BC measurements
dpp=20 nm
Note change in scale
dm=472 nm
Sources
- Combustion
Effects of black carbon (BC):
Public health effects
Climate change
How to reduce harmfull effects:
Indentify sources: traffic vs household heating
Indentify sources: local vs. regional

3. Analytical Instrument : Aethalometer™
ATN = ln (I0 / I)
Reference I0
Sensing I BC
Light Source
Filter with Sample
Light Detectors 
babs ~  ATN
Collect sample continuously.
Optical absorption ~ change in ATN.
Measure optical absorption continuously : λ = 370 to 950 nm.
Convert optical absorption to concentration of BC:
BC (t) = babs(t) / 
 - mass absorption crossection
Real-time data: 1 s/1 minute

4. Filter loading effect

5. BC vs ATN analysis – ambient data
k=0.005
k=0.001
Large loading effect
Small loading effect
BC (reported) = BC (zero loading) · { k · ATN }
Linear reduction of the instrumental response due to loading of the filter fiber. Jump at the tape advance (similar to Virkkula (2007) model).
ambient data – no dependence of BC on ATN
slope k variable: site, source, aerosol age, composition
need to determine it dynamically – do not assume, rather measure

6. Dual spot Aethalometer – AE33
ATN1 = ln (I0 / I1)
Reference I0
Sensing I1
BC1
Light Source
Filter with Sample
Light Detectors 
Sensing I2
ATN2 = ln (I0 / I2)
BC2
Two parallel spots with different flow, therefore ->
From different loading and attenuation loading compensation parameter k(λ) is calculated.
Absorption data is compensated:
babs=babs1/(1-k*ATN1)
Payerne Winter 2013

7. BC source apportionment
measure attenuation with the Aethalometer
absorption coefficient - babs
for pure black carbon: babs ~1/λ
generalize Angstrom exponent: babs ~1/λα
diesel: α ≈ 1
wood-smoke: α ≈ 2 and higher
J. Sandradewi et al., A study of wood burning and traffic aerosols in an Alpine valley using a multi-wavelength Aethalometer, Atmospheric Environment (2008) 101–112

8. BC source apportionment
b(λ) = bwb (λ,wood) + bff (λ,fossil) λ = 470 nm, 950 nm
bi(470 nm) / bi (950 nm) = (470 nm / 950 nm) -
α = 1,0 ± 0,1 (fossil) Bond & Bergstrom 2004
α = 2,0 -0,5/+1,0 (wood) Kirchstetter 2004,
Day 2006,
Lewis 2008
BCwb
BCff
Sandradewi 2008

9. Measurement campaign EMEP: summer 2012 & winter 2013 Paris site
- SIRTA Atmospheric Research Observatory
- located in a semi-urban environment
- 25 km south of the Paris city center
Payerne site
- Payerne aerological station
- Rural background site
- NW Swiss
Site
Campaign
BC (ng/m3)
Biomass burning (%)
Payerne
Winter 2013
789 29
Summer 2012
593 10
Paris
968 25
671 4

10. Back trajectory analysis
Back trajectory analysis using Potential Source Contribution Function (PSCF)
Represents the probability that an air parcel may be responsible for high concentrations observed at the receptor site
72h back trajectories calculated with Hysplit v4.9
starting at 500m AGL
An example:
- PSCF analysis of BC
- Paris winter 2013

11. Indentification of source locations
- Angstrom exponent α obtained from AE33 spectral data
- PSCF (Back trajectory analysis using Potential Source Contribution Function)
α < 1.3 (traffic emissions)
α > 1.3 (biomass burning)
Paris – EMEP winter campaign 2013

12. Differentiation of fresh and aged aerosols
Payerne summer
Payerne winter
Spectral fingerprint
Summer and winter aerosols have different optical properties - k(λ)
For background locations with aged aerosol loading effect at 880 nm (where BC is measured) is small!

13. Differentiation of fresh and aged aerosols
- Compensation parameter k880nm obtained from AE33
- PSCF (Back trajectory analysis using Potential Source Contribution Function)
k880nm>0.002 (fresh aerosols)
k880nm<0.002 (aged aerosols)
Paris – EMEP summer campaign 2012

14. Particle coating hypotesis
Changes in k(λ) are caused by transparent coating
SMPS:
Fresh soot particle size = nm
Aged particle size > 100 nm
Particle diameter [nm]

15. Particle coating hypotesis
Coating factor (CF) – ratio between the sum of nonrefractory aerosol mass to BC:
CF = (Org + NH4 + SO4 +NO3)/BC
Aerosol mass spectrometers:
ACSM & AMS (Aerodyne)
-> Aerosol chemical composition is obtained

16. Particle coating hypotesis – summer data
AE33 compensation parameter
Paris Summer2012 campaign
ACSM
Compensation parameter k880nm and coating factor correlate well.

17. Summary
Spectral absorption data from Aethalometer AE33 was used for BC source apportionment during EMEP campaigns in Paris (France) and Payerne (Switzerland).
Back trajectory analysis using Potential Source Contribution Function (PSCF) was used to determine fossil fuel and biomass burning locations.
PSCF: Aged aerosols have small k880nm
Aethalometer and ACSM/AMS measurements were used for calculation of the coating factor (CF): Big CF = Small k880nm

18. Thank you for your attention!
Acknowledgements
The work described herein was co-financed by the EUROSTARS grant E!4825 and JR-KROP grant Measurements performed at SIRTA (LSCE) were funded by CNRS, CEA, the EU-FP7( ) 'ATRIS' project under grant agreement n°262254, the Primequal Predit 'PREQUALIF' project (ADEME contract n°1132C0020), and the DIM R2DS (AAP 2010) 'PARTICUL'AIR' project. Measurements in Payerne were conducted by the Swiss Federal Office for the Environment (FOEN).
Thank you for your attention!