1. Progress on sampling and analysis of carbonaceous aerosols:
The EUSAAR strategy
Jean-Philippe Putaud, Fabrizia CAVALLI, EC-JRC-IES

2. ▪ Positive artifact mitigation ▪ Negative artifact assessment
1 Progress in the validation of the sampling train for particulate carbonaceous matter:
▪ Positive artifact mitigation
▪ Negative artifact assessment
2 Progress in defining a reference method for thermal-optical analysis of OC+ EC:
▪ CEN WG on OC and EC in PM
3 EUSAAR intercomparisons for OC / EC / TC measurements:
▪ Results of the 3rd and 4th intercomparisons
▪ Next intercomparison in 2010
Briefly explain the content of this presentation

3. Positive artifacts 1- POC / EC sampling train validation
▪ Positive OC artifacts contribute 14 – 70 % of particulate OC on
plain QFF (site and season dependent)
▪ Denuder mean performance ranges from 43 to 93% (site and season dependent)
▪ Positive OC artifacts are reduced to 5 – 21 %
The issue of positive artifact has been successfully addressed

4. Negative artifacts: new tests
1- POC / EC sampling train validation
Negative artifacts: new tests
Sampling head
▪ NO news from supplier on special production of suitable sorbents
▪ NO alternative in the very recent literature + blank problems
▪ Tried again quartz fiber filter as back-up filter in two different experiment types
Denuder
Carbon honeycomb monolith
Definition of negative artifact: volatilisation of SVOC from filter-bound aerosol particles.
the assessment of the sampling negative artifact is performed using sorbent substrate back to the front QFF.
C-impregnated glass fiber filters has been usuallproduced by a company disapperaed in the mean time.
The production has therefore stopped and no other suppliers were willing of setting-up special production of such substrates.
Further in the very recent literature no alternative has been proposed and tested and alternative sorbent were chacarteised by strong contaminations and fast aging.
We have decided therefore to test again QFF as sorbents or back up filters in two different exeroments:
Front quartz filter
Back-up filter

5. Two back-up quartz filters
1- POC / EC sampling train validation
Negative artifacts: new tests
Sampling head
24-hr sampling
20 cm/s face velocity
14 < T < 28°C
Denuder
Carbon honeycomb monolith
The first experiment consists of annealing two QFF back to the QFF
Characteristic of the sampling
Front quartz filter
Two back-up quartz filters

6. 1- POC / EC sampling train validation
Negative artifacts: new tests
Describe figure.
Conclusions:
▪ efficiency 80% comparing the amount of OC on the two back-up;
▪ negative artifact = only 3% compared to particulate OC comparing the amount of OC found on the back-up filters with that obtained on the front OC
▪ very limited set of data
Quartz fiber filter as back-up absorbent:
▪ efficiency 80%
▪ negative artifact = only 3% compared to particulate OC
▪ very limited set of data

7. C D A B 1- POC / EC sampling train validation Day i Day i + 1
Negative artifacts: new tests
additionally C D A B
Teflon filters
Sampling head
24-hr sampling
20 cm/s face velocity
Denuder
Alternatively in a more complex a test:
…describe test.
At Day i we performed to parallel aerosol sampling with these identical configuration.
In such configuartion, OC on that filters consists of equations
The filter B sampled at day I is further sampled for 24h the following day with in front a teflon filter to remove particulate OC.
We will have that …equation
We can now compare OC A and C and the difference represents the residual positive artifact and the negative artifact on day i+1
In addiation on day 1+I we determined sampling through the sampling train D the residual positive artifact.
We can now estimate the remianing negative artifact.
Front quartz filter
Day i
Day i + 1

8. 1- POC / EC sampling train validation
Negative artifacts: new tests in Ispra
DAY i A & B OC = OCparticulate i + OCresidual positive art i+ OCnegative art i
DAY i+1 C OC = OCparticulate i + OCresidual positive art. i+ OCnegative art i +
+ OCresidual positive art i+1+ OCnegative art i+1
C-A ΔOC = OCresidual positive art i+1+ OCnegative art i+1
Additionally,
DAY i+1 D OC = OCresidual positive art i+1
This slide was inserted 20 Apr. 2010

9. 1- POC / EC sampling train validation
Negative artifacts: preliminary results
C-A ΔOC = OCresidual positive art i+1+ OCnegative art i+1
D OC = OCresidual positive art i+1
▪ The OCresidual positive art is 0.37  0.17 gC/m3 (0.54  0.21 gC/cm2) in winter and 0.57  0.22 gC/m3 (0.77  0.32 gC/cm2) in summer.
Range confirmed in 2010 tests, 0.42  0.22 gC/cm2.
The negative artifact would represent up to 20% of the OCparticulate
Conclusion

10. 2- Towards a reference method for OC / EC thermal–optical analysis
The EUSAAR_2 protocol
Fraction_Carrier gas
Temp C
Time s
OC1_He
200
120
OC2_He
300
150
OC3_He
450
180
OC4_He
650
EC1_He/O2
500
EC2_He/O2
550
EC3_He/O2
700 70
EC4_He/O2
850 80
Analysis: Thermal optical method developed within the EUSSAR community in which major biases affecting the existing protocol NIOSH and IMPROVE has been mitigated.
F. Cavalli, M. Viana, K. E. Yttri, J. Genberg, and J.-P. Putaud (2010). Toward a standardised thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR protocol.
Atmos. Meas. Tech., 3, 79–89.

11. 2- Towards a reference method for OC / EC thermal–optical analysis
CEN working group on OC /EC
36 resolutions so far
Resolution 3
• Analysis:
EC and OC data should allow/support mass closure of PM along with other PM constituent determined e. g. within the AQD framework. Therefore a mass based technique should be used.
• Links to other standards and network protocols
The European Standard should not be developed in isolation from relevant work in other communities especially EMEP, EUSAAR and the US/Canada.
Resolution 4
WG 35 agrees that the candidate standard method will be based on the analysis of samples collected on filters using the thermal method with optical correction for charring.
The protocol together other is under the evalution of the the CEN working group on OC EC to eentually recieive the status of european standard methods.
The activity of this working group started one year ago and up to now 36 resolution has been taken.

12. CEN working group on OC /EC
2- Towards a reference method for OC / EC thermal–optical analysis
CEN working group on OC /EC
Resolution 5
WG 35 agrees that a literature review and data analysis needs to be undertaken including:
• OC and EC levels in blank filters,
• Artifacts (i.e. filter types),
• Round robin tests,
• Role of carbonates.
These results will feed into an uncertainty assessment.
Resolution 6
WG 35 agrees that a field study is needed to set up a well validated standard.
The field study shall allow the evaluation of different protocols of the thermal method with optical correction for charring. Both optical parameters transmission and reflectance shall be recorded to allow an evaluation of charring correction.
This will include both off-line and on-line analysis.
Remind how these figures are obtained

13. CEN working group on OC /EC
2- Towards a reference method for OC / EC thermal–optical analysis
CEN working group on OC /EC
Resolution 21
To extend and clarify Resolution 7, WG 35 agrees that the choice of analytical protocol for EC and OC (and possibly TC and IC) in the standard shall be based on:
- comparability with one of the three widely-used existing protocols EMEP (EUSAAR2), NIOSH, and IMPROVE, and reproducibility (ie relative insensitivity to small variations in the actual method used)
- lack of systematic bias or interference (eg consideration of the effect of IC, results of analysis of “pure” OC or EC)
practicality (ie time and cost implications).
Remind how these figures are obtained

14. CEN working group on OC /EC
2- Towards a reference method for OC / EC thermal–optical analysis
CEN working group on OC /EC
Resolution 35
Given
-the urgent need for Member States to have a standardised method for EC/OC,
in the absence of a mandate from the Commission (DG ENV),
the WG agrees that they will work on a CEN Technical Report for EC/OC as a priority. This TR will describe several methods (e.g. thermal protocols) that will give different results for EC and OC, because validation data is needed both to specify one standard method and to properly characterise that method.
The standard method will be proposed within 3 years from the mandate from the DG ENV.
Remind how these figures are obtained

15. 3- OC / EC / TC intercalibration - 2008
▪ Ambient aerosol samples collected by 4 partners at their sites (BIR, MSY, KPO, ISP)
▪ Samples distributed to 12 EUSAAR-NA2 partners + 12 associates
▪ Use of the EUSAAR_2 thermal-optical protocol was advised
Remind how these figures are obtained

16. TC relative to avrage TC from EUSAAR partners
3- OC / EC / TC intercalibration
TC relative to avrage TC from EUSAAR partners
On average,
On average, TC carbon can be determined within ±30% error wrt average by
- 10 among 10 EUSAAR partners
- 7 among 9 EUSAAR associates

17. EC / TC relative to EUSAAR _2
3- OC / EC / TC intercalibration
EC / TC relative to EUSAAR _2
To quantify the differences between methods and among laboratories, EC/TC ratios (Fig. 3) are considered. Such ratios are independent of the possible spatial heterogeneities in filter loadings. These data confirm that EC values obtained with NIOSH-like methods are on average 30% lower than the values obtained with the EUSAAR-2 protocol.
On average, EC / TC ratio can be determined within ±30% error wrt average by
▪ 7 among 8 EUSAAR partners
▪ 4 among 9 EUSAAR associates

18. 3- OC / EC / TC intercalibration - 2009
▪ NIST reference material 8785 (urban dust on quartz fibre filter)
▪ Samples distributed to 12 EUSAAR NA2 partners
The last intercomparison (2008) showed that the standard deviation among EUSAAR partners (average 17%) could reach 24% for a single sample collected in Norway (NOR-1). It was first suspected that a fraction of the standard deviation was due to filter loading heterogeneities, but further tests performed later at JRC demonstrated it was not the case. The marginally acceptable standard deviation in TC determination should therefore come from inaccurate measurements by some of the participants. As the true value for ambient samples is unknown, it was impossible to determine which participant was delivering inaccurate values.
That is why it was decided to have an additional intercomparison exercise for carbonaceous species determination with respect to the workplan. This intercomparison (2009) was based on NIST (USA – National Institute of Standards and Technology) reference materials 8785, for which reference values for TC amounts are available. For cost reasons, the intercomparison ws limited to EUSAAR partners.

19. 3- OC / EC / TC intercalibration – NIST reference material
TC amounts (µg / cm²)

20. TC relative to NIST reference values
3- OC / EC / TC intercalibration
TC relative to NIST reference values
Figure 2 shows that the ratio between the TC amount determined by each participant and the reference value ranges 0.87 – 1.55.
It should be noted that the discrepancies observed in 2009 with respect to reference values were not observed in 2008 when comparing the result of each partner to the average values.
To explain these inconsistencies, we first tried to check the calibration of the instrument at the time the reference filters were analyzed. Data were provided by 5 partners only. No obvious problem was detected. To further check the external standard used to calibrate the instrument, it was advised to double check the calibration by injecting known volumes of pure C-containing gases. Results of this test were reported by 2 partners only so far.
It is top important to pursue this investigation to determine whether it is possible that the NIST reference material are getting contaminated while aging, e.g. by trapping volatile OC during storage and transport.

21. EC/TC relative to NIST reference values
3- OC / EC / TC intercalibration
EC/TC relative to NIST reference values
2008
This intercomparison suggests that EUSAAR partners using the EUSAAR_2 protocol obtain EC/TC ratios for the same reference material differing by a factor 1.7. This is not acceptable. The errors in EC/TC seem to be quite systematic: some partners generally report higher values than others.

22. 3- OC / EC / TC intercalibration- NIST reference material
TC : conclusions
▪ most partners report TC values that clearly larger than the ref. value
▪ 2009’ biases cannot explain the ±30% deviation observed in 2008
▪ the overall uncertainties are large => this intercomp. is not stringent
EC /TC : conclusions
▪ EC / TC ratios range from 0.26 to 0.55
▪ differences in line with previous intercomparison
Remind how these figures are obtained

23. fabrizia.cavalli@jrc.ec.europa.eu 3- OC / EC / TC intercalibration
Next intercomparison in 2010
▪ Ambient aerosol samples
▪ Soot loaded filters
In June 2010 punches will be distributed among partners.
EMEP stations reporting OC/EC data are invited to participate
please send an to:
Remind how these figures are obtained

24. Positive artifacts 1- POC / EC sampling train validation
Definition of positive artifact
Characterise and mitigate positive artifact

25. Positive artifact mitigation
1- POC / EC sampling train validation
Positive artifact mitigation
Tests to assess the contribution of positive artifact to the particulate organic carbon has been performed at nine Eusaar stations during different seasons
Assessment of the positive artifact contribution of OC particulate collected on plain QFF filters i.e. without the use of any denuder.
Range % depending on site and season with generally lower contribution in winter.
To mitigate this bias we recommended the use of a honeycomb denuder in front of the QFF.
The efficiency of the denuder has been determined at each background site
Range and lower efficiency in summer.
Positive artifact without denuder: teflon-QFF versus palin QFF
Denuder efficiency: Teflon-QFF versus Teflon-denuder-QFF

26. Positive artifact determination
1- POC / EC sampling train validation
Positive artifact determination
If denuder with such efficiencies are employed the positive artifact is considerably mitigated contributing 5 to 20% of the OC particulate.
If we compare the extent of the positive artifact to the TC aerosol content, we can notice, thathigher contribution of positive artifacts occur when the TC are lower rendering more problematic this bias.

27. 3- OC / EC / TC intercalibration- 2008
EC / TC ratio