Particles size and composition in Mediterranean countries:
MED-PARTICLES Project 2011-2013
geographical variability and short-term health effects
Under the Grant Agreement EU LIFE+ ENV/IT/327
Particles size and composition in Mediterranean countries:
geographical variability and short-term health effects
MED-PARTICLES
ACTION 4.
Inter-comparison campaigns
Summary: In Action 4 of the MED-PARTICLES project it was stated to carry out intercomparisons aimed to harmonize the analytical procedure of the participating groups, to
highlight possible bias in the methods and to be of help in the interpretation of the differences
between the results.
In order to take into account the seasonal differences in PM composition, two intercomparison were scheduled, the first one during the summer 2012 and the second one during
the winter 2012-2013. The results are discussed in this report.
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MED-PARTICLES INTER-COMPARISON
SUMMER AND WINTER STUDIES
C. Perrino (CNR-IIA)
M. Catrambone, A. Pietrodangelo, S. Dalla Torre, E. Rantica, T. Sargolini (CNR-IIA)
T. Maggos (NCSR DEMOKRITOS, Athens-GR);
N.Perez, J. Pey (IDÆA-CSIC, Barcelona-ES);
I. Ricciardelli (ARPAER, Bologna-I),
A. Sánchez de la Campa Verdona,(University of Huelva, Huelva-ES)
C.N.R. Institute of Atmospheric Pollution Research
SAMPLING
Samplings were carried at the measurement station “Arnaldo Liberti” sited inside the
C.N.R. Research Area RM1 of Montelibretti, Rome (Google Earth co-ordinates: 42° 06’ 20,81”N
12° 38’ 23,92” E). The sampling periods were between July 23rd and August 4th and between
December 8th and 20th, 2012.
Eight identical sampling lines were displayed, side-by-side, to collect PM10 on Teflon or
quartz membrane filters. Three HYDRA Dual Sampler (Figure 1) and one SWAM5a Dual
Channel Monitor (FAI Instruments, Fontenuova, Rm) were used. Each instruments operated
at the flow rate of 2.3 m3/h on two identical channels, each one equipped with its own PM 10
sampling head, compliant with EN 12341. In addition
to the sampling step, SWAM5a Dual Channel Monitor
also determined PM mass concentration by the beta
attenuation method. As samplers, both SWAM 5a DC
Monitor and HYDRA are certified by TUV as reference
samplers. Sampling duration was 24 hours, from
midnight to midnight.
Five analytical laboratories taking care of the
chemical analysis of PM in the MED-PARTICLES
framework participated to the inter-comparison: two
from Spain (one taking care of the analyses from
Huelva, code SP1, the other one of the analyses from
Barcelona and Madrid, code SP2), one from Greece
(taking care of the analyses from Penteli, Athens and
Aegina, code GR), two from Italy (one taking care of
the analyses from Emilia Romagna, code ER, the other
one of the analyses from Rome-Montelibretti, code
ML). According to the sampling procedure used at the
different MED-PARTICLES sites, six sampling lines
were then equipped with quartz fiber filters (2 for
Spain, 1 for Greece, 2 for Italy, 1 spare one), while two
sampling lines were equipped with Teflon filters (1
for Italy, 1 spare one).
Figure 1: HYDRA Dual Sampler.
PM mass collected on the sampled filters was
determined by gravimetry, using an analytical balance and robot (Sartorius) with sensitivity
10-6 g (Figure 2). Conditioning of the filters was carried out according to the procedure
detailed in EN12341. Five groups of five replicates were carried out for weighting each filter,
both before and after sampling. Additionally, on the two Teflon filters the collected mass was
also determined by the beta attenuation method.
Additional check of the quality of the replicate samplings was carried out by performing
ED-XRF analysis of the collected mass.
Figure 2: Analytical balance and robot
After evaluating the results of the element and mass determinations, the filters collected
during 10 out of the 13 sampling days of each period passed the quality analysis and were
chosen for the inter-comparison. Selected periods were July 24 - 30 and August 1-3 for the
summer inter-comparison, December 11th – 20th for the winter inter-comparison. In addition
to the good reproducibility of the mass and of the elemental concentration, the sampling
periods were chosen also with the aim to obtain the widest concentration range.
For both periods, six out of eight of the collected replicate series of samples, the most
performing ones, were chosen to be distributed among the participating laboratories, which
had to carry out the analyses and send the results back within two months. The two spare
series were taken at CNR-IIA.
PM10 mass concentration and standard deviation between the two replicates during the
selected days of the two periods, as determined by the SWAM 5a Dual Channel Monitor, are
reported in Table I . Concentration data are also shown in Figure 3.
Table I: PM10 concentration during the selected days in the summer and the winter period.
July 24
July 25
July 26
July 27
July 28
July 29
July 30
August 1
August 2
August 3
Conc.
g/m3
15.0
17.9
29.8
32.1
31.1
40.2
35.5
39.1
32.6
31.8
St. dev.
g/m3
0.14
0.21
0.21
0.02
0.64
0.71
1.71
0.21
0.07
0.10
December 11
December 12
December 13
December 14
December 15
December 16
December 17
December 18
December 19
December 20
Conc.
g/m3
22.8
38.2
62.2
39.3
26.9
31.8
15.7
17.7
12.7
31.4
St. dev.
g/m3
0.28
1.04
0.57
1.10
0.36
0.33
0.69
0.89
1.12
0.86
PM10
70
concentration (g/m 3 )
60
50
40
30
20
10
0
jul 24 jul 25 jul 26 jul 27 jul 28 jul 29 jul 30 aug 1 aug 2 aug 3
PM10
70
concentration (g/m 3 )
60
50
40
30
20
10
0
11-dic 12-dic 13-dic 14-dic 15-dic 16-dic 17-dic 18-dic 19-dic 20-dic
Figure 3: PM10 concentration during the selected days during the summer and winter periods.
CHOICE OF THE SERIES OF FILTERS
The results of the XRF determinations of selected elements on the sampled filters were
used to evaluate the quality of the sampling phase. XRF determination of these elements, in
fact, proved to be more reliable than the gravimetric determination of the mass. Selected
elements were Ca, Fe, K, Mn and V. The results of the elemental analyses (five elements, three
replicate analyses for each element) were pooled and the per cent difference with respect to
the average value of the eight series of samples was calculated for each day. Figure 4 shows
the results obtained for the best six series of filters during the summer inter-comparison. Per
cent variation for the selected series were generally below 5% and the differences were
randomly distributed around zero. Similar results were obtained during the winter intercomparison.
15
10
5
s. 6
s. 5
%
s. 4
0
s. 3
s. 2
s. 1
-5
-10
-15
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
Figure 4: Per cent variation of the elemental concentration with respect to the average value
among the six series of selected samples (five elements, three replicates for each element).
For both inter-comparisons, the best six series of filters were casually distributed among
the participating groups, as follows.
SUMMER INTER-COMPARISON:
- Series n.1: lab code ER, Italy (I. Ricciardelli, ARPA Emilia Romagna, Bologna);
- Series n.2: lab code SP2, Spain (J. Pey, IDÆA-CSIC, Barcelona);
- Series n.3: lab code GR, Greece (T. Maggos, NCSR DEMOKRITOS, Athens);
- Series n.4: lab code ML - Teflon filters - Italy (M. Catrambone, CNR-IIA, Montelibretti);
- Series n.5: lab code ML, Italy (T. Sargolini, CNR-IIA, Montelibretti);
- Series n.6: lab code SP1, Spain, (A. Sánchez de la Campa Verdona, University of Huelva).
WINTER INTER-COMPARISON:
- Series n.1: lab code GR, Greece (T. Maggos, NCSR DEMOKRITOS, Athens);
- Series n.2: lab code SP2, Spain (N. Perez, IDÆA-CSIC, Barcelona);
- Series n.3: lab code ML - Teflon filters - Italy (M. Catrambone, CNR-IIA, Montelibretti);
- Series n.4: lab code SP1, Spain, (A. Sánchez de la Campa Verdona, University of Huelva);
- Series n.5: lab code ER, Italy (I. Ricciardelli, ARPA Emilia Romagna, Bologna);
- Series n.6: lab code ML, Italy (T. Sargolini, CNR-IIA, Montelibretti).
RESULTS
The participating groups used the inter-comparison filters to carry out the same types of
analyses they carried out on their own filters in the framework of the MED-PARTICLES
project. Ionic content was determined by ion chromatography by groups GR and ML.
Elemental content was determined by ICP-AES and ICP-MS by groups SP1 and SP2 and by EDXRF by group ML. Elemental carbon and organic carbon were determined by all groups (SP1,
SP2, GR, ER, ML) by thermo-optical analysis, using a Sunset analyzer. The thermal protocol
was NIOSH QUARTZ for all groups except ER, where EUSAAR 2 was used. Three blanks filters
were sent to each group and the average blank values were subtracted from the results
yielded by each group.
Determination of ions: summer inter-comparison
The results of the ionic analyses carried out by GR and ML groups are reported in Table
II. Figure 5 show a visual comparison of the data, which are in fairly good agreement only for
sulphate, ammonium, magnesium and calcium (average percent differences of the ten samples
below 10%, maximum percent differences below 30%). The other ions (chloride, nitrate,
sodium, potassium) showed average percent differences from 20% (sodium) to 26%
(chloride; for this ions the calculation was run on 7 samples only because three of them were
below the quantitation limit), with maximum percent difference up to 50%.
More information about the reliability of the two data sets can be obtained by
comparing, for soluble species only, the results obtained by ion chromatography with those
obtained by ICP and by XRF (see below).
Table II: Comparison of the ion concentrations, expressed in g/m3,
determined by groups GR and ML – summer period
jul 24
GR
GR
GR
GR
GR
GR
GR
GR
GR
jul 25
jul 26
jul 27
jul 28
jul 29
Cl0.036
0.024 0.089
NO3- 0.30
0.45
0.81
1.1
1.2
SO4=
2.7
3.1
4.8
4.5
4.8
PO4= b.d.l. 0.047 0.021 0.084 0.10
Na+
0.32
0.11
0.21
0.29
0.28
NH4 0.93
1.1
1.6
1.5
1.6
K+
0.12 0.043 0.072 0.20
0.23
Mg2+ 0.076 0.031 0.043 0.055 0.058
Ca2+ 0.35
0.44
0.99
1.6
1.5
0.13
2.4
6.1
0.13
1.0
1.7
0.57
0.14
1.6
jul 30
aug 1
aug 2
aug 3
0.048 0.058 0.031
2.3
2.4
2.0
3.2
5.3
4.3
0.11
0.14
1.1
0.89
0.60
0.87
1.7
1.2
0.45
0.26
0.12
0.14
0.12 0.091
2.0
2.6
2.2
jul 24
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
Cl0.043 0.032 0.045 0.047 0.043 0.065 0.073 0.067 0.043 0.078
NO3- 0.44
0.53
0.76
0.77
0.57
1.6
1.6
1.7
1.0
0.96
SO4=
2.7
3.3
5.1
4.0
3.6
5.2
3.9
2.9
3.0
3.2
Na+
0.23
0.17
0.27
0.25
0.21
0.68
0.67
0.69
0.38
0.37
NH4+ 0.95
1.3
1.8
1.4
1.2
1.3
0.97
0.70
0.99
1.1
K+
0.13
0.13
0.19
0.24
0.22
0.48
0.22
0.39
0.14
0.19
Mg++ 0.063 0.049 0.065 0.067 0.062 0.15
0.13
0.13 0.093 0.086
Ca++ 0.26
0.31
1.1
2.1
1.8
1.5
2.1
2.6
2.4
2.1
NITRATE
CHLORIDE
3.0
0.2
GR
GR
0.1
ML
ML
2.5
0.1
2.0
g/m3
g/m3
0.1
0.1
1.5
0.1
1.0
0.0
0.5
0.0
0.0
0.0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
jul 24
aug 3
jul 25
jul 26
SULPHATE
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 29
jul 30
aug 1
aug 2
aug 3
jul 29
jul 30
aug 1
aug 2
aug 3
jul 29
jul 30
aug 1
aug 2
aug 3
SODIUM
7.0
1.2
GR
GR
6.0
ML
1.0
ML
5.0
g/m3
g/m3
0.8
4.0
0.6
3.0
0.4
2.0
0.2
1.0
0.0
0.0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
AMMONIUM
jul 28
0.6
GR
GR
1.8
ML
ML
0.5
1.6
1.4
0.4
g/m3
1.2
g/m3
jul 27
POTASSIUM
2.0
1.0
0.3
0.8
0.2
0.6
0.4
0.1
0.2
0.0
0.0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
jul 28
CALCIUM
MAGNESIUM
3.0
0.2
GR
GR
0.1
ML
ML
2.5
0.1
2.0
g/m3
0.1
g/m3
ML
ML
ML
ML
ML
ML
ML
ML
jul 25
0.1
1.5
0.1
1.0
0.0
0.5
0.0
0.0
0.0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
jul 28
Figure 5: Comparison of the results obtained by GR and ML in the IC analysis of ions.
Determination of ions: winter inter-comparison
The results of the ionic analyses carried out by GR and ML groups are reported in Table
III. Figure 6 show a visual comparison of the data.
The results are in perfect agreement for sulphate only (average percent differences of
the ten samples: 3.8%; maximum percent differences: 7.1%). Chloride, nitrate, sodium,
ammonium, potassium and magnesium show a very similar time pattern and good
performance at the regression analysis in terms of Pearson coefficient (between 0.854 of
ammonium, and 0.997 of sodium). However, for these ions the ML values are always higher
than the GR values, with slopes between 1.15 (sodium) and 1.86 (magnesium). For this
reason, the average percent differences of the ten samples vary between 10% (potassium)
and 44% (ammonium). Calcium shows the most disagreeing pattern, but the percent
difference of the ten samples is similar: 24% as average, 39.5 as maximum). The very good
agreement obtained for sulphate and the coherence of the time patterns for all ions indicate
that calibration differences between the two group most probably occurred.
Table III: Comparison of the ion concentrations, expressed in g/m3,
determined by groups GR and ML – winter period
dec 11 dec12 dec 13 dec 14 dec 15 dec 16 dec 17
dec 18
dec 19 dec 20
GR
Cl-
0.070
0.14
0.37
0.26
0.30
1.3
0.51
0.070
0.060
0.15
GR
NO3-
1.8
2.7
5.5
3.3
2.4
3.0
1.6
2.5
1.6
3.1
GR
SO4=
0.83
0.74
1.1
1.2
2.4
2.1
1.0
1.0
0.91
1.0
GR
Na+
0.12
0.10
0.050
0.15
0.50
1.5
0.50
0.06
0.10
0.09
GR
NH4
0.20
0.19
0.49
0.42
0.44
0.12
0.060
0.53
0.26
0.19
GR
K+
0.34
0.61
1.01
0.71
0.27
0.30
0.42
0.34
0.25
0.58
GR
Mg2+ 0.014 0.015 0.015 0.024 0.064
0.16
0.064
0.014
0.014 0.025
GR
Ca2+
ML
Cl-
0.33
0.24
0.50
0.29
0.90
0.52
0.45
0.48
0.34
0.56
0.27
2.0
0.25
0.82
n.d.
0.21
0.28
0.17
0.82
0.21
ML
NO3-
2.5
3.6
6.7
4.3
2.8
3.8
1.9
4.0
2.2
3.1
ML
SO4=
0.93
0.86
1.1
1.3
2.3
2.2
1.1
1.1
0.9
0.9
ML
Na+
0.28
0.24
0.15
0.30
0.71
1.9
0.80
0.16
0.20
0.20
ML
NH4+
0.58
0.54
0.88
0.84
0.89
0.63
0.33
1.1
0.60
0.39
ML
K+
0.44
0.78
1.2
0.88
0.33
0.38
0.50
0.44
0.29
0.67
Mg++ 0.046 0.037 0.031 0.049
1.1
1.3
0.57
Ca++ 0.46
0.14
0.31
0.15
0.034
0.029 0.035
0.15
0.15
0.58
0.0059
0.23
ML
ML
1.2
CHLORIDE
NITRATE
8
2.5
GR
GR
7
ML
ML
2.0
5
1.5
g/m3
g/m3
6
1.0
4
3
2
0.5
1
0.0
0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
SULPHATE
SODIUM
2.5
2.5
GR
GR
ML
ML
2.0
2.0
g/m3
g/m3
1.5
1.5
1.0
1.0
0.5
0.5
0.0
0.0
dec 11
dec 12
dec 13
dec 14
dec 15
dec 16
dec 17
dec 18
dec 19
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 20
AMMONIUM
POTASSIUM
1.4
1.4
GR
GR
ML
1.2
ML
1.0
1.0
0.8
0.8
g/m3
g/m3
1.2
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
MAGNESIUM
CALCIUM
0.35
1.4
GR
GR
0.30
0.20
0.8
g/m3
1.0
g/m3
0.25
0.15
0.6
0.10
0.4
0.05
0.2
0.00
ML
1.2
ML
0.0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
Figure 6: Comparison of the results obtained by GR and ML in the IC analysis of ions.
Determination of elements: summer inter-comparison
The results of the elemental analyses carried out by ICP (SP1 and SP2 groups) and XRF
(ML group) are reported in Table IV. Only elements used for the MED-PARTICLES database
have been considered for the inter-comparison (Mg, Al, Ca, K, Fe, Ti, V, Cr, Mn, Ni, Cu, Zn, As,
Pb). Figures 7 and 8 show a visual comparison of the data.
Table IV: Comparison of the element concentrations determined by groups ML, SP1, SP2.
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
Mg
Al
Ca
K
Fe
Ti
V
Cr
Mn
Ni
Cu
Zn
As
Pb
jul 24
jul 25 jul 26 jul 27 jul 28
jul 29
g/m3 0.072
g/m3 0.14
g/m3 0.67
g/m3 0.22
g/m3 0.12
ng/m3 8.9
ng/m3 1.2
ng/m3 4.6
ng/m3 5.3
ng/m3 0.96
ng/m3 8.5
ng/m3
13
ng/m3 0.91
ng/m3 4.8
0.010 0.051 0.057 0.045
0.21 0.36 0.41 0.44
0.78
1.7
2.4
1.9
0.25 0.36 0.43 0.42
0.21 0.35 0.36 0.43
18
35
36
41
2.4
4.5
4.2
4.4
4.9
7.7
9.1
6.1
7.6
12
13
13
1.6
3.4
2.8
2.3
12
14
14
16
11
17
20
15
1.2
1.6
1.3
1.5
4.6
5.4
7.3
7.7
0.21
0.75
2.2
0.85
0.63
77
8.5
7.0
16
3.0
17
18
1.8
9.0
SP1 Mg g/m3
SP1 Al g/m3
SP1 Ca g/m3
SP1 K g/m3
SP1 Fe g/m3
SP1 Ti ng/m3
SP1 V ng/m3
SP1 Cr ng/m3
SP1 Mn ng/m3
SP1 Ni ng/m3
SP1 Cu ng/m3
SP1 Zn ng/m3
SP1 As ng/m3
SP1 Pb ng/m3
0.19
0.33
0.86
0.59
0.31
jul 30 aug 1 aug 2 aug 3
0.076 0.080 0.049
0.63 0.45 0.43
2.4
3.0
2.7
0.51 0.65 0.36
0.52 0.45 0.49
65
46
45
8.4
5.8
5.9
6.0
8.1
5.5
15
16
14
2.3
2.6
2.9
13
18
19
12
21
14
0.7
1.4
1.2
6.2
7.6
5.6
0.049
0.45
2.4
0.36
0.45
45
7.3
4.8
11
3.2
16
20
0.95
6.7
0.82
13
0.23
0.55
2.3
0.55
0.56
37
1.7
13
0.31
0.79
4.1
0.71
0.79
44
2.4
15
0.28
0.70
2.7
0.68
0.76
48
3.2
18
0.26
0.71
2.0
0.69
0.72
41
2.4
11
0.45
1.0
2.2
1.2
1.0
76
5.8
6.8
0.55
0.96
5.5
0.96
0.95
756
7.4
20
0.40
0.81
4.4
1.1
0.82
244
4.0
16
0.45
1.1
7.8
0.92
1.08
96
3.8
13
0.32
0.85
2.6
0.71
0.82
69
4.6
13
9.0
9.6
33
0.56
4.2
9.1
12
28
0.61
5.7
9.8
15
34
0.88
7.0
8.5
17
37
0.81
9.2
6.4
13
22
0.58
8.0
9.5
21
35
0.74
9.2
14
20
51
1.1
9.8
8.9
21
47
0.99
10
15
19
39
0.78
7.2
13
17
34
0.60
11
SP2 Mg g/m3 0.083
SP2 Al g/m3 0.60
SP2 Ca g/m3 0.44
SP2 K g/m3 0.16
SP2 Fe g/m3 0.19
SP2 Ti ng/m3
14
3
SP2 V ng/m
0.79
SP2 Cr ng/m3 3.8
SP2 Mn ng/m3 6.4
SP2 Ni ng/m3 0.73
SP2 Cu ng/m3 7.4
SP2 Zn ng/m3
23
SP2 As ng/m3 0.51
SP2 Pb ng/m3 4.3
* ICP-AES value
0.084
0.40
0.50
0.17
0.30
20
2.0
3.6
6.5
1.2
10
16
0.59
4.5
0.12
0.57
1.1
0.21
0.47
34
2.9
6.5
11
1.7
11
19
0.78
6.5
0.16
0.75
2.0
0.36
0.61
37*
4.1*
15*
1.1*
13*
26*
9.6*
0.15
0.83
1.3
0.39
0.58
42
3.1
3.0
13
0.79
14
22
0.67
9.0
0.33
1.5
1.4
0.71
0.81
71
6.7
6.6
16
2.8
15
17
0.66
9.5
0.25
1.2
1.5
0.39
0.66
59
6.5
2.4
14
1.6
10
15
0.66
9.1
0.22
0.92
1.8
0.49
0.58
42
3.5
8.5
16
2.7
14
21
0.69
7.8
0.17
0.96
1.7
0.19
0.64
39
4.2
2.9
16
4.3
15
20
0.69
5.9
0.17
1.0
1.5
0.21
0.63
41
5.3
3.0
15
4.7
15
21
0.56
12
Mg
0.6
Al
1.6
SP1
ML
SP2
0.5
SP1
ML
SP2
1.4
1.2
g/m3
g/m3
0.4
0.3
1.0
0.8
0.6
0.2
0.4
0.1
0.2
0.0
0.0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
Ca
9
jul 29
jul 30
aug 1
aug 2
aug 3
jul 29
jul 30
aug 1
aug 2
aug 3
jul 29
jul 30
aug 1
aug 2
aug 3
K
1.4
SP1
ML
SP2
8
jul 28
SP1
ML
SP2
1.2
7
1.0
g/m3
g/m3
6
5
4
0.8
0.6
3
0.4
2
0.2
1
0
0.0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
Fe
1.2
Ti
800
SP1
ML
SP2
1.0
jul 28
SP1
ML
SP2
700
600
ng/m3
g/m3
0.8
0.6
500
400
300
0.4
200
0.2
100
0
0.0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
jul 28
Figure 7: Comparison of the results obtained by SP1, ML and SP1 in the analysis of some elements.
v
9
Cr
25
SP1
ML
SP2
8
SP1
ML
SP2
20
7
ng/m3
ng/m3
6
5
15
4
10
3
2
5
1
0
0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
Mn
18
jul 29
jul 30
aug 1
aug 2
aug 3
jul 29
jul 30
aug 1
aug 2
aug 3
jul 29
jul 30
aug 1
aug 2
aug 3
jul 29
jul 30
aug 1
aug 2
aug 3
Ni
16
SP1
ML
SP2
16
jul 28
SP1
ML
SP2
14
14
12
ng/m3
ng/m3
12
10
10
8
8
6
6
4
4
2
2
0
0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
Cu
25
jul 28
Zn
60
SP1
ML
SP2
SP1
ML
SP2
50
20
ng/m3
ng/m3
40
15
30
10
20
5
10
0
0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
As
2.0
Pb
14
SP1
ML
SP2
1.8
jul 28
SP1
ML
SP2
12
1.6
10
ng/m3
ng/m3
1.4
1.2
1.0
8
6
0.8
0.6
4
0.4
2
0.2
0.0
0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
jul 28
Figure 8: Comparison of the results obtained by SP1, ML and SP1 in the analysis of some elements.
As far as the concentration levels are concerned, the time series of two groups (SP2 and
ML) using different analytical techniques (ICP and XRF, respectively) were in better
agreement than the two time series obtained by the two groups using the same technique
(SP1 and SP2). This is particularly true for Mg, Ca, K, Fe, Ti, Cr, Ni and Zn. Considering the per
cent difference with respect to the average of the three data series on the whole dataset (14
elements, 10 days) we have + 37% for SP1 and -17% for both SP2 and ML. Considering the
average of only SP2 and ML data, the per cent difference was below 2% for Ti and Mn, below
10% for Cu and Pb, below 20% for Ni, Zn, K, Fe, V, Cr and above 20% for Mg, Al, Ca and As.
A more reliable analysis of the differences between the three series of values can be
carried out by performing a linear regression between the three possible pairs of datasets.
The results are reported in Table V. A very good agreement is obtained by all three groups for
the analysis of V and Fe (Pearson’s coefficient in all cases higher than 0.8). When considering
only SP2 and ML, Pearson’s coefficient was better than 0.9 for six elements (V, Fe, Ca, K, Ti, Cu)
and bad results were obtained only for Zn and As. Much worse results are obtained when
comparing SP2 with SP1 and SP1 with ML.
Table V: Pearson’s coefficient (R2) for the pairs of datasets in summer inter-comparison
ELEMENT
SP2 vs. ML
SP2 vs. SP1
SP1 vs. ML
Mg
Al
Ca
K
Fe
Ti
V
Cr
Mn
Ni
Cu
Zn
As
Pb
0.67
0.86
0.92
0.93
0.95
0.99
0.97
0.69
0.83
0.42
0.91
0.11
0.39
0.51
0.65
0.57
0.26
0.61
0.80
0.19
0.92
0.02
0.21
0.71
0.38
0.80
0.85
0.22
0.90
0.07
0.43
0.46
0.14
0.26
0.82
0.08
0.59
0.01
0.01
0.46
Figure 9 reports the comparison of three elements that are not included in the
MEDPARTICLES database but can be of help in evaluating the inter-comparison of ion
chromatography results. Sodium, sulphate and chloride, in fact, are present in atmospheric
PM as soluble species; therefore, comparable results are expected by IC and by elemental
analysis. The results in Figure 9 shows that concentration levels and time pattern of the IC
analysis carried out by ML and the elemental analyses carried out by ML and SP2 are in very
good agreement, suggesting that ML data series for IC analyses are reliable.
Na (by elemental analysis)
Na+ (by Ion Chromatography)
1.2
1.2
SP1
ML
SP2
GR
ML
1.0
1.0
0.8
g/m3
g/m3
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
SULPHATE (by Ion Chromatography
7
GR
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
aug 2
aug 3
aug 2
aug 3
SP1
ML
SP2
6
ML
5
g/m3
5
4
g/m3
jul 27
SULPHATE (by elemental analysis)
7
6
jul 26
4
3
3
2
2
1
1
0
0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
jul 24
aug 3
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
Cl (by elemental analysis)
Cl- (by Ion Chromatography
0.16
0.16
GR
0.14
ML
0.14
ML
0.12
0.10
0.10
g/m3
g/m3
0.12
0.08
0.08
0.06
0.06
0.04
0.04
0.02
0.02
0.00
0.00
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
Figure 9: Comparison of the results obtained for species analyzed by both IC and ICP or XRF.
Determination of elements: winter inter-comparison
The results of the elemental analyses carried out by ICP (SP1 and SP2 groups) and XRF
(ML group) during the winter inter-comparison are reported in Table VI. Only elements used
for the MED-PARTICLES database have been considered (Mg, Al, Ca, K, Fe, Ti, V, Cr, Mn, Ni, Cu,
Zn, As, Pb). Figures 10 and 11 show a visual comparison of the data.
Table VI: Comparison of the element concentrations determined by groups ML, SP1, SP2.
0.053 0.043 0.043 0.13 0.29 0.13 0.031 n.d.
0.11 0.11 0.04 0.09 0.08 0.08 0.065 0.07
0.87 1.46 0.68 0.38 0.40 0.35 0.18 0.36
0.96
1.2
0.83 0.38 0.44 0.59 0.51 0.35
0.18 0.23 0.15 0.037 0.094 0.079 0.047 0.083
8.9
8.7
3.6 3.361 2.0
0.75
n.d.
n.d.
1.2
1.8
2.0
4.9
5.2
2.0
n.d.
n.d.
12
13
9.1
3.8
3.9
4.3
8.5
8.0
9.2
9.0
3.7
2.7
3.4
2.9
3.1
4.4
3.0
7.5
3.8
2.4
2.4
2.4
2.3
1.8
17
17
12
8.7
12
11
11
11
32
45
22
12
14
13
17
13
n.d.
0.99 0.85 0.67
n.d.
n.d.
0.48
n.d.
8.1
13
6.6
7.4
8.6
6.5
6.6
5.2
dec
20
0.052
0.16
1.26
0.72
0.19
14
1.1
13
9.0
2.9
17
22
0.56
6.5
0.073 0.071 0.073 0.12
0.38 0.59 0.61 0.25
1.2
1.1
1.2
0.87
0.82
1.2
1.2
0.42
0.24 0.30 0.31 0.083
17
18
19
n.d.
0.66
1.1
1.1
3.6
7.6
8.3
7.6
0.7
9.9
11
11
n.d.
5.9
7.0
5.3
3.3
11
12
11
2.7
28
42
25
13
0.56 0.63 0.62 0.33
9.9
31
14
29
0.087
0.61
1.0
0.47
0.27
n.d.
0.69
7.4
9.5
3.4
8.7
19
0.32
12
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
ML
Mg
Al
Ca
K
Fe
Ti
V
Cr
Mn
Ni
Cu
Zn
As
Pb
g/m3 0.038
g/m3 0.06
g/m3 0.48
g/m3 0.46
g/m3 0.11
ng/m3 0.57
ng/m3 1.1
ng/m3 6.5
ng/m3 4.8
ng/m3 2.5
ng/m3
11
3
ng/m
24
ng/m3 0.46
ng/m3 4.8
SP1 Mg g/m3 0.051
SP1 Al g/m3 0.25
SP1 Ca g/m3 0.38
SP1 K g/m3 0.43
SP1 Fe g/m3 0.15
16
SP1 Ti ng/m3
SP1 V ng/m3 0.77
SP1 Cr ng/m3 4.2
SP1 Mn ng/m3 6.5
SP1 Ni ng/m3 3.7
SP1 Cu ng/m3 6.0
21
SP1 Zn ng/m3
3
0.29
SP1 As ng/m
SP1 Pb ng/m3 9.5
0.27
0.31
0.49
0.42
0.17
n.d.
3.7
5.5
5.0
5.9
12
17
0.46
12
0.27
0.27
0.43
0.27
0.15
n.d.
3.6
2.2
n.d.
3.2
5.7
13
0.45
11
0.050 0.051
0.26 0.26
0.39 0.42
0.41 0.32
0.087 0.13
n.d.
n.d.
0.32 0.94
5.8
3.8
5.4
5.6
4.3
2.8
3.5
3.7
16
12
0.35 0.20
8.6
4.7
SP2 Mg g/m3 0.050
SP2 Al g/m3 0.29
SP2 Ca g/m3 n.d.
SP2 K g/m3 0.53
SP2 Fe g/m3 0.18
SP2 Ti ng/m3 5.1
SP2 V ng/m3 0.97
SP2 Cr ng/m3 4.2
SP2 Mn ng/m3 4.5
SP2 Ni ng/m3 3.9
SP2 Cu ng/m3 7.4
SP2 Zn ng/m3
27
3
SP2 As ng/m
0.34
3
SP2 Pb ng/m
11
0.044 0.050 0.052
0.28 0.33 0.25
0.28 0.62 0.12
0.91
1.3
0.93
0.27 0.36 0.24
10
12
8.3
0.89
1.9
1.6
8.9
9.3
8.8
7.9
8.8
5.3
8.1
7.1
5.4
13
13
11
38
53
30
0.67 0.85 0.76
18
19
18
0.11
0.24
n.d.
0.059 0.089 0.033 0.034
0.14 0.22 0.32 0.22
n.d.
n.d.
n.d.
n.d.
0.41
0.56
5.9
4.9
0.75
4.5
3.1
1.7
16
0.47
1.0
0.42
0.11
n.d.
1.3
n.d.
1.5
1.7
3.3
12
0.28
n.d.
0.54
0.16
2.9
1.9
0.50
2.3
2.2
4.6
15
0.41
8.0
0.50
0.11
3.7
0.48
5.3
3.7
3.3
3.5
21
0.33
7.9
0.37
0.15
4.4
0.64
3.8
3.5
3.0
4.9
17
0.21
n.d.
0.064
0.49
0.54
0.73
0.29
21
1.1
8.3
8.4
4.8
13
30
0.41
7.8
Mg
0.35
0.30
Al
0.7
SP1
ML
SP2
0.6
0.5
g/m3
g/m3
0.25
SP1
ML
SP2
0.20
0.4
0.15
0.3
0.10
0.2
0.05
0.1
0.00
0.0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
K
Ca
1.6
1.4
1.4
SP1
ML
SP2
1.2
1.0
1.0
g/m3
g/m3
1.2
SP1
ML
SP2
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
Ti
Fe
0.6
0.5
25
SP1
ML
SP2
SP1
ML
SP2
20
ng/m3
g/m3
0.4
0.3
15
10
0.2
5
0.1
0.0
0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
Figure 10: Comparison of the results obtained by SP1, ML and SP1 in the analysis of some elements
v
6
Cr
14
SP1
ML
SP2
5
12
SP1
ML
SP2
10
ng/m3
ng/m3
4
3
8
6
2
4
1
2
0
0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
Mn
12
10
Ni
9
SP1
ML
SP2
8
SP1
ML
SP2
7
6
ng/m3
ng/m3
8
6
5
4
4
3
2
2
1
0
0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
Cu
18
16
Zn
60
SP1
ML
SP2
50
SP1
ML
SP2
14
40
ng/m3
ng/m3
12
10
30
8
6
20
4
10
2
0
0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
Pb
As
1.2
1.0
35
SP1
ML
SP2
30
SP1
ML
SP2
25
ng/m3
ng/m3
0.8
20
0.6
15
0.4
10
0.2
5
0
0.0
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
dec 11 dec 12 dec 13 dec 14 dec 15 dec 16 dec 17 dec 18 dec 19 dec 20
Figure 11: Comparison of the results obtained by SP1, ML and SP1 in the analysis of some elements.
In general, the three time series show similar time patterns, and a moderate agreement
was obtained for all elements. The best results were obtained for potassium and zinc: the
average per cent differences of each series with respect to the average of the three
determinations was between 3.1% (ML) and 8.5% (SP1) in the case of potassium and between
6.5% (ML) and 13.8% (SP2) in the case of zinc. In some cases the results were worsened by
the presence of possible outliers. For example, in the case of iron, SP2 result for December
16th was clearly in excess: by eliminating this value, the per cent difference of SP2 results for
iron with respect to the average of the three determinations improved from 29.6% to 4.9%.
The results of the linear regression between the three possible pairs of datasets are
reported in Table VII. A very good agreement is obtained by all three groups for the analysis
of Zn (Pearson’s coefficient in all cases higher than 0.8). When considering only SP2 and ML,
four more elements (Ca, K, Ti, As) show a Pearson’s coefficient better than 0.9; when
comparing SP2 and SP1 a value of R2>0.9 is obtained for one more element only (Cr); no more
good correlations are found when considering SP1 and ML. Again, when eliminating the
outliers the situation improves; for example, by eliminating the Fe value recorded by SP2 on
December 16th, the correlation for Fe of SP2 with ML and SP1 increases to 0.94 and 0.78,
respectively. In these conditions, the average correlation for the 14 elements is 0.70 for SP2
vs. ML, 0.54 for SP2 vs. SP1 and 0.61 for SP1 vs. Ml..
For many elements, the time series of the groups (SP1 and ML, SP2 and ML) that
employed different analytical techniques (ICP and XRF, respectively) are in better agreement
than the two time series obtained by the two groups using the same technique (SP1 and SP2).
This is particularly true for Ca, Ni, Cu, Zn, As, Pb, while only in the case of Cr the agreement of
the two groups using the same technique is the best one.
Table VII: Pearson’s coefficient (R2) for the pairs of datasets in winter inter-comparison
ELEMENT
SP2 vs. ML
SP2 vs. SP1
SP1 vs. ML
Mg
Al
Ca
K
Fe
Ti
V
Cr
Mn
Ni
Cu
Zn
As
Pb
0.16
0.31
0.73
0.46
0.32
0.18
0.99
0.43
0.59
0.96
0.80
0.69
0.02
0.01
0.84
0.90
0.49
0.27
0.38
0.40
0.67
0.87
0.96
0.69
0.81
0.70
0.44
0.39
0.33
0.52
0.77
0.46
0.54
0.95
0.88
0.95
0.97
0.76
0.86
0.23
0.01
0.53
Determination of EC and OC: summer inter-comparison
In this case we had five participating groups. To evaluate the performance of the results
we calculated the consensus values from participants, by following the procedure reported in
ISO guides 5725 and 13528.
The consensus values and the results obtained by the five groups for Organic and
Elemental Carbon analysis are reported in Tables VIII and IX, together with the results of the
regression analysis between the data series of each participant and the consensus values. The
same data are also reported in Figures 12 and 13.
Table VIII: Measured concentrations and consensus values for Organic Carbon (g/m3)
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
R2
intecept
slope
ER
GR
SP2
ML
SP1
5.0
5.6
10
7.4
5.9
8.2
7.9
7.5
4.9
4.6
0.18
4.3
0.27
4.8
4.5
5.5
6.5
11.1
5.5
4.4
7.1
4.9
5.6
0.54
3.5
0.43
4.2
4.7
6.5
8.2
8.7
8.82
5.6
11.1
6.1
5.4
0.77
2.9
0.46
4.8
3.9
5.0
7.6
7.8
7.1
6.3
6.5
5.5
6.0
0.84
0.98
0.84
3.8
4.2
4.7
6.1
5.5
5.2
6.4
6.3
5.4
4.5
0.55
1.2
0.94
consensus value
4.7
4.5
5.8
7.1
7.8
7.0
6.2
7.2
5.4
5.2
Table IX: Measured concentrations and consensus values for Elemental Carbon (g/m3)
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
R2
intecept
slope
ER
GR
SP2
ML
SP1
consensus value
1.6
1.3
1.6
1.2
1.3
1.6
1.2
0.99
0.96
0.61
0.23
1.5
-0.39
0.42
0.55
0.63
0.87
1.6
0.77
0.69
0.98
0.89
0.88
0.54
0.50
0.61
0.36
0.53
0.88
1.2
0.98
1.1
1.1
1.5
1.2
1.3
0.83
0.27
0.74
0.33
0.41
0.50
1.2
1.3
1.2
1.0
1.3
1.5
1.2
0.85
0.41
0.59
0.52
0.81
0.93
1.4
1.1
1.2
0.98
1.3
1.2
1.4
0.80
0.03
0.92
0.45
0.63
0.88
1.2
1.2
1.2
1.0
1.2
1.1
1.1
As expected, these data show that the determination of EC and OC is critical, particularly
when different thermal protocols are used. The series of results provided by ER, which is the
only group to use the EUSAAR_2 protocol, shows, in fact, quite different EC results from the
other groups. EUSAAR_2 differs from the NIOSH QUARTZ protocol for the maximum
temperature of the He step (650 °C instead of 870 °C). In these conditions a incomplete
evolution of OC during the first phase of the analysis may occur, causing a underestimation of
OC and overestimation of EC.
ORGANIC CARBON
12
10
g/m3
8
6
4
2
ER
GR
SP2
ML
SP1
CONSENSUS VALUE
0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
Figure 12: Comparison of the results obtained in the analysis of OC in winter inter-comparison
ELEMENTAL CARBON
1.8
1.6
1.4
g/m3
1.2
1.0
0.8
0.6
0.4
Figure 8: Comparison of the results
obtained inGRthe analysis of OC and EC.
ER
0.2
SP2
ML
SP1
CONSENSUS VALUE
0.0
jul 24
jul 25
jul 26
jul 27
jul 28
jul 29
jul 30
aug 1
aug 2
aug 3
Figure 13: Comparison of the results obtained in the analysis of EC in winter inter-comparison
Determination of EC and OC : winter inter-comparison
The consensus values and the results obtained by the five groups performing Organic
and Elemental Carbon analyses are reported in Tables X and XI, together with the results of
the regression analysis between the data series of each participant and the consensus values.
The same data are also reported in Figures 14 and 15.
Table X: Measured concentrations and consensus values for Organic Carbon (g/m3)
dec 11
dec 12
dec 13
dec 14
dec 15
dec 16
dec 17
dec 18
dec 19
dec 20
R2
intecept
slope
ER
GR
SP2
ML
SP1
8.0
13
20
14
6.8
7.5
7.5
7.1
5.3
9.1
0.998
0.17
0.92
6.6
11
18
11
5.7
6.7
7.0
5.8
4.5
7.5
0.985
0.91
0.98
12
19
30
21
10
12
11
11
8.2
15
0.989
0.30
0.60
7.9
13
18
12
6.1
7.2
7.3
7.1
5.2
9.1
0.991
-0.40
1.03
7.6
12
18
13
6.8
7.5
7.2
6.6
5.1
8.2
0.996
-0.46
1.05
consensus value
7.5
12
18
13
6.3
7.2
7.3
6.6
5.0
8.5
Table XI: Measured concentrations and consensus values for Elemental Carbon (g/m3)
ER
dec 11
dec 12
dec 13
dec 14
dec 15
dec 16
dec 17
dec 18
dec 19
dec 20
2.0
3.3
3.5
3.1
1.1
1.4
1.6
0.98
0.97
2.3
0.955
R2
intecept 0.0.73
0.91
slope
GR
SP2
ML
SP1
consensus value
1.8
2.8
3.7
2.5
0.91
1.4
1.6
1.0
0.86
2.0
0.991
0.100
0.98
2.1
3.8
4.9
3.5
1.5
2.0
2.4
1.1
1.1
2.7
0.964
0.12
0.72
2.1
2.5
3.6
2.6
1.3
1.5
1.7
1.3
0.75
1.8
0.963
-0.15
1.09
1.8
2.8
3.9
2.7
1.0
1.4
1.4
1.1
0.90
1.9
0.991
0.14
0.94
1.9
2.9
3.7
2.7
1.1
1.4
1.6
1.1
0.87
2.0
ORGANIC CARBON
35
30
ER
GR
SP2
ML
SP1
CONSENSUS VALUE
g/m3
25
20
15
10
5
0
dec 11 dec 12
dec 13
dec 14
dec 15
dec 16
dec 17 dec 18
dec 19
dec 20
Figure 14: Comparison of the results obtained in the analysis of OC in winter inter-comparison.
ELEMENTAL CARBON
6
5
ER
GR
SP2
ML
SP1
CONSESUS VALUE
g/m3
4
3
2
1
0
dec 11
dec 12
dec 13
dec 14
dec 15
dec 16
dec 17
dec 18
dec 19
dec 20
Figure 15: Comparison of the results obtained in the analysis of EC in winter inter-comparison.
During the period of the winter inter-comparison, OC and EC values were much higher
than during the summer; in these conditions, the results of the inter-comparison were much
more consistent. The results of the regression analysis between each data set and the
consensus value, in fact, yield R2 values higher than 0.9 in all cases. However, ER, SP1, GR and
ML groups show satisfactory values also for the intercept and slope, while the values of the
slope for SP2 were significantly lower for both OC and EC.
CONCLUSIONS
The results of the summer and winter inter-comparison exercises carried out in the
framework of the MED-PARTICLES project highlighted the difficulties that can be
encountered when comparing analytical data obtained by different laboratories during
different time periods.
During both exercises it was not possible to detect systematic errors; the differences
among the series of data yielded by the participants were generally dependent on the
particular set of analyses. For example, the results yielded for ammonium by ML and GR
groups were similar during the summer period while a systematic bias (ML > GR) was
detected during the winter period.
In general, during both periods the best agreement was obtained for sulphate analyzed
by IC. Elements showed more variable results: the best agreement was found for V and Fe
during the summer period and for K and Zn during the winter period. When considering the
participating groups, the best agreement in the elemental analysis was obtained, during both
periods, by SP2 and ML, in spite of the different analytical techniques employed (ICP and XRF,
respectively).
The results for EC and OC determination were much more satisfactory during the winter
inter-comparison, characterized by much higher concentration. During this period a very
good agreement was observed among all groups, with a systematic positive bias for SP2.
During the summer period, instead, more variable results were obtained by all groups; the
values from the ER group were even more different, probably because of the different thermal
protocol used.
Given their non-systematic nature, the results of these inter-comparisons cannot be
used to correct the datasets of the MED-PARTICLES project. For the future, the findings of this
exercise suggest the need for a centralized laboratory taking care of the analyses from all the
sampling stations, or, in alternative, the necessity to run frequent inter-comparison in the
course of the periods when the analytical work is carried out.