LRTAP-16-75.pdf (1.659Mb)

LRTAP-16/75

REMARKS ON THE QUALITY OF THE LRTAP GROUND SAMPLING DATA

BY

J, SCHAUG, A. ^{SEMB AND} F. ^GRAM

KJELLER, 21ST MAY 1975

NORWEGIAN INSTITUTE FOR AIR RESEARCH P.O. BOX 115, 2007 KJELLER

NORWAY

CONTENTS

INTRODUC'l¹ION . . . 5

ANALYSIS OF STANDARD SAMPLES AND

EXCHANGE OF SAMPLES . . . 7

COMPARISON WITH OTHER SAMPLING

AND ANALYSIS METHODS . . . 8

CORRELATION BETWEEN NEIGHBOURING STATIONS . 9

CONCLUSIONS . . . 10

Sulphate in precipitation 10

Strong acid in precipitation . . . 11

E.!! . • • . . • . • . • • . . . . • . . • • . . • . • . . . . • . • . • . • • • • . . . • • . • . .

11

Sulphate collected on filter 11

Sulphur dioxide . . . • . . . 12

REFERENCES . . . 13

- 5 -

INTRODUCTION

In addition to the collection and edition of the results from the ground sampling network, the CCU has been respon- sible for the distribution of standard procedures for

sampling and chemical analysis (1-6), and for testing of the methods through distribution of standards and exchange of

samples. Results of the intercalibration and other tests giving information on the p ro c i s i.on and accuracy of the

methods, as well as more general remarks on the data quality are given in the following.

ANALYSIS OF STANDARD SAMPLES AND EXCHANGE OF SAMPLES

A serie of synthetic standard samples have been circulated to the participating countries for testing of the precision of the methods. Results from the collaborative testing are presented in Table I, also presented in the table are the mean values and the dispersion of the· results expressed by the root mean square deviation.

While the dispersions of the sulphate data (- "in preci- pitation") are nearly constant and independent of the added amount of sulphate, the dispersions of the sulphur dioxide and the strong acid results are more variable. The analyses were run in the preparatory phase of the project and several of the laboratories had limited practical experiences in the application of these particular methods.

Table II gives results of a ·comparative test using several different methods. These were: X-ray fluorescence (7), isotope dilution (IDA) (8), Wickbold nephelometric method

(9), and the' results are given with the added amount of sulphur as sulphate. The results from five precipitation samples using the same three methods and in addition the Thorin method are also included.

Several filters from air samples have been distributed among the participants and analysed by the XRF-method at different laboratories. Table III gives the XRF results of filters from 1974 exposed at the Austrian stations and analysed at Bundesstaatliche Bakteriologisch-serologische Untersuchungsanstalt in Austria by XRF and at the Norwegian Institute for Air Research (NILU) by the Thorin method.

Table IV gives corresponding results analysed by XRF at Warren Spring Laboratory and at the Norwegian Institute for Atomic Energy (IF'A) .

Warren Spring Laboratory has found out that plots of chemi- cally determined sulphate concentrations versus the X-ray count follows a straight line when IB/IF exceeds 0.2. When the IB/IF ratio is lower than 0.2 the slope of the curve is no longer independent of IB/IF and if a linear relation is assumed an error may be introduced. However, the errors intro- duced by this assumption are probably of little practical

importance as Figure 1 shows.

A number of precipitation samples have been exhanged between the participating laboratories. Table V gives the results of Dutch samples analysed at RIV and NILU and British samples analysed at WSL and NILU. Some of the discrepancies may be due to storage effects, as these samples were analysed the second time about 4-6 weeks after the sampling.

COMPARISON WITH 0'.f.'HER SAMPLING AND ANALYSIS fvIET!:IODS

The Rijksinstitut vor de Volksgesundheit (RIV) in the Nether- lands ran a comparison of the tetrachlotomercurate and the Thorin method at the three stations Wageningen, Witteven and den Helder in 1972-1973. Table VI compares the TCM method which is specific for sulphur dioxide and the Tho:r:in method which gives the total gaseous sulphur, which can be oxidi7.ed

to sulphate in an hydrogcnperoxide solution at pH 5. The Thorin method gives, as may be expected, generally higher mean

concentrations and maximum values. The slope of the regression lines are probably not significantly different from 1.0,

indicating that the methods give nearly identical results when considering possible interferences (e.g. by ozone in the TCM method) .

The advanced sampling programme sulphate aerosol con- centrations are determined using a wet chemical method.

Figure 1 presents corresponding results from the NORDFORSK project in 1973. The results are in very good agreement, it might seem as if the wet chemical method has a tendency to give slightly higher results.

This may be due to a more efficient collection of larger particles by the high ·volume sampler.

CORRELATION BETWEEN NEIGHBOURING STATIONS

The correlations obtained between observed and predicted values are limited by several noise factors.

For sulphur dioxide the measurements are probably no better than± 3-5 µg SO₂/m³• Also the observations are log-nor~ally distributed, so that the correlation is determined by a few observations (episodes). The corre- lation coefficients therefore depend on the number of observations and the observation period. Contamination errors and spurious influence from local sources may reduce the correlation seriously.

Two of the stations in Norway are sufficiently close to warrant an investigation of the mutual correlation. The correlation in the daily SO₂ values for the months January- June 1974 was 0.540 : the standard deviation in the same period± 9.1 µg SO2/m³• There was, however, at least two cases of strong deviations: 2nd January with 29 µg SO2 at N0l, 1 µg/m³ at N03. 17th March N0l had 6 µg/m³, while

N03 reported 80 µg/m^3• 3rd January and 16th March gave high

- 10

observations at both stations, but the value 80 µg/m³ is pro- bably an error. When these two observation pairs are left out, however, the standard deviation becomes± 5.4 µg/m³,

which compares favourably with the estimated precision of '\., 3 µg SO2/m³ (3/2::; 4.2).

The correlation is increased to 0.726.

The spacing of the gr_ound sampling stations is not sufficient- ly dense to allow rejection of similar "accidents" from the data on a general basis.

Because of this, calculated correlation coefficients between observed and estimated, and between neighbouring stations cannot be directly interpreted. Some qualitative information may be obtained from a comparison of space correlation coeffi- cients for SO2 and SOi;, as for example in Figure 2 and 3.

(The values are listed in Tables VII and VIII.) It is

seen that the calculated correlation coeffj.cients are highest for neighbouring stations and for the stations where long range transport is expected to contribute most significantly to the observed SO₂ and sulphate concentrations.

It may also be of interest to compare correlations between neighbouring stations with correlations between observed and estimated values, for identical sets of observation data.

CONCLUSIONS

Sulphate in precipitation

The precision of the chemical analysis is believed to be close to 0.2 µg/ml, from the results presented in Table I, and considering the improvement in laboratory performance during the programme.

_____

^,;

Strong acid in precipitation

The accuracy in this parameter has earlier been found to be accurate to the nearest 5 µeq/1. It seems that storage in polyethylene bottles seems to increase the strong acid concentration slightly.

The storage effect mentioned above will of course also have an effect on the measured pH-values. These pH-

values found at NILU in the Austrian samples are generally lower than the corresponding Austrian results, the

difference in the British samples are less and the agree- ment is better. This corresponds with the measured acid

concentrations in the Austrian and British samples. There is generally good agreement between measured pH and strong acid concentrations, when pH< 5.5 (Table IX).

Sulphate collected on filter

Calibration of the XRF -results by wet chemical analysis using filters impregnated with sulphate in aqueous solutions as secondary standards has shown that the absorption of X-rays in the filter material and variations of the penetration depth of the particle samples does not have serious effects on the results. A constant factor may be used to obtain the amount of sulphate on the filters (10, 11).

It has been pointed out that wetting of the filters may intro- duce errors up to 50%. Subsequent wet chemical determination of sulphate was carried out in connection with the testing of the XRF method in the preparatorj phase (10), and has since been repeated for a set of filters from Austria

(Table III). The agreement is partly limited by the precision in the wet chemical analysis method.

- 12 -

When XRF has been used to determ ine sulphate on the same filters at different laboratories, the agreement has generally been good.

The comparison between the wet chemical method during the

NORD FORSK 100-day period, and the XRF-method gives a generally 15% lower XRF-result, the difference probably due to different collection efficiency for the large particles.

Sulphur dioxide

The minimum detectable sulphur dioxide concentration is around 2-5 µg/m³• The dispersion between the concentration values presented in Table 1 is small, the relative standard error is less than 5% for the sample above the detection limit.

Several frequency distributions of sulphur dioxide concen- trations are presented (Figure 4-7).

A quantization effect may appear in the data due to a tr~ncation which will occur in the computation of the

air concentrations from the analysis results in the labora- tories. This will be up to 2-5 µg/m³ (Figure 4) ~

Because of noise in the analytical signal, Qnd because

spurious positivG readings near the detection limit are not balanced with corresponding negative readings, the mean values will in general be somewhat positive biased. This error will be a fraction of the detection limit, and will occur only if a significant percentage of the daily con- centrations are below the detection limit.

More serious truncation errors are revealed in Figures 6 and 7. These errors have been eliminated through a change in laboratory practices.

There has also been a change in the analytical methods for

the German stations. This change occurred in February-March 1974.

REFERENCES

( 1) Central Coordinating Unit, Norwegian

Institute for Air Research

( 2) Central Coordinating Unit, Norwegian

Institute for Air Research

( 3) Central Coordinating Unit, Norwegian

Institute for Air Research

( 4) Central Coordinating Unit, Norwegian

Institute for Air Research

( 5) Central Coordinating Unit, Norwegian

Institute for Air Research

( 6) Central Coordinating Unit, Norwegian

Institute for Air Research

Spectrophotometric deter- mination of sulphate by the barium perchlorate-Thorin method.

Determination of sulphur dioxide in air and sulphate in precipitation.

LRTAP-4/71, September 1971.

Coulometric titration of strong acid in precipi- tation.

LRTAP-5/71, September 1971.

Determination of sulphur dioxide in air and airborne sulphate in the particulate phase.

LRTAP-2/72, July 1972.

Determination of strong acid and sulphate in precipitation.

LRTAP-3/72, July 1972.

Determination of particulate sulphur collected on Whatman 40 air filters by X-ray

fluorescence.

LRTAP-4/72, July 1972.

Reporting and distribution of results.

LRTAP-6/7~, July 1972.

- 14 -

(7) G. Ronicke

(8) D. Klockow:

H. Denzinger, G. Ronicke

(9) R. Wickbold

(10) M. Bonnevie-Svendsen, A. Follo

(11) P. Grennfelt

Flilssigkeitsuntersuchung mit der Rontgen-Fluoreszenzanalyse.

Analysentechnische Mitteilungen Nr 12, Juni 1972, Siemens A-G.

Gewendung der Substochiomet- rischen Isotopenverdilnnings- analyse auf die Bestimrnung von atmospharischern Sulfat und Chlorid Ln "Background"-Luft.

Chemie-Ingenieur-Technik, .i§_,

831 (1974). -

Die photornetrische Trlibungs- titration zur Bestimmung kleinster Sulfatrnengen.

Angew. Chern., 65, 159 (1953).

Evaluation of filters , stand- ardization and næasuring proce- dures for X-ray fluorescence analysis of sulfur in airborne matter.

Work report CH-98,

Norwegian Institute for Atomic Energy, Kjeller, June 1972.

Comparative measurements of particle-borne sulphur by X-ray fluorescence and of soot by reflectance, using different filler materials.

IVL Report B 133.

Swedish Waler arn.1 Ai.r: Pollution Research Laboratory,

Gothenburg, November 1972.

L.

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Wet chemical analysis

FIGURE 1: Comparison of results by X-ray fluor- escence on filters from an OECD-type sampling apparatus with wet chemical

analysis of high-volume samples collected on Acropor-5000 filters.

May - June 1973.

- 16 -·

0

7

FIGURE 2: Correlation between measured daily sulphur dioxlde concentrations at neighbouring stations.

FIGURE 3: Correlation between measured daily sulphate aerosol concentiations at neighbouring stations.

- 18 - JOl\1011\J[r-l SF 2

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Oct - Dec 73

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^{S02 SO,f 2-} PRECIPITATION

I

^{Number I II III IV V} ·-· ^{VI VH VIII XI X l 4 6 17 31}

Added

0.6 2.8 l. 7 9.5 0.3 3.6 1.3 1.9 2.6 1.8

I

_c.mount ^-

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^-

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XRF 0.6 2.8 1.8 7.2 0.5 4.0 2.1 1.3 2.3 l. 7 l. 7 0.7 1.4 0.3 0.7

ID 0.5 2.8 1.8 10.l 0.6 3.6 l. 3 l. 7 2.6 1.8 1.6 0.7 1.4 0.3 0.8

Wb 0.9 2.6 1.7 6.3 0.7 2.6 1.2 1.1 1.5 0.9 0.9 0.5 0.9 0.6 0.6

---

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^{- - - 1.6 0.7 1.6 0.3 0.9}

'

TABLE II: Comparison of different methods for deterrning sulphur.

All figures in mg S/1.

XRF: X-ray fluorescence analysis

(Deutsche Forschungsgemeinschaft) ID:

Wb:

Isotopic dilution analysis

(Deutsche Forschungsgemeinschaft) Wickbold nephelometric method

(Deutsche Forschungsgemeinschaft) Thorin: Thorin method (NlLU)

- 23 -

-·

Filter XRF THORIN

THORIN/XRF µg SOtJfilter µg S04/lO ml

1/2-74 61.05 34.50 0.56

2/2 37.80 28.50 0.75

3/2 48.80 33.00 0.67

4/2 18.05 18.00 0.99

5/2 18. 71 14.25 0.76

2/3 32.08 18.00 0.56

3/3 32.60 20.70 0.63

4/3 ^{39.55 27.75 0.70}

5/3 22.24 19.50 0.87

6/3 47.84 34.20 0.71

1/4 14.4 16.20 1.12

2/4 17.34 16.20 0.93

3/4 13 .89 11.25 0.80

4/4 13. 93 12.00 0.86

5/4 23.44 17.70 0.75

Mean weighted factor Mean factor

Standard deviation

THORIN/XRF: 0.72

II 0. Tl

±0 .14 (18%) (Relative error in THORIN determination:< 10%)

TABLE III: Comparison of the THORIN and the XRF methods. The filters are exposed at

Illmitz.

UK Results N Results

Date Station

]Jg S04/4.9 en/ IB/IF ^]Jg SOif/4 .9 cm² 113/IF

721213 Cottered 13 .19 11.5 .22

28 " ^fl 19 .22 16.8 .24

730119 " ^{fl 56 .07 75.0 .10}

24 ^fl " ^{30 .07 37.8 .09}

' ₁₇ Eskdalemuir 4 .23 2.4 .04

20 ^li " ^{11 .19 9.3 .18}

29 Cottered 19 .11 18.9 .15

24 Eskdalemuir 9 ~og 10.3 .12

26 ^fl " ^{7.5 .25 5.9 .20 I}

30 ^II " ^{3 .07 3.1 .11}

I

TABLE IV: Sulphate on filters, exposed at Cottered and Eskdalemuir.

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- 25 -

Method/Station Observations Mean concentration Maxi.mum Minimum

-

TCM(l) 120 8.27 52.00 0.00

Th ( 2) 120 11.66 62.00 0.00

TCM(2) 119 6.31 30.00 0.00

Th (2) 120 7.37 29.00 0.00

TCM (3) 117 6.77 22.00 0.00

Th (3) 118 8.07 35.00 0.00

Linear regression (least squares):

Th(l) - 1.06 TCM(2) + 2.88 Th(2) 0.83 TCM(2) + 1.48 Th(3) = 1.14 TCM(3) + 0.39

R = ^0.82

R 0.80 R = ^0.83

TABLE VI: ·comparison of the TCM and the Thorin methods at the three Dutch stations.

TCM(l): Sulphur dioxide concentrations as determined by the TCM or West and Gaeke method (NLl).

Th (3): Total gaseous sulphur compound concentration determined by the Thorin method (NL3).

0 .-1 0 .-1

0 :,,: 0 ::,,:

0 ::i 0 ::i

.-1 .-1

·o N N 0 OJ N

0 0 0 0 0 0

0 N (/) 0 0 ^(/)

.-1 .-1

0 m r--- 'Si' 0 0 OJ 'Si'

0 \.0 ^lI) ..:I 0 0 N 1-l

0 0 ..., z ^{0 .-1 \.0} z

.-1 .-1

Ul

0 N m ^{\.0 (Y) 0 .-1 r--- r--- (Y) (l)}

0 .-1 \.0 s::l' ..:I 0 lI) m ^{Ln ..:I} _:::l

0 N 0 "<I' z ^{0 \.0 .-1 r---} z .-l

.-1 s:: .-1 ru

(l) >

(1)

0 0 m ^{(Y) ()'1 N ::;:: 0 r--- .-1} <::!' \..0 N H

0 ^(·) OJ .-1 ""-I' ^,-:i .jJ 0 m ^{OJ (Y) r---- ,.:i·} _·ri

""

0 \.0 ^(Y) .-1 ('l z (l) 0 ro \.0 N \.0 z _{ru r--}

.-1 ..C! .-1 m

s:: ^.-l

Ul ·ri

0 s:!' 0 m co ro ^{.-1 (l) 0 OJ} m ^{r--- \.0 lI) .-1} (l)

0 I.D ^{0 If) <::!'} OJ ..:I :::l ⁰ m ^(Y) m ^{\.0 (Y) ,.:i} _(l) s::

0 \.0 \.0 \.0 0 ^('l z _r--l ⁰ r---- r---- r---- ^~1 1.0 z _{.jJ :::l}

.-1 ru "" ^.-1 ro ^r-:)

:> r-- ,.i::: I

0 \.0 OJ 'Cl' If) 0 m N ^I Nr-f m ₀ lI) <;j' lI) .-1 0 N N ri ~ >1 H 0 'Si' \..0 r---- ..., _{lI) N N 0} ,,, _{<'l 'Si' m} ()'I 0 N

0 ^{(Y) (Y)} .-1 'Si' 0 N z ⁰ _{CJ) (l)} ^{0 (Y) 'Si' 'Si' N lI) (Y)} z ^{::i ro}

Ul ::i

,-1 s:: ^.-1 s::

~::i ~ ro

0 0 .-1 0 .-1 .-1 ('l lI) ()'I r-1 r-:) _{0 lI) N 'Si'} 0 lI) ^(Y) \.0 m ^{r-1 r-:)}

0 0 ^(Y) ro ^{If) 1.0 N tn 0 ·ri I 0 0} ro ^.-1 \.0 N co N 0 ·ri 0 01 r-l ,...J ,-1 0 C'-1 0 ~?i r(j y' I 0 lI) c-1 ^{(Y) (Y)} .-1 0 ^(Y) :z; ro

•CJ :--i rel Ul

.-1 rd ^r-1 s::

4-l ::i 4-l 0

0 \.0 ^(Y) ro ^{(Y) \.0} m ^{\.0 N (Y) 0} s:: 0 'Si' N . \.0 r---- ^{(Y) lI) M (Y) (Y)} 0 ·ri 0 ^(Y) r---- \.0 \.0 <::I' 0 \.0 s;)' 0 ru ^{0 lI)} m ^lI) \.0 \.0 0 OJ lI) 0 .j.J 0 ..., r-1 0 .-1 0 0 N ..., z s:: ^{r-:) 0 lI) lI) N (Y) (Y) N N (Y) z} s:: m

.-1 0 _.-1 0 .jJ

·ri ·ri Ul

~.J Ul ^.jJ

0 0 .-1 01 \.0 0 <::!' r---- \.0 rn .-1 ro s:: ^{0 r--- Cl) m m m N ,.o r---} "1' ,-1 ru s::

0 -s:I' ^{N If) 0} m ^{li) N (',} r---- 0 r-1 0 ⁰ r---- "1' 0 0 lI) m ^{0J 0 lI) 0} r--l ^Q) 0 ^lI) N .-1 N .-1 .-1 0 ('l .-1 z ^{(l) ·ri 0 co Lf) r---- (Y) 'Si' 'Si' N 'Si' (Y) z Q) (l)}

ri H .J..l _.-1 i-.-1 :s:

H rd H .JJ

0-JJ 0 ^(l)

0 OJ OJ OJ OJ ri lI) r---- .-1 ^(Y) lI) in u ^{Ul 0 lI) N} lI) lI) lI) (Y) \.0 '<.1' ^(Y) \.0 1..n

u

^...0

0 ^("') (j) ()) u li) \i) Lil N .-1 N ~ ^{0 0-, ('1 ('1 .-1 ,-j \.0 .-1 \.0 '1' \.0} ~

0 ,-1 0 ri 0 0 N .-1 .-1 ^(Y) 0 Q ⁰ Ln tn ^{tj' I.()} set' ^{lI) lI) N tj' (Y)} Q

.-1 .-1 H

H H

H ^f-l

0 ^(Y) N r---- ^(Y) .-1 co ^{(i\ .-1} m co ^{OJ (Y)} :> ^{0 (Y) OJ N lI) OJ \.0 0 \.0 N r---- \.0 (Y) ,-._}

0 OJ r---- r---- N ri N 0 .-1 ri co 0 ~ ^{0 0 'Si' <::I' ro} <::I' \.0 0 m ^lI) 0) 0 ~ ^V

0 <::I' .-1 0 0 0 0 0 0 ri 0 0 Q

r.r.:i ⁰ co r--- \.0 -;j' r---- ^{(Y) lI) '.,)'} N lI) ^(Y) Q

i:,.:i

,-1 ....:I ^.-1 ....:I

r:Q r:Q

0 ^(Y) <::I' <'1 OJ OJ .-1 'Si' \.0 ^(Y) \.0 N 0 <:j' .-:i:: ₀ m lI) lI) lI) N \.0 m ^{OJ N \.0 .-1 (i\ <::I' .-:i::}

0 0 0 .-1 lI) 0 ^(Y) <::!' ,-J .-1 <:j' 0 ^(Y) 0 E-1 ₀ m ^(Y) r---- ^(Y) co ^,-i m <::I' ^{lI) lI) (Y) (Y)} 0 E-1

u .-1 u .-1 u ^{ri (Y)} N N ri N ri u ^{/....l 0 0 .-1 ri ,-1 .-1 .-1} '1' '1' '1'

u,

0 '1' Q

.-1 .-1

'Sl' ^{(Y) lI)} .-1 ^(Y) m ^{N ,-1 N M 'Si' N .-1 s;j• (Y) lI) ri (Y)} m N .-1 0-1 (Y) 'Si' N ri

0 ~~ ^{000 N} ..:I HHH 0 ~ ⁰ ~ ^:,,: 0 0 0 N ..:I ..:I ..:I H ⁰ ::,,:

Q Q Q zz z z zz zz ^(/) ::i Q Q Q z z z z z z z z ^(/) ::i

- 27 -

Station "Strong acid" Computed acid Number of

pH interval µekv/9, µekv/9, stations

Birkenes -1. 7 6.8 6 (5. 5, 5.0)

II 15.9 17.7 10 (5.0, 4.5)

II 63.6 56.4 33 ( 4. 5, 4.0)

II 143.5 126.0 11 (4.0, 3.5)

Jokioinen 8.8 8.4 5 (5 .5, 5.0)

II 20.3 18.3 15 (5 .0, 4.5)

II 64.7 55.2 21 (4.5, 4. 0)

II 158.8 153.2 4 (4.0, 3.5)

l

^Cot~ered

^-

^{- 0} (5. 5, 5 .0)

31.5 25.1 2 (5.0, 4.5)

II 57.7 59.6 34 (4. 5, 4. 0)

II 147.8 146.6 18 (4.0, 3.5)

TABLE IX: Comparison of mean strong acid concentrations and mean computed acj_d concentrations for different pH intervals.

Period: January-June 1973.