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Technical Note (National Research Council of Canada. Division of Building Research), 1971-07-01
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Comparison of Measurements of Atmospheric Sulfur Dioxide by the
Sulfation Plate and Cylinder Methods
Ritchie, T.
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DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
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'fE
C
1HI !if ][ CAlL
NOTlE
No.
561
PREPARED BY T. Ritchie CHECKED BY PJS APPROVED BY NBH
July, 1971
PREPARED FOR . Record Purposes
SUBJECT COMPARISON OF MEASUREMENTS OF ATMOSPHERIC SULFUR DIOXIDE BY THE SULFATION PLATE AND CYLINDER METHODS
As part of DBRts.program for the study of metal corrosion,
measurements have been made for many years of the an10unt of 502 in
the air at several exposure sites. The method involves exposure to the
air (in a louvred box) of a porcelain cylinder to which a gauze
impreg-nated with lead peroxide has been applied. This material, which reacts
with S02 in the air, is analysed following a one-month period of exposure
of the cylinder and provides a measure of the 502 content of the air for
that month. Details of the method are given in NRC 4758.
A similar method of monitoring atmospheric SO." the Huey
Sulfation Plate method, also employs an 502 -reactant material, but it
is attached to a plane circular surface of about 2 -in. diameter. This
plate is mounted on a bracket with the surface of the reactant material
face down in the horizontal plane. The sulfation plate method of
monitor-ing ｓｏｾ is available on a commercial basis from Corning Laboratories,
Inc. ,Cedar Falls, Iowa, U. S. A., which sells plates to customers f01'
exposure and subsequent return for analysis. Because of the possible
advantages of monitoring 502 by the commercial ｳｵｾｦ｡ｴｩｯｮ plate method,
a comparison was made of the relative costs of the DBR and commercial methods and of the results obtained by each .
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2
-COST
In preparing cylinders for exposure and analysis, the following time is required by the technician responsible for the various phases of the work: ( a ) ( b ) ( c ) ( d ) ( e ) ( f )
Preparing cylinders ( stitching gauze and applying lead peroxide paste)
Stripping cylinders and initial treatment of gauze Processing lead peroxide for analysis ( boil, filter, wash, acidify, precipitate)
Final processing ( filter, wash, ignite, weigh) Calculate results
Clean glassware and equipment Total Time 1.z hr 3 hr 1.z hr I hr 11 hr
The required time of 11 hr applies to the processing of 10
cylinders. At an hourly rate of $5. (used by DBR for technician costs
the work is valued at $55., exclusive of the cost of materials and
chemicals ( gauze, lead peroxide, solutions for analysis, etc. ); this
is estimated at $5. The total cost of processing 10 cylinders is thus
$60.
Corning Laboratories Inc. has supplied DBR with sulfation plates
at a cost of $30. 50 for 20, and has analysed them for $3. 10 each. Based
on 10 plates ( corresponding to the 10 cylinders described previously)
the costs charged by Corning Laboratories were $15.25 for the plates
and $31. for the"analysis, for a total of $46.25 (U.S. funds). Assuming
5 per cent premium on U. S. funds the cost becomes $48.56, compared with
$60. for work done by DBR. COMPARISON OF RESULTS
A sulfation plate, attached to a bracket on the louvred box holding the cylinder, was exposed over the same period of time as the cylinder.
Such duplicate measurements were made at the e'i>osure sites in
Halifax and Ottawa, monthly measurements of S02 being made in the
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-A comparison of the measurements obtained at the same location
by the two methods for the same month of exposure (Figure I ) showed
that at relatively low values of SOa (which by. convention is expressed
as milligrams of SOs per 100 sq cm per day) the two methods gave
comparable results, although there was considerable scatter of results
from the line of equal values. At relatively high values of SOs the
cylinder method produced higher values than the plate method. REPRODUCIBILITY OF RESULTS
Three cylinders, each in a louvred box, and three plates, one attached to a bracket on each box, were exposed at Ottawa over the
same period of time. The following table indicates less variability for
the plate method than for the cylinder method.
S03 (mg/IOO cma/day)
Sample By By
No. Plate Method Cylinder Method
1 0.34 0.34
2 0.39 0.46
3 0.39 0.48
Ave. 0.37 0.43
CONCLUSIONS
The measurement of atmospheric SOa can be carried out more cheaply by using sulfation plates and analysis provided by Corning Laboratories Inc. than by the cylinder method now employed by DBR.
The results obtained by the two methods are comparable for
values of SOs below 0.7 milligrams per 100 sq cm per day; above
this value the cylinder method produces higher figures than the plate
method. It should be noted, however, that the plane of exposure of
the S02 -r eactant material, as well as its size and shape, differ s in the two methods and may account for the differences in results.
