A comparison of summer and winter fallout of sodium sulphate near a kraft mill

Atmospheric Environment Pergamon Press 1972. Vol. 6, pp. 947-948. Printed in Great Britain.

SHORT COMMUNICATION A COMPARISON OF SUMMER AND WINTER FALLOUT OF SODIUM SULPHATE NEAR A KRAFT MILL (First received 29 January 1972 and in final form 12 June 1972) A&tract-The fallout of sodium sulphate as a function of distance from a kraft mill obtained during the summer is compared to that obtained during the winter. THROUGHOUTthe fall and winter of 1970/71 snow was used to determine the rate of fallout of sodium sulphate as a function of distance from a kraft mill in Thunder Bay, Ontario (HASTINGSet al., 1972).

In order to corroborate the winter data, and to obtain a fallout profile for the summer months the study was continued to September 1971. FIGURE 1 is a composite plot of the accumulated concentration of SOa2- in mg m-2 vs distance in yards due east of the mill. The data points represent SOd2- ion concentration and were obtained by analysing ram water collected from polyethylene lined tubs. The numbers to the left of the curves indicate elapsed weeks from the initiation of the study (15 May 1971). Curves connecting the points separate one week from the other. The fallout predicted by the winter study for a fifteen week period is indicated by the large discs. In an effort to reduce the effects of possible contamination the tubs were emptied and liners changed after the seventh and twelfth weeks of the study.

. 4000

l Winter 1971-72 0 Summer 1972

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FIG. 1. The accumulated

concentration of SOd2- as a function of distance from a kraft mill. The summer data corresponds to analyses made at the week indicated to the left. The winter data is that predicted by a previous study for a H-week period. 947

948

Short Communication

FIGURE 1 indicates in some detail the evolution of the summer fallout profile. It is apparent that distribution of fallout is not a simple function of distance from the mill. For example the distribution changes from one with a single peak at a distance of 1200 yd from the mill in early June, to an apparem bimodal distribution in September with one peak within 900 yd of the mill and one beyond 2700 yd. The detailed nature of the fallout distribution depends upon variables such as particle size of airborne sodium sulphate and the temporal correlation between the emission of it with wind velocity and direction, and rain. An attempt was made to determine the weekly changes in the curves by assuming a constant rate of emission in relation to hourly variations in wind direction and velocity, and rainfall. It was concluded that few complementary weekly correlations were obtained due to lack of specific information concerning the short term changes in the emission rate. A comparison of the winter and summer distributions in fallout indicates that they are similar tn shape and magnitude (FIG. 1). Differences may be attributed to meteorological factors. In conclusion the fallout rate near the kraft mill is appreciable: roughly 10 g S0,2w m-’ yr-’ at 1500 yd. Lakehead Utzicersit~~ Thunder Bay Ontario, Canada

L. HASTINGS* R. FREtTACit

REFERENCES HASTINGSL., FREITAGR. and SMITHA. (1972) Fallout of sodium sulphate near a kraft mill. Atmospheric Environment 6, 241-246.

* Department t Department

of Physics. of Biology.