Roderick W. Shaw Environment Canada Halifax, Nova Scotia
There is much evidence in the literature, including previous issues of ES& T, that emissions of air pollution may be transported hundreds or even thousands of kilometers through the atmosphere, often being transformed chemically along the way, and deposited upon receiving surfaces such as forests, soil or bodies of fresh water. Although they may arrive at their destination in concentrations that are often difficult to detect, they may have cumulative and harmful effects upon receptors. If this is shown to be the case-and much work needs yet to be done-then the use of tall stacks may afford only partial protection to the environment. All other factors remaining equal, the environmental effects of the long-range transport of contaminants should increase as the quantities emitted increase. The Europeans, particularly the Scandinavians, have been especially concerned about the occurrence and effects of long-range transport and subsequent deposition of sulfur compounds ( E S & T , September 1978, p 1016). I n Europe, there has been a marked increase in the acidity of precipitation, and its geographical extent. The increase in acid precipitation and aerosol sulfates in Europe has coincided with a substantial increase in emissions of sulfur oxides (SO,) and possibly nitrogen oxides (NO,) in the last twenty-five years. This has been brought about by rapid industrialization and the depletion of suitable hydroelectric generating sites. The greatest acidity, concentrations and deposition of sulfur compounds occurs in the areas of greatest emissions and declines with increasing distance from them. However, certain localized areas such as southern Sca nd i n av i a and Sw i t ze r 1and have greater deposition than would be expected from their distance from the major sources because of greater precipitation brought about by mount ai no u s t e r ra i n . The Scandinavians claim that the increase in acidic precipitation has caused a marked acidification of lakes in Scandinavia, a reduction in the productivity of trout and salmon and a suspected reduction in the productivity of forests. Problems in Atlantic Canada G . E. Likens of Cornell University has shown that a similar phenomenon has been occurring in eastern North 406
Environmental Science & Technology
0013-936X/79/0913-0406$01.00/0
@ 1979 American Chemical Society
America. His maps of precipitation acidity contain no data from the Atlantic provinces of Canada, but the gradients of pH reported in his papers strongly suggest that long-range transport of acid precipitation affects Atlantic Canada. Furthermore, R. E. Munn of the Canadian Atmospheric Environment Service examined standard aviation weather observations, and noticed a remarkable increase in summer haziness in the Atlantic provinces since the mid- 1950’s. Climatologically speaking, the Atlantic provinces lie in the mid-latitude Westerlies, downwind of large, populated areas on the eastern seaboard of the U S . , and the St. Lawrence Valley-Great Lakes region of Canada and the U.S. In the summertime and early autumn, the provinces can be covered by warm, humid air laden with pollutants from eastern North America. As in Europe, there has been a marked increase in SO, and NO, emissions in North America. In Canada in 1972, 62% of the man-made emissions of SO, came from sulfideore smelters and thermal electric generating stations. Sixty-four percent of the total Cancadianemissions of six million metric tons came from the provinces of Ontario and Quebec, which lie immediately upwind of the Atlantic Region, and only one-tenth that fraction came from the Atlantic region. In the high-emission areas of the eastern U S . , the annual emissions of sulfur dioxide are 19 million metric tons per year, of which about 70% come from the combustion of fossil fuels in generating electricity; these emissions are expected to increase substantially ovex the next decade. Sulfur emissicins may increase even more (because of the tendency to use fuels containing a higher percentage of sulfur) unless desulfurization of fuel prior to combustion or of the resulting exhaust gases is carried out. Flue-gas desulfurization ( F G D ) has been controversial both in the U S . and Canada. While FGD is in increasing use in the U S . , it has not been accepted by provincial control agencies and utilities in Canada as a viable method of control.
Documenting long-range transport Apart from routine monitoring networks which have been operating in Canada only since 1975, the examination of the possible long-range transport of air pollution to Atlantic Canada has been through a small number of isolated, short-term studies carried on since the early 1950’s. Owing to the absence of lengthy, uni-
form records, trends cannot be determined, not because of the quality of data, but because of the rapid shortterm fluctuations in precipitation and air quality which must be smoothed out by averaging over a long period to obtain trends. However, the past studies do seem to indicate that there is a substantial atmospheric input of sulfur compounds into Atlantic Canada. Precipitation frequently has a p H of less than 5.6, the value for “clean” precipitation in equilibrium with atmospheric carbon dioxide. Concentrations of sulfate in precipitation are of the order of several milligrams per liter, and the deposition of sulfate by precipitation is several tens of kilograms per hectare per year. These values are similar to those found by an earlier Organization for Economic Development and Cooperation (OECD) Study for Europe.
Study of note One recent study deserves special mention. In the summer of 1976, the Federal Department of the Environment initiated the “Intensive Sulfate Study” in eastern Canada. Some interesting results are shown in Figures 1 to 3, which are maps showing isopleths of concentration of aerosol sulfate (24-h samples) in eastern Canada. The first map, for 12 August 1976, shows high concentrations of sulfate in the St. Lawrence Valley, believed to be the northernmost extension of a large area of high concentrations in the northeastern U.S. This belief is based upon concurrent measurements of high concentrations of ozone on both sides of the C a n a d a - U S . border. The formation of ozone is favored by the same atmospheric conditions as that of sulfate. By 14 August 1976 (Figure 2), high concentrations of aerosol sulfate were found in Nova Scotia. The maximum value was 20 pg/m3, and comprised about 50% of the particulate matter captured by the sampler. By 16 August (Figure 3), however, concentrations were low throughout eastern Canada. An examination of the concurrent surface weather map indicates that the high concentrations of sulfates were located in the warm air south of a frontal system, and appeared to move along with the system. In the warm air, one often encounters a sluggish southwesterly flow, poor atmospheric dispersion and ample sunlight, conditions favorable to the formation and accumulation of pollutants such as sulfates and ozone. It is important to note that, despite the fact that no corrections were made
for local sources or for sea salt, the patterns in Figures 1 to 3 were regional in scale and well organized.
Canada’s sampling network In the early 197O’s, the World Meteorological Organization ( W M O ) initiated a network of 10 “baseline” stations and 100 “regional” pollution monitoring stations around the world (ES&T, August 1978 p 884). A “baseline” station as remote as possible from civilization is operated by Environment Canada at Sable Island, Nova Scotia, while a “regional” station (closer to populated areas but uninfluenced by local sources) is located in Shelburne, Nova Scotia. Among other measurements, monthly composite samples of precipitation are collected by automatic gauges, which are open only during precipitation. The samples are then sent to the Canada Center for Inland Waters in Burlington, Ontario, for analysis of pH, conductivity and standard cations and anions such as ammonium, sulfate and nitrate. In eastern Canada, Environment Canada has expanded on the W M O network; since May 1977, an additional network called C A N S A P (Canadian Network for Sampling Precipitation) has been established. In addition to Sable Island and Shelburne, other stations in the Atlantic provinces are a t Truro, Nova Scotia; Charlo and Saint John, New Brunswick; and Gander, Stephenville and Goose Bay, Newfoundland (Figure 4). There are few indications of temporal and spatial patterns as yet. Measurements of pH in the monthly samples of precipitation, taken since April 1975, at Truro and Gander (both rural locations) had pH values in the range of 4.0 to 4.5, much below the value of 5.6 for “clean” precipitation. The mean pH at Truro was not significantly higher than that at Gander, indicating that there is no decrease in acidity as one travels downwind from the populated areas of eastern North America. Nor was the mean pH a t Truro significantly different from that at Saint John, despite the fact that the former location is rural and the latter is in a heavily industrialized city. These findings would indicate that the patterns of pH in precipitation are primarily regional and not local in character. Other data indicate that acid precipitation is primarily a phenomenon confined to the eastern half of North America. Since April 1975, the concentration of sulfate in precipitation at Shelburne has ranged from 0-9 mg/L. Similar values were found throughout the reVolume 13, Number 4, April 1979
407
FIGURE 1
High aerosol sulfate concentrations in the Great Lakes area,.
o.l
.
0.7
4.6 0
SO, = (fig/m') 12 Aug 76
FIGURE 2
.. are
Nova Scotia, but..
. 2.4 15
SO, = (rg/m') 14 Aug 76
gion, and were also found by the O E C D study in Europe. While there is great variability in the record, there seems to be, even in the scant three years of monitoring, maxima in early winter and late spring/early summer and a minimum in late autumn/early winter. Similar results were found at Sable Island, the other station in the region with a record of three years. The early winter maxima may be due to an increase in emissions at the beginning of the heating season, but it is suspected that the late springlearly summer maximum is primarily meteorological in nature, since it occurs between the major heating and air conditioning seasons. Almost certainly, the mean direction of the atmospheric flow in the lowest 2 km (the layer which the O E C D study showed to be that in which transport takes place) is a very important factor, as we will see in examining the results of aerosol sulfate sampling later in this article. The concentration of nitrate in precipitation at both Sable Island and Shelburne showed the same late spring/early summer maximum and late autumn/early winter minimum as that of sulfate. Because NO2 emissions do not have the seasonal variation of SO2 emission (only 25% of NO2 emissions come from space heating and power generation; 63% is from transportation, which does not vary seasonall)), the seasonal pattern in nitrate lends height to the argument that the early summer peaks of sulfate and nitrate concentration in precipitation may be caused primarily by meteorological factors. Nevertheless. one should be cautioned that the available record is only three years long and may not be representative of the long-term pattern.
Aerosol sulfate Every third day since April 1978, Environment Canada has been collecting 24-h samples of aerosol sulfate and total suspended particulate matter by a high-volume sampler at the Head of St. Margaret's Bay, a rural location about 25 km west of Halifax, Nova Scotia. I n the 60 samples that have been analyzed thus far, the concentration of suspended particulate matter varied from 3-63 pg/m3, with a mean value of 15 p g / n ~ 3Concentrations . of aerosol sulfate varied from nondetectable ( < 2 p g / m 3 ) to 15 pg/m3, with a mean value of 4 pug/m3. On the average, aerosol sulfate comprised 26% of the total suspended particulate matter. For comparison, the O E C D study showed mean annual concentration of sulfate in Europe in 1974 ranging from I - 12 4 m 3 .
FIGURE4
etwork for sampling precipitation
Sable Island ead of St. Margaret's Bay
The sulfate data were simply stratified into two broad categories: days upon which the air arriving at the sampler had passed during the previous 1-2 days over populated areas in the eastern U.S. and central Canada days upon which the air had passed over relatively unpopulated areas. These two categories were each divided into two subclasses: days during which measureable precipitation had been recorded at the climatological station at St. Margaret's Bay and those on which it had not. The results are sholfn in Table I . The concentration of aerosol sulfate on the 22 days with precipitation was not significantly less than that on the 38 days without precipitation. This apparent lack of washout of aerosol sulfate must be viewed with caution, however, since most of the precipitation was in the form of light, local showers. There was, on the other hand, a significant increase in aerosol sulfate when the air had come from populated regions than when it had come from unpopulated regions. In this case, the mean concentration was 5 pg/m3, as compared to only 2 pg/m3 when the air had come from unpopulated re-
gions. These findings are consistent with that found in the analysis of precipitation chemistry at the C A N S A P stations: the direction of atmospheric flow is, not unexpectedly, a significant factor in the long-range transport of atmospheric pollutants to a given location.
Studies of possible effects The deposition of sulfate and nitrate was calculated for each month at each C A N S A P station from the product of their respective concentrations, and the accumulated precipitation as measured by a standard rain gauge. With the exception of Saint John, New Brunswick, where there are strong local industrial sources, the average deposition of sulfate during the period May 1977-March 1978 was fairly uniform over the provinces of Nova Scotia, New Brunswick and Prince Edward Island and the western part of Newfoundland, varying from 2.2-3.2 kg/ha/month. Labrador and eastern Newfoundland experienced a slightly lower deposition of about 1.8 kg/ ha/month. For comparison, the deposition at Maniwaki, Quebec (in central Canada), was 2.0 kg/ha/ month. Although the concentration of sulfate i n precipitation during this period was somewhat lower in Atlantic Volume 13, Number 4, April 1979
409
TABLE 1
Mean concentration of aerosol sulfate at the head of St. Margaret’s Baya Preclpitation day
2.3 pg/m3 Air originating from nonpopulated region (10 cases) 4.8 pglm3 Air originating from populated region (12 cases) 3.6 pg/m3 Average (22 cases) a
2.5 pg/m3 (23 cases) 5.9 pg/m3 (15 cases) 3.8 pglm3 (38 cases)
Average
2.4 pg/m3 (33 cases) 5.4 pg/m3 (27 cases) 3.8 pg/m3 (60 cases)
From 14 A p r i l 4 October 1978.
Canada than it was in central Canada, the greater accumulation of precipitation caused more deposition of sulfate. Average values in Europe in 1974, as reported by the OECD, ranged from 1 to 5 kg/ha/month. The deposition of nitrate was more variable over the region during the period, ranging from 0.2 to 1.5 kg/ ha/month. The reason for this variability is not known at this time. It is not sufficient to merely document the occurrence of long-range transport and deposition of atmospheric contaminants. It is also essential to determine whether or not there may be adverse environmental effects from these phenomena, if public support for programs to control emissions (which may be on an international scale) is to be gained. The Scandinavians have long been examining the possible effects of acid precipitation upon receptors, but work is only getting under way in Atlantic Canada. The most obvious effect of acid rain on fresh water is the lowering of the pH. Trout and salmon are particularly sensitive to low values of pH; they will not tolerate a p H of less than 5.5. Reproductive failure of fish has been observed in acid conditions. There is also evidence for interference with ion exchange across the gill membranes. Another effect of the lowering of the pH in fresh water is a decrease in plankton, bottom fauna and in invertebrates, thereby reducing the food supply for fish. Another phenomenon of concern, especially in cold regions, is “pH shock,” in which the rapid melting and runoff of an acidic snow cover can cause a drastic lowering of the p H in bodies of fresh water. The pH in spring runoffs has been found to be as low as 3.0. In Sweden, the average rate of decrease of pH has been 0.3 to 0.4 units per decade. In 197 1, 20% of Swedish rivers had a pH of less than 5.5, but none had a pH of 5.0. C. L. Scofield of 410
Nonprecipitation day
Environmental Science & Technology
the New York State Department of Environmental Conservation reports that many lakes in the Adirondack Mountains have experienced a reduction in p H during the past 20 years, and a reduction in the reproduction of fish. Richard Beamish of the Freshwater Institute of Environment Canada in Winnipeg has studied several remote, unexploited lakes in Ontario, and has found that fish populations in them were disappearing, primarily as a result of the high acid content of the lakes. The loss of fish populations resulted from both a long-term lethal effect and failure of reproduction. H e suggests emissions of SO2 from a smelter 65 km away as a probable cause of the high concentrations of hydrogen and sulfate ions in the lakes he studied. The ability of a body of fresh water to withstand the effects of acid precipitation depends upon both the bedrock and the surface materials in its vicinity. Those in areas of non-calcareous rock and acid soils are relatively poorly buffered. Much of the Atlantic region of Canada is composed of noncalcareous rock and acidic podzols; therefore, most bodies of fresh water in the region are susceptible to acidification by precipitation. A most interesting study has recently been done on the quality of 16 lakes in Halifax County, Nova Scotia, by W. Watt, D. Scott and S. Ray of the federal Fisheries and Marine Service. They compared values of pH and concentrations of substances such as sulfate with similar measurements of the same lakes made by Eville Gorham in 1957. The lakes used for comparison had experienced no known physical alterations. In all 16 lakes, the pH levels had declined in the intervening 21 years, with the greater declines occurring in the higher pH (near neutrality) lakes. After correction for the input of sea salt. the concentrations of sulfate were
generally higher in 1977 than they were in 1955, but statistically the difference was insignificant. However, the concentration of sulfate was significantly correlated with the distance of the lake from the city of Halifax where two thermal generating stations and a petroleum refinery (both significant sources of sulfur to the atmosphere) are located. The closer the lake to Halifax, the higher the sulfate concentration. The authors conclude that, in the case of these particular lakes, local sources rather than long-range transport may be the major cause of acidification. Nevertheless, the study does indicate that deposition of emissions from combustion sources, be they local or distant, could be deleterious to productive waters. Acidic precipitation may also have an adverse effect upon soils and vegetation. The leaching of nutrients in the humus (top) layer of the soil may be accelerated and thereby reduce productivity. It is also felt that the number of microorganisms that assimilate nitrogen from the air decrease with increasing acidity. There has been an estimated loss of forest productivity in Scandinavia of about one percent per year, but it is not known whether this can be linked to acid precipitation or to other causes. Most soils in the Atlantic region are podzols, acidic soils whose productivity is greatly dependent upon the pH, which in turn is adversely affected by acid precipitation.
New efforts During the past two and a half years, the Canadian federal government has greatly increased its activities with respect to examining the longrange transport of air pollution. Following a pioneering report completed in May 1976 by the Ontario Regional Board of the Federal Department of Fisheries and Environment, a national scientific committee, composed of various members from throughout the department, was formed in early 1977 and charged with the responsibility of designing a national study plan. After several drafts, the final version of the study plan was completed in March 1978, approved by the management of the Department, and is awaiting approval by the Treasury Board, who have the final word on the allocation of resources. Some components of the plan, however, are proceeding, using existing resources of the department. The Canadian study is divided into five main thrusts: Inventory of man-made and natural sources of sulfur east of the province of Manitoba in Canada and the
Mississippi River in the US., to be followed by similar inventories of NO,, hydrocarbons and mercury. Studies of atmospheric processes such as dry deposition, oxidation of s u 1f u r dioxide, and precipitation scavenging. Design and testing of models of long-range atmospheric transportation and transformation of pollutants that will estimate present and future transboundary fluxes. Continuation and expansion of field measurement and monitoring to attempt to draw trends in the quality of ambient air and precipitation. Studies of aquatic and terrestrial ecosystems to attempt to assess their capacity to withstand or react to the atmospheric loading of materials owing to long-range transport. Some of these activities will be carried out by the national headquarters of the various services within the department. I n addition to the national scientific committee, regional scientific committees have been established which, in turn, have established contact with scientists in the provincial governments, some of which are carrying on their own investigations. For instance, J . Underwood of the Nova Scotia Department of the Environment is carrying out an extensive program of weekly precipitation monitoring, using aulomatic gauges and bulk samplers. Apart from activities which are already under way, such as the routine monitoring of precipitation quality by the W M O and CANSAP stations, and the monitoring of aerosol sulfate, activities in the Atlantic region that are being initiated by Environment Canada are the sampling of organics such as PCB’s in precipitation at TrurQ, Nova Scotia, and Gander, Newfoundland. Also, an intensive study of a “calibrated watershed” in the Atlantic region will probably be located in Kejimkujik National Park in southwestern Nova Scotia. Here, there will be daily monitoring of precipitation quality and constituents in the ambient air such as SOz, sulfate, nitrate, ammonium and other major ions in particulate matter. Also, detailed baseline studies will be carried out of fresh water quality, bottom sediment quality, flora, fauna and solids. Kejimkujik National Park has certain advantages for this type of study as it is away from local sources of atmospheric components such as industry and the ocean, no development is expected in the future, inventories of soil vegetation already exist, and it is well manned by competent park personnel. It is hoped that university re-
searchers will also carry out work in the watershed.
A final word It is becoming increasingly obvious that there is considerable deposition of materials such as SO, and NO, from the atmosphere to bodies of fresh water, soil and vegetation in the Atlantic region. It is also becoming apparent that some fraction of these materials is being imported from areas outside the region, possibly the heavily populated regions of the eastern US. and central Canada. Work is only beginning in this region to attempt to assess the ecological effects of the material being deposited. I f the studies demonstrate that the long-range transport and subsequent deposition of materials do have a harmful effect upon ecosystems, gone will be the days when it is a simple matter of identifying an emission source such as a single smoke stack, or a group of smoke stacks polluting a single individual or well-defined group of individuals such as a neighborhood. While these cases will, of course, still exist, superimposed upon them will be the case of one region of the continent polluting another. It is not practicable on a large scale to render receiving surfaces such as lakes more resistant to the effects of the materials being deposited from the atmosphere. Effects can be reduced only by reducing the quantities of the materials emitted in the source region. Consequently, this may involve control of emissions, possibly on an international scale. This will be no mean feat, because it will be impossible to identify polluters on an individual basis. Obviously, control will have to be exercised on a priority basis, with the largest sources being regulated first. Much has been said recently about the high cost of controlling emissions of air pollutants beyond the level needed to maintain acceptable concentrations in the air within a few kilometers of the emission source. While tfie estimates of these costs may very well be reliable, they represent only one side of the question. Have estimates been made of the possible costs of not reducing emissions? Should we wait until demonstrable harmful effects occur before taking steps to curb emissions? The answer to the second question is “probably not” if we wish to act on the basis of prudence. While answering the first question will be a formidable task, it must be done before any final decision is made not to reduce emissions. It is relatively easy to present an argument against control on the basis
of cost estimated by reasonably wellgrounded technical considerations. On the other hand, it is much more difficult to present an argument for control based upon environmental effects which are, for the most part, at present only suspected to occur. The problem is compounded by the fact that the costs of control manifest themselves very clearly to the public in the form of increased power bills and higher costs of consumer goods. In contrast, the costs of not controlling emissions may only manifest themselves slowly over years, perhaps in terms of decreased productivity of soil and fresh water. These costs, however, may be higher and longer lived than the cost of control, and may even be irreversible. Finally, one often hastily assumes that control of emissions involves only technology. Man’s activities, especially those associated with a high standard of living, result in “residuals”--the leftover material and energy that manifest themselves as air, water, thermal and noise pollution. Obviously, one way to reduce emissions is to reduce the demand upon the activities which produce them. The required change to a simpler, more conservative life-style is a social challenge which makes the technical challenge seem like child’s play.
Additional reading Preliminar) Report of the Intensive Sutfate Study, August 1976, Atmospheric Environment Service, Environment Canada, Downsview, Ontario M3H 5T4 Lafleur, R. J., Whelpdale, D. M., Spatial Distribution of Sulfates over Eastern Canada During August 1976. Paper 7748-3, 70th Annual Meeting of the Air Pollution Control Association, Toronto, Ontario, 20-24 June 1977. Whelpdale, D. M., Large-Scale Atmospheric Sulfur Studies in Canada. Paper presented at the International Symposium on Sulfur in the Atmosphere, Dubrovnik, Yugoslavia, September 1977. Munn, R. E., Secular Increases in Summer Haziness in the Atlantic Provinces. A i mosphere, Vol. 1 1 , KO.4, pp 156-161, 1973.
Roderick W. Shaw is chief of the Air Pollution Dicision of Encironment Canada in Halifax, Noca Scotia. Dr. Shaw is responsible f o r implementing federal air pollution regulations in Canada’s Atlantic procinces, and f o r incestigating local and regional air pollution problems. Coordinated by L R E Volume 13, Number 4, April 1979
411
