Part 1: Introduction & The Age of Ignorance | Part 2: The Age of Dilution
Part 3: The Age of Exclusion | Part 4: The Montreal Protocol/The Three Rs and More
Part 3: The Age of Exclusion | Part 4: The Montreal Protocol/The Three Rs and More
The Age of Dilution
The need for greater dilution to alleviate adverse emission impacts was first suggested nearly two thousand years ago by the Roman writer Strabo who commented on the need for lead smelters to be equipped with chimneys "so that the gas from the ore may be carried high into the air." Indeed, chimneys became the first pollution control devices. Their introduction to home heating not only revolutionized dwellings and society in Europe, but were soon adopted to industrial use. The proliferation of chimneys in cities, however, did little to alleviate the increasing urban air pollution problems. These problems were nowhere greater than in London. By 1377, the importance of chimney height in pollution dispersal was recognized. London may have had city regulations establishing minimum chimney heights as early as the end of the fourteenth century.
In 1772, B. White wrote in his Preface to a reprinting of John Evelyn's famous 1661 air pollution tract Fumifugium,
"Till more effectual methods can take place, it would be of great service to oblige all those trades, who make use of large fires, to carry their chimnies much higher into the air than they are at present; this expedient would frequently help to convey the smoke away above the buildings, and in a great measure disperse it into distant parts, without its falling on the houses below."
The first serious attempts by governments to control air pollution failed because, although the problem was recognized, there was no known solution except banning the activity, an unlikely choice in the early Industrial Revolution. The birth of the Age of Dilution and its catch phrase "Dilution is the Solution to Pollution" came shortly after the First World War. In part, poison gas warfare had pushed the studies of atmospheric dispersion forward.
By 1932, the British Electrical Industry was recommending that stacks be built 2.5 times taller than the height of the surrounding buildings to insure good dilution of smoke and gases. Although few legislative acts required added dilution as a means of reducing pollution, the practice of higher stack and plume heights was well established with design engineers by the end of the Second World War.
Following the Second World War, pollution was still treated as an inevitable part of industrialization, part of the price to be paid for a better standard of living and greater national and individual wealth. However, to varying degrees, countries, states/provinces and cities now began to take some actions to limit the worst pollution effects. These actions were usually based on the use of pollution standards. The aim of these standards was not to achieve clean air or pure water, but to establish maximum, permitted levels of pollutants in the air or water. The goal of the standard was to reduce the concentration of pollutants locally in an attempt to avoid acute health effects in the population or severe damage to crops, livestock or materials. Most engineers and regulators believed that these standards could be achieved through greater dilution by wind, wave and current.
As a result, the philosophy of dilution often instituted measures such as taller stacks, deeper outfalls, and greater distances to sensitive receptors rather than pollution control devices or process reform. The practice of dilution abatement in the atmosphere reached its peak with the construction of very tall stacks such as the 366 m stack built for a Sudbury, Ontario ore smelter which reduced local sulphur dioxide concentrations by one hundred-fold in the years following its construction but spread those gases across eastern North America.
While such dilution measures dramatically reduced the local concentrations of target pollutants, it was soon apparent that they did not solve all problems and brought other problems to the forefront. Acid precipitation was first identified as a local problem in Manchester, England in the 1850s; however, with the misguided policy of constructing very tall stacks, the precursors to acid rain travelled further downwind. Damage to lakes and forests from acidic precipitation in both Scandinavia and eastern North America has been attributed to emissions of sulphur and nitrogen oxides hundreds to thousands of kilometres upwind.
Another mounting environmental concern was bio-accumulation, the process of reconcentrating previously diluted metals and compounds by living tissue. Bio-accumulation showed that many short-term pollution standards were inadequate and that concentrations less than the standards, and at times less than current measurement techniques, could lead to chronic impacts on human health and the biosphere. Examples included the bio-accumulation of DDT in birds which resulted in a thinning of egg shells and an increase in still-born and deformed chicks.