|Industrial Metabolism: Restructuring for Sustainable Development (UNU, 1994, 376 pages)|
|Part 2: Case-studies|
|10. Sulphur and nitrogen emission trends for the United States: An application of the materials flow approach|
Among the substances metabolized by industrial activities, fossil fuels are the most significant, both in quantity and by the variety of chemicals that are mobilized. Industrial consumers take fuels as inputs and exhaust residue products to air, land, and water. Sulphur and nitrogen compounds are major fossil fuel residues that are released primarily into the air and subsequently deposited to land and water bodies.
The elements redistributed by the "industrial metabolism" of fossil fuels are carbon, sulphur, and nitrogen, as well as crustal and trace metals. In fact, these are the main chemicals of which living matter is composed. As such, they are the key nutrients for the plants on earth. However, these substances may be either beneficial or harmful to the receiving ecosystem, depending on their quantity, rate, and chemical form.
In order to assess the possible harm or benefit of fossil fuel residues and the possible remedying actions, it is helpful to construct a complete material flow scheme that describes the end-to-end transfer of these materials as they pass from one long-term geochemical reservoir to another.
In order to construct such a flow model, it is helpful to utilize the ecosystem analogue for the human-induced material flow, which has producers, consumers, and receptors (recyclers) as the key players. A general description and mathematical formulation of the ecological analogue is given elsewhere (Husar, 1986; also see chapter 2 of this volume). The purpose of this chapter is to illustrate the application of the producer, consumer, receptor method to the construction of a sulphur and nitrogen flow scheme for the United States. The essence of the approach is that one follows the path of the fuel or nitrogen from "production," i.e. mining, through the consumers to the environmental receptors. (More details on the methodology can be found in Husar, 1986.) In constructing the materials flow model emphasis was placed on obtaining the relevant data from the measurement records of various US agencies. Also, data were sought for the term trends in order to illuminate the dynamics of the producer-consumer-receptor system.
In the following, the presentation of the fuel production and consumption data sets is accompanied by a discussion of the technological trends for different industrial sectors; the changes in technology were taken mostly from Darmstadter et al. (1987).
Combustion of coal and oil products, along with the smelting of metals, produces the bulk of the anthropogenic sulphur and nitrogen emissions to the atmosphere. The driving force for fuel production is the consumption of energy by different sectors.
From the turn of the century to the 1970s, US energy consumption has been characterized by a steady increase in total consumption and shifts from one fuel to another (fig. 1). From 1850 to about 1880, wood was the primary energy source. By 1900, and during the first quarter of this century, rising energy demand was matched by the increasing use of coal. The depression years of the early 1930s are reflected in a sharp drop in coal consumption, which increased again during the war years in the early to mid 1940s. Coal consumption declined to another minimum in 1960, because the increasing energy demands were supplied by cleaner fuels, natural gas and petroleum. Accelerated oil and gas consumption began in the late 1930s and 1940s, such that by 1950 the energy supplied by oil exceeded that of coal and maintained its rise up to the early 1970s. By 1960, natural gas surpassed coal as an energy source.