GENERAL FRAMEWORK AND SYSTEMS

ABSTRACT

In the tradition of the study materials flows through society, the Substance Flow Analysis (SFA) method is presented. SFA aims at providing the relevant information for a country's overall management strategy regarding single substances or coherent groups substances. This article is dedicated to the presentation of a three-step general framework for studies, and elaborates on its first step, the systems definition. Attention is given to the definition of the external and internal system boundaries, the categorization of the elements, aspects of materials choice, time, and space, and how these depend on the aim the conducted study. Moreover, a broader discussion is on the need for standardization of materials flow studies in general.

2.1 Introduction

The economic production, use and disposal of materials cause major environmental problems. In circles of both economists and environmentalists, resource depletion is identified as a major problem. Still more pressing are the pollution problems arising from the emission of hazardous substances to the environment. One can regard pollution problems and their origins from many different viewpoints, and come up with widely varying types of solution. The first step, however, must be an analysis of the problem in physical terms: the flows of the substances themselves. A basic concept in this field that has been developed to enlighten the economy-environment relationship is that of industrial metabolism, as defined by Ayres (1989). This concept argues the analogy between the economy and environment on a material level: the economy's "metabolism" in terms of materials mobilization, use and excretion to create is compared to the use of materials in the biosphere to create Whereas the biosphere has had billions of years to evolve and attune its processes to such a state that waste generated in one process is convened into a resource for another, the economy is still in its early stages of wastefulness. In order to speed up evolution', society must look to the biosphere for directions. An important research instrument in this field is the materials balance, a tool for describing the materials regime of the economy, again in analogy to the long-standing practice of investigating ecological materials cycles. The description of the economy thus is limited to a description of the physical economy. Substance Flow Analysis, the subject of this article, is based on the materials

balance

Materials balance studies have been conducted from several angles. River basin studies

& Anderberg, 1992) have shown that the origins of water pollution have been shifting from industrial pollution to consumer emissions over the past few decades. studies (Ayres et 1989) have raised suspicions of hidden pollution problems by signalling 'missing' amounts of materials. Another fruitful application of the materials balance approach has been to investigate the flows and stocks of individual substances or substance groups in the economy of a given region (Brunner & Baccini, 1992; Bergbäck et 1992). This application also allows the key flows or stocks for regulation in that region to be identified, and the of certain

' This contains an article in the Environmental Science and Pollution

Research: VOET, E. VAN DER; R. L. VAN R. R. P. MULDER: Studying flows through the economy and environment of a region - Part I: systems definition. ESPR vol.2 pp 89-96.

abatement measures to be assessed. The ensuing picture of the economic life cycle of a substance may be regarded as an important analytic tool for developing a regional pollution policy.

Most studies on the materials flows in a region can be described as inventories: collecting as many data as possible on flows and stocks, and organizing these in an overview that can be used to draw conclusions relevant for a materials management policy. Various attempts have been made to model flows, as a means of predicting the changes in materials flows resulting given societal developments or policy measures. Most of these models are concerned with relatively small parts or suhchains (Gilbert & 1992), or focus on emissions and the environment et 1990). Economic Input-Output analysis, as developed by Leontief (1966), is recognized as a potentially useful technique for incorporating the sum of all economic or societal flows in one model. Several theoretical as well as practical exercises have been undertaken in this direction (for example et 1972; Victor (1972) describes some more of these approaches; more recent examples can be found in Duchin (1994), Idenburg (1993) and Konijn There is as yet no standardized methodology for conducting such studies. It could be argued that there is no need for this because the basic idea is simple: a description of the (yearly) exchange of materials between the lithosphère, biosphere and or, in other words, between the immobile geological stocks, the environment and the economy. However, studies carried out at different institutes are difficult to compare because the choice of elements within the system and the categorization of the various inputs and outputs are made in different ways, and the system boundaries vary from case to case.

The subject of this article is the Substance Flow Analysis (SFA) method, a method for the description and modelling of the flows and stocks of one substance or a group of substances in the economy and environment of a region. A discussion concerning harmonization of efforts in this field is started, especially in Section 2.2. This section contains a description of a general framework for materials flow studies and some basic choices that must be made at the start of each study. In Section 2.3, the position of SFA in this field is treated, together with the SFA system definition. Section 2.4 is dedicated to discussion and conclusions. In Chapter 3, the modelling of substance flows is discussed. Different modelling techniques are described and clarified with the help of an example system.

2.2 General

In general terms, materials flow studies comprise the following three-step procedure: - definition of the system

- quantification of the overview of stocks and flows - interpretation of the results.

All three steps involve a variety of choices and specifications, each of which depends on the specific goal of the study to be conducted, as will be argued below.

System definition

The first step in any materials flow study is to define the system. The system must be determined with regard to space, function, time and materials. If necessary, the system can be divided into subsystems. The various categories of processes, stocks and flows belonging to the system must be specified. Finally, this results in a flow chart: the specification of the network nodes. In this section, some general aspects of the system definition will be treated in relation to the goal of the study.

"regional" or a "functional" approach (Van der Voet & Heijungs, 1994).

In the regional approach, the point of departure is the area itself as a geographically bounded system and what actually takes place there. The location determines which processes (extrac- tion/production/consumption/waste processing) take place within the system, and to what extent. The regional approach would seem appropriate for analyzing the pollution problems of a specific area. In the approach, the point of departure is the fulfilment of functions for the population of a given region. The first step is to establish consumption within the region; this serves as the basis for selecting the processes to be in the system. Any relevant steps taking place outside the region must then also be included. Processes taking place within the region for the benefit of other regions (e.g. production for export) are not part of the system. As a result, a picture is not obtained of the regional environmental situation, but of the extent of the substance's life cycle and its losses to the the benefit of the region, regardless of its location. Both approaches are relevant and both have been applied in practice. The functional approach is followed, although implicitly, in the introduction of the "ecological rucksack"

concept, for example 1993).

A second general aspect concerns time. Studies on flows automatically imply a time dimension: materials flows are expressed in mass units per time unit. Generally, and also in the SFA studies conducted to date, a one-year period is chosen. This seems to be a suitable choice from the point of view of both data availability and policy formulation. In some cases a shorter time period would be more advisable, for example when the variations in time within the year are also relevant, which is well-conceivable, especially for flows. In other cases a longer period would be more appropriate, for example when a slow stock-building process is being monitored.

A third choice involves the materials to be studied. Some studies follow flows and stocks of materials at a totalized level, as proposed by Kneese et al. (1972) and later by Simonis (1994) and Schmidt-Bleek et (1993). In others, only one substance is studied at a time (for example, Anderberg et 1989). Sometimes, the object is a compound material & Van Dalen, 1993), (incorporated) energy (Odum, 1992), or coherent groups of materials et 1994). This choice, too, depends on the specific questions to be answered: totalized materials studies may provide relevant information on the "materials intensity" of a society, while one- substance studies, on the other hand, are relevant for establishing the contribution of a society to specific pollution problems.

In Section 2.3, these basic choices will be specified for the SFA method and the SFA system definition will be treated in more detail.

Quantification of the overview of flows and stocks

The quantification of the network is the next step. This involves identifying and collecting the relevant data on the one hand, and modelling on the other. Three possible ways of modelling the system are briefly discussed in this article, all three types having their own data requirements, as

as their own potential for policy support:

- bookkeeping: organizing the collected data on the identified flows and stocks into a consistent overview;

- static modelling: defining the system's flows and stocks as variables dependent on others, resulting in a set of equations to be solved for one specific year or for the "steady state" equilibrium situation;

- dynamic modelling: including in the modelling also the changes in the system's stocks and flows over time.

A bookkeeping system, although it can hardly be classified as a model, provides very relevant information for environmental policy. The input for such a system consists of data regarding the of the system's flows and stocks of goods and materials, that can be obtained from trade and production statistics, and if necessary also data regarding the content of specific substances in those goods and materials. Emissions and environmental flux or concentration monitoring can be used for the environmental flows. A combination of those data together with application of the mass balancing principle then must lead to the desired overview of flows and stocks. The overview thus obtained may serve various

- identifying problem flows, economic leaks or inefficiencies in materials use in a given year, thereby indicating which flows to regulate;

- identifying potential future problems by signalling large economic stocks or increases of stock that will enter the waste stage sooner or later;

- monitoring changes in flows and stocks over the years, thereby making it possible to verify predictions, obtain an impression of the effects of certain policies or identify growing flows or stocks as potential problem flows in the future.

The bookkeeping overview may also serve as an identification system for missing or inaccurate data.

For static modelling, the most important data are variables describing the relations between the flows and stocks of the system. Emission factors, but also distribution factors over the various outputs for the economic processes and partition coefficients for the environmental compartments can be used as such variables. A limited amount of "bookkeeping" data is required as well for a solution of the set of equations. Static modelling can be used for various purposes. Two are mentioned here, both aimed at specifying the economy-environment relationship in a quantitative way:

- analyzing the causes of environmental problems by tracing back identified problem flows (or stocks) to their economic origins;

- predicting the effectiveness of pollution abatement measures, or the (side) effects on environ- mental problems of other measures influencing economic materials flows.

For a dynamic model, additional information is needed with regard to the time dimension of the variables: the life span of applications in the economy, the half-life time of compounds, the retainment time in environmental compartments and suchlike.

With a dynamic model, calculations can be made not only on the "intrinsic" effectiveness of packages of measures, but also on their anticipated effects in a specific year in the future, and on the time it takes for such measures to become effective. A dynamic model is therefore the most suitable for scenario analysis, provided that the required data are available or can be estimated with adequate accuracy. On the other hand, the data and modelling requirements are by far the most extensive.

Again, a choice for any one of these three types of modelling depends on the aim of the study to be conducted. In Chapter 3, modelling is discussed in more detail, together with the implemen- tation in the computer program SFINX which has been developed as a tool for substance flow studies.

Interpretation of the results

Three types of are distinguished here: Evaluation of the robustness of the overview quantification 2. Translating the overview into policy relevant terms

- linking the overview to an evaluation system

3. Linking the overview to policy instruments.

Ad 1. Uncertainties in data may lead to uncertainties in the quantified overview. It cannot always be estimated beforehand how certain inaccuracies may influence the results. A sensitivity analysis can be conducted (case-by-case) to ascertain whether known or suspected inaccuracies undermine the results. On the other hand, accuracy is not always required to the same extent. A status quo report must give a quite accurate picture of the situation, be it on a generic level. A prediction of a future situation must be accurate enough to provide a basis for policy decisions; policy makers therefore must be able to evaluate it in terms of policy goals with regard to emissions, environ- mental quality, or set targets for the economic flows. For a comparison between alternative measure packages a statement regarding which package is the better one often suffices, and therefore no evaluation of the flows and stocks in an absolute sense is required. Sometimes the uncertainties in data may leave doubts as to whether absolute statements based on the overview would be valid, but will allow relative statements without difficulties.

Ad 2. The quantified overview of stocks and flows must serve as a basis for policy decisions regarding the management of substances and/or materials. Yet the overview is not always easy to evaluate in terms of policy objectives, on the one hand because it is too complicated to distill the right information, and on the other hand because additional information might be needed.

The emissions and environmental flows can be evaluated with the help of policy target, standards or objectives, in order to establish whether these flows are problematical or will be in the future. In such a case, a translation step is often required from flows to environmental

If a group of substances is being studied, an additional step is needed to translate the flows of the different substances into comparable terms. This may be simply kg matter, as is the case with the calculations of the mass intensity of economies by Simonis (1994). In other cases, when the environmental risks are relevant, a conversion must be made to contributions to specific environmental problems ("acidifying potential", "global warming potential", etc., similar to the procedure used in the impact assessment step of the product Life Cycle Assessment (Guinée et Another, frequently discussed issue is the linking of the overview of flows and stocks to some sort of economic model. This may take a wide variety of forms, from introducing economic parame- ters for calculating the pathways of the flows and stocks, through linking the flows model to an economic evaluation model, to adding materials flow overviews to the System of National Accounts. This issue is both highly relevant and extremely complicated, as is reflected in the fact that after decades of discussion little progress has been made on implementing operational systems.

A powerful help for the evaluation of the overview is the definition of indicators & Verbruggen (eds.), 1991). Indicators can be selected from the overview, by singling out a specific flow or stock as the relevant one to follow, or they can be calculated directly from the overview. Indicators may be defined for environmental flows and/or stocks, as an addition to the numerous environmental quality indicators already existing. In this field, an indicator that can be calculated from the overview has for example been developed for the problem of eutrophication

& Opschoor, 1992). Rather less numerous are indicators for the economic substance flows, which could be called indicators for integrated chain management and have bearing on the (possible, future) losses from the economy to the environment, or in other words the leaks out of the economic cycle. In this field, the overview of economic stocks and flows could contribute in an manner. To mention a few possibilities: the already mentioned economy's materials intensity, the economic throughput, the efficiency of groups of processes, the secondary vs. the primary materials use, the economic accumulation all can be calculated from the overview and could serve as indicators for the metabolism of the society. A third possibility is the identification

of indicators for the system as a whole. We could think here for example of comparing the magnitude of the economic cycle of a certain substance with that of the natural cycle, to have some sort of indication of the potential risk et 1993). This goes in the direction of the study of cycles and their transformation by man's activity into

cycles (Schlesinger, 1991; Walker, 1991).

Ad 3. In some cases, the overview is prepared with the aim of linking it to a specific policy