Calculation of emissions

Production emissions

Production emissions of chromium have been estimated for the ferrochrome alloy and steel industries and for leather tanneries. These activities contributed more than 90 per cent of the chromium emissions to water, and almost 100 per cent to the air in the late 1970s, according to estimates by the Swedish Environmental Protection Board.

For lead, the emissions have been calculated for metalworks, the iron and steel industry, glassworks, the rubber industry, and battery manufacturing. These branches were responsible for approximately 95 per cent of the emissions to air and water in the late 1970s.

The method for calculating time series for production emissions has been to use the best available single-year estimate of uncontrolled emissions for the various branches. We then let the emissions follow the development of production and/or use of lead/chromium backward in time. The emissions from a particular branch of industry were distributed between the individual factories according to the number of workers employed, or the production figures at different periods in time (10-year periods, except for the first and last periods, where five years were used). Finally, the total emissions per time period and region were summed up.

Consumption emissions

For consumption emissions, specific factors for various products have been used (see below). Here, the emissions were distributed between regions according to the distribution of population, except in the case of gasoline, where sales statistics were used.

The diffusion of lead or chromium from a certain use was calculated as follows

A x E x T

where A is the share of total lead/chromium consumption for the particular use, E is the assumed emission factor, and T is net consumption, from which the consumption of lead in gasoline and ammunition has been subtracted. The emission factor (see table 1) is defined as the part of the product that is mobilized in the environment within a decade. (Here we have used the factors given by Tarr and Ayres, 1990.) The emissions from gasoline and ammunition have been calculated separately, assuming that 80 per cent and 100 per cent of the lead content, respectively, will reach the environment.

Table 1 Emission factors for calculation of consumption emissions

Source: Tarr and Ayres, 1990; Ayres and Ayres, in this volume.