In the third step of the process, a quantitative inventory is developed. Activity volume data ("activity rates") and process-specific information and data are gathered to be used to calculate estimated mercury releases from the identified mercury release sources in the country (or region) in question. In this section, the involved data types are first presented, then general advice on data gathering is given in section 4.4.5. It should be emphasized that data gathering is not limited to this step of the procedure, but may be necessary throughout the process of developing the mercury inventory.
As a preliminary step, it may be considered to create an interim inventory to support the prioritization of the further work and initiate communication with inventory participants/reviewers. An interim inventory may present the identified source sub-categories along with indication of their relative importance. A preliminary impression of the relative importance - magnitude of mercury releases - of the identified source sub-categories can be formed by gathering and applying activity volume data (see below) and/or other relevant information such as the approximate number and size of facilities in a particular industry, approximate number of people engaged in a particular activity, such as gold mining, or similar. An interim report can be developed with outline as described in section 4.5.3.
The basic aim of the Toolkit is to enable an estimation of the average annual release to each pathway or vector (air, water, land, products, general waste, sector-specific waste treatment) for each release process identified. The estimate can be calculated using the following basic equation:
EQUATION 1:
Estimated mercury
release to pathway X
=
activity rate * input factor * output distribution factor for pathway X
In other words, the annual estimated mercury releases for each pathway is calculated by:
Multiplying the amount of feed material processed or product produced per unit of time (e.g. tons or pieces per year) – referred to as the activity rate - with
An “input factor”. For sub-categories with only one life-cycle phase (such as coal combustion) the input factor is the mercury content (e.g,. in grams of Hg) per unit of feed material processed. For sub-categories with more than one life cycle phase (such as battery production), the input factor is defined for each phase. For example, the input factor for the production phase is amount of mercury released per metric ton of batteries produced or product produced (e.g., metric ton or piece) – referred to as the input factor –
and the fraction or part (unit-less) of the mercury input that is released through the particular pathway (air, water, land, product, general waste, or sector specific waste treatment) - referred to as the output distribution factors.
However, it is important to note that the input factors for many sub-categories are more complicated than defined above. For sub-categories with only one dominant life-cycle phase (such as coal combustion or waste incineration) the input factor is the mercury content (e.g. in grams of mercury) per unit of feed material (e.g. coal, waste, etc.) processed. For sub-categories with more than one life-cycle phase (such as batteries or thermometers containing mercury) the input factors are more complicated and must be defined for each phase.
It is also important to make sure that the units for activity rate, input factors and releases are appropriately used in the calculations. If the units are not consistent (and do not result in correct mathematical results), conversion factors must be used to convert the units correctly, to assure that units follow proper mathematical calculations. The mercury releases per year should be calculated and presented in kg (or metric tons) of mercury per year for each relevant pathway (such as kg of mercury emitted to air per year). Note that, in the source description sections in chapter 5, input factors are presented in the most relevant (metric) units to enhance readability. Make sure that these units are converted to the right level of magnitude to result in releases in Kg in the reporting.
In this Toolkit, it is suggested to assess and present all mercury releases individually to promote transparency and a uniform procedure. On the summary level of the inventory report, all the releases to a specific pathway are summed up for each source sub-category (and main category). This is done for each of the pathways relevant for the life-cycle of the sub-category in question. See the example given below, and section 4.5 on presentation of the inventory.
For some sub-categories, the actual sources may be a limited number of well-defined point sources (with a specific geographical position), often with individual plant-specific characteristics. In such cases, the point source approach is applied. The estimate of total national (or regional) releases from this sub-category is calculated as the sum of the mercury releases (calculated with equation (1)) for each individual point source present nationally (or regionally).
Sub-categories where a point source approach might be most optimal include, among others, large coal fired power plants, municipal waste incinerators, chlor-alkali production and cement production.
For other mercury sources, a point source approach might not be relevant, might be difficult to implement, or just not optimal. Instead, an overview approach can be applied. This is the case for sources, where releases are not confined to a specific geographical position (sometimes also called "area sources"), sources where the available data are inadequate to perform an inventory with the point source approach, or sources where the point sources are operated under very similar conditions. In such cases the total national (or regional) releases from the sub-category may be calculated using national (or regional) activity rate numbers combined with general mercury input factors and output distribution factors, or by extrapolating releases from a few well documented point sources to the national or regional scale (using point source and national activity rates to scale up the release estimates).
Sub-categories where an overview approach is recommended include, among others, residential coal combustion, disposal of mercury thermometers, cremation and landfills.
In order to assist users of the Toolkit to estimate the releases from individual sub-categories, the main, recommended approach for each sub-category is indicated in the sub-category overview tables in section 4.3 and chapter 5. The point source approach is abbreviated "PS" and the overview approach is abbreviated "OW" in these tables.
Calculation of individual releases throughout the life-cycle
Within a specific sub-category, the releases from the relevant phases in the life-cycle are calculated individually, but described in the same section of the inventory report.
For each source sub-category described in chapter 5, an indication is given of the main release potentials for each phase throughout its life-cycle (production - use - disposal) and to which environmental media the releases are likely to happen. The information is given both in the text and in a table, as shown below.
Table 4 14 Example of an overview table indicating main releases and receiving media in the life-cycle of a product or service (here for batteries with mercury)
Phase of life cycle
Air
Water
Land
Products
General waste
Sector specific treatment/
disposal
Production
X
x
x
X
x
Use
Disposal
X
X
X
X*1
Notes: *1: Separately collected batteries containing mercury (or categorized under sorting as
such) may be disposed of in specially secured landfills;
X - Release pathway expected to be predominant for the sub-category;
x - Additional release pathways to be considered, depending on specific source and national situation.
It should be noted that within a specific sub-category, a point source approach may be best for estimating releases from the production phase, while the overview approach may be most suitable for the use and disposal phases. This is, for example, the case for mercury thermometers, where a country may only have one or a few thermometer factories, but where mercury thermometers (including imported thermometers) are used for a variety of purposes spread on the whole geographical area of the country, and are broken or disposed of locally.
Examples of calculation of mercury releases
Section 4.4.7 displays three examples of calculations of inputs and outputs for selected source categories. In the examples, the following table is used to sum up the results from the calculations. The table enables the presentation - in summary - of all the data included in the calculations, and the results of the calculations.
Table 4 15 Example of a possible table presenting, in summary, the estimated mercury releases for a specific sub-category
Notes: *1 [(Cross) reference to where input factors where taken from or how they were developed];
*2 Sub-calculation for use in the reporting with formula "Input = input factor * activity rate" for each phase;
*3 [(Cross) reference to where input factors where taken from];
*4 Calculated with equation (1) for each of the pathways within each phase, for example: Mercury
release to air from production = activity rate production * input factor production * output
distribution factor to air for production.
