Contaminant release in IEHIAS

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The text on this page is taken from an equivalent page of the IEHIAS-project.

The point at which contaminants are released into the environment is crucial for risk management, because it represents the last point at which pollution can be directly controlled; once released, the only options available are to attempt to mitigate the impacts in some way. By the same token, impact assessment relies on knowledge about contaminant releases in order to estimate the resulting patterns and levels of environmental pollution, the potential for human exposure and the degree of risk that these represent.

Six main characteristics of the releases are important in this context:

  • their source - i.e. the activity or process from which they originate
  • their location - where they occur and at which height
  • the release mechanism - the processes by which release occurs
  • the release pathway - into which medium the contaminant is being released
  • their composition - the types of contaminants involved and, in some cases, the temperature of the release
  • the release rate - the mass or volume released per unit time and area

A range of information sources exist, providing data on these characteristics of releases, including a number of release (or emission) inventories which have been set up for regulation and compliance purposes. Direct monitoring of releases is nevertheless rather limited, and confined mainly to large combustion facilities (e.g. power stations). For the large majority of sources, releases have to be estimated more indirectly, using some form of emission modelling. These typically require a range of data inputs, including information on the source activity and intensity (e.g. how much of the chemical is being used and for what purpose), and some form of emission factor, detailing the average rate of release per unit of usage.

Release pathways and processes

Contaminant release represents the point at which a pollutant escapes from its source into the open environment. Release can occur from both natural and anthropogenic sources, and in the latter case either deliberately or accidentally. Release can also occur into different environmental media (e.g. the atmosphere, surface or subsurface water, soil, biota), and via a range of different mechanisms. How releases occur, and into which medium, depends to a large extent on the sources concerned, as the figure to the right indicates.

Release mechanisms 0.jpg

Release inventories

A wide range of release inventories have been developed, for different sources, contaminants and study areas. In the EU, the most definitive source is the European Pollutant Release and Transfer Register, which provides information on releases of 91 pollutants into the air, water and soil from ca. 24,000 industrial facilities covering 65 economic sectors. Many countries and municipalities also maintain national inventories, offering data and mapping capability at a higher spatial resolution. In addition, specialist inventories have been developed, both regionally and globally, targetted at specific sources (e.g. road transport, airports), release pathways (e.g. air, water) or pollutants (e.g. greenhouse gases, mercury). Links to many national and international inventories are provided by the portal, and the OECD Centre for PRTR Data, as well as by the Opasnet website (see link below).

Inventory methodology

The information contained within these inventories is derived in a number of different ways. A broad distinction can be made between 'bottom-up' and 'top-down' approaches. In the former, inventories are built up by aggregating detailed information from individual sources (e.g. industrial facilities, road links) or small areas (e.g. residential zones); in the latter, broader (often national) data are disaggregated to a more local level. While the former methods can sometimes make use of direct measurements of releases (e.g. at major point sources), the majority of the data are derived from modelling. Bottom-up inventories generally involve the use of the standard emission formula (see link to Modelling contaminant releases in panel to left), in which a measure of source activity is multiplied by an emission factor for each locality (e.g. each grid cell or administrative area). In top-down inventories, similar formulae are typically applied at an aggregated (e.g. national) level, and then the estimated emissions total reapportioned to a more local scale using data on relevant proxies, such as population density, GDP, employment or land cover.

Uncertainties in emission estimates

The data provided by emissions inventories are inevitably uncertain. Major sources of uncertainty include:

  • biases in the sample of sites for which direct measurements are available (often the larger and better regulated facilities);
  • uncertainties in the emission factors;
  • uncertainties in the statistical or other data used to represent source activity;
  • poor characterisation of the emission control technologies and their actual efficiency;
  • errors in model formulation;
  • inadequate recognition of the effect of local factors (e.g. facility management and maintenance) on emission rates.

The levels of uncertainty vary, depending on the pollutants and source, and the spatial scale of analysis. Understanding of the uncertainties is probably best for atmospheric emissions. Typical levels of uncertainty at national level in these range from <10% for major criteria pollutants such as sulphur dioxide and oxides of nitrogen to 20-50% for particulates and benzene, and as much as 100% (or even more) for dioxin and benzo(a)pyrene. For releases into other media, for which the inventories tend to be less well-developed, the uncertainties may be greater. Likewise, larger uncertainties may be expected for many estimates at more local scales.

Modelling contaminant releases

Principles of modelling

For many impact assessments, releases of contaminants into the environment have to be modelled, because suitable data do not exist (e.g. where assessments are prognostic and need to estimate future releases under a specified scenario).

The detailed structure of release models varies depending on the source type, contaminant, environmental medium (e.g. air, water or soil) into which release occurs, and details of the application (e.g. spatial scale, time scale). The basic formulation, however, remains the same:

R = S * F

where, R is the release rate (mass or volume/time), S is the level of source activity (/time) and F is the emission factor (mass or volume/unit of activity).

The term F can be further expanded, where appropriate, to take account of emission controls inherent in the source:

F = E * (1-R/100)

where E is the emission rate and R is the emission efficiency (i.e. percentage of emissions removed/withheld by the emission control device).

Data inputs

Information on source activity can be obtained either from the available statistical information, or by modelling (see link to Contaminant sources in panel to left). Established emission factors are also available, for a wide range of source activities and contaminants, derived from direct monitoring of typical sources, from experimental studies or from analysis of input and output data for individual processes. These may allow for recognised emission control technologies; otherwise, estimates of emission effciency need to be derived from independent sources (e.g. test results from technology providers).


A range of release models have been developed for different pollutants and environmental media. LInks to a selection of models and model factsheets are available in the Model section of the Toolkit.

Development of emission scenarios

A scenario is the description of a possible, consistent future state or development of a system. For assessment of mitigation strategies for pollutant releases the development of emission scenarios is necessary. The first step is the generation of a reference scenario, the so-called baseline. For compiling reference scenarios a projection of stock and/or activities needs to be done (taking into account trends and policy interventions and their influence on economic growth, changes in behaviour, and changes in population, etc.). In a next step the activity projection needs to be combined with current legislation and policies in place and in pipeline (e.g. taking into account the 2008 Energy and climate package of the EU, EURO VI implementation, IPPC revision and autonomous technological changes). Usually, the focussed future years are 2020, 2030 and 2050. Emission scenarios are built based on the emission factor approach. That means that activities and emission factors are separately implemented in the data base and emissions are calculated using them. This has the main advantage that the impacts of legislation and policies can be assessed separately for the activity development and the emission factors, because often policies and legislation can have impact to both or only one of them.

Development of emission mitigation scenarios

Emission mitigation scenarios are based on policies and usually developed in relation to a reference scenario. The policies need to be translated to measures or measure bundles, that means a combination of different measures. Measures are distinguished into technical and non- technical measures. Technical measures have an impact on emission factors and non-technical measures affect the activities of the reference scenario. A measure needs to be clearly defined by description of the following issues:

  • Name/title of the measure
  • Pollutants that are reduced by the measure
  • A short description
    • Technical description
    • Affected activity sector
    • Country specific current implementation degree
    • Country specific maximum implementation degree
  • Reduction potential(s)
  • Cost
  • Approach for implementation
  • State of implementation
  • Time horizon for implementation
  • Data sources/References

Emission mitigation scenarios describe a future state in relation to the emission reference scenario. In most cases there exists an end point, the Maximum feasible reduction (MFR) scenario. This scenario describes the maximum mitigation potential, if all available measures are combined in a policy. Policy scenarios typically define cost-efficient target points between the MFR scenario and the baseline scenario.

Emission factors

Emission factors provide estimates of the typical or average rate of emission (per unit of activity) of a specified substance from a specified source or process. 'Activity' in this context can be characterised in different ways, according to the type of source and purpose of the emission factor: e.g. per unit (mass, volume) of material or energy consumed, per unit of output produced, per individual (employee, consumer, animal, livestock unit) or per distance travelled (for transport sources). Together with matching data on source intensity, the factors thus provide a means of estimating contaminant releases.

Emission factors are derived in several different ways, depending to a large degree on the type of source activity and the contaminant concerned. For major controlled or confined sources, such as large combustion plants, direct measurement of releases is possible during routine operation (e.g. by in-stack monitoring); measurements across a sample of these facilities can then be used to estimate emission factors per unit of activity. For smaller or more diffuse sources, such as road vehicles or farming activities, estimates are usually based on observations under experimental conditions, designed to simulate normal activities. Alternatively, factors may be approximated by comparing inputs of the substance of interest contained in the raw materials with that in the usable products; losses can then be estimated by differencing. Where other methods are not possible, estimates may also be made by establishing a relationship between concentrations in the environment and local source activity levels (e.g. between measured concentrations of pollen in the amosphere and the density of source species in the surrounding area).

In all cases, the uncertainties involved in reported emission factors also need to be recognised. These derive primarily from the limited representativeness of the situations from which the data are gathered; inevitably these do not necessarily reflect the range of local conditions and individual behaviours (e.g. in terms of equiment maintenance and use) which may exist. As a consequence, emission estimates based on the use of standard emission factors are highly approximate, and need to be treated with caution.

Databases of emission factors have been extensively developed for emissions into the atmosphere. Effort to develop and use these factors has been motivated, especially, by international initiatives to control climate change and long-range air pollution, but national factors have also been devised for more local uses. Equivalent factors for other media tend to be scarce, and indeed the very concept of emission factors is much less highly evolved in relation to noise, electro-magnetic radiation, water or soil pollution. In these cases, modelling has to rely on other ways of estimating emissions - for example, by reference to industry standards and government regulations on emission levels (such as EU regulations on noise from outdoor equipment and household appliances).

Links to a selection of emission factor databases are given below, and factsheets and data for some key European sources are included in the Data section of the Toolkit. Links to a range of other, ad hoc, data sets are provided in the panel to the left.

See also:

Name Description Link
Co-ordinated European Programme on Particulate Emission Inventories, Projections and Guidance Provides emission factors for particulate matter into the atmosphere, by SNAP category
Greenhouse Gas and Air Pollution Interactions and Synergies Provides emissions factors for greenhouse gases and particulate emissions to the atmosphere
National Atmospheric Emissions Inventory Atmospheric emission factors, as used in the UK national emissions inventory
Factor Information Retrieval Data System Database, and on-line search engine for US-EPA's atmospheric emission factors
Handbook Emission Factors for Road Transport PC-based tool for atmospheric emission factors for regulated and important non-regulated pollutants from road vehicles (covers Germany, Austria, Switzerland, Sweden, Norway)
Noise database Database of permissible levels of noise emissions from non-road vehicles, as specified under Article 16(4) of Directive 2000/14/EC

See also

Integrated Environmental Health Impact Assessment System
IEHIAS is a website developed by two large EU-funded projects Intarese and Heimtsa. The content from the original website was moved to Opasnet.
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