Energy Indicators for Sustainable Development: Guidelines and Methodologies International Atomic Energy Agency United Nations Department of Economic and Social Affairs International Energy Agency Eurostat European Environment Agency

(b) Measuring Methods: In some cases emissions from, for example, industrial 
plants can be estimated based on actual direct measurements in stacks or by material 
balances. However, in general, pollutant emissions are calculated with the help of an 
emission factor, which is a representative value that attempts to relate the quantity of a 
pollutant released to the atmosphere with an activity associated with the release of that 
pollutant. These factors are usually expressed as the weight of the pollutant divided by 
a unit weight, volume, distance or duration of the activity emitting the pollutant (e.g. 
kilograms of particulate emitted per tonne of coal burned). Such factors facilitate the 
estimation of emissions from various sources of air pollution and ideally are known 
on a facility- or country-specific basis. In most cases, these factors are simply 
averages of all available data of acceptable quality and are generally assumed to be 
representative of long-term averages for all facilities in the source category (i.e. a 
population average). 
Work to standardize sampling and analytical methods for air pollution has been 
completed by the International Organization for Standardization, the World 
Meteorological Organization (WMO), the World Health Organization (WHO), the 
UNECE, the Organisation for Economic Co-operation and Development (OECD) and 
the Co-operative Programme for Monitoring and Evaluation of the Long-Range 
Transmission of Air Pollutants in Europe (EMEP). 
Similarly, in recent years, considerable effort has been made to standardize or 
harmonize the calculation of national emission inventories for air pollutants in order 
to improve the comparability of national estimates. There have been a number of 
initiatives that provide guidance to countries on the creation, compilation and 
reporting of pollutant release inventories. These include the EMEP/Corinair 
Guidebook (EMEP/EEA, 2004), the OECD Pollutant Release and Transfer Register 
(PRTR) programme guidance (OECD, 1996), and the United Nations Institute for 
Training and Research (UNITAR) guidance on pollutant release and transfer registers 
(UNITAR, 1997). The last of these is specifically designed to support and facilitate 
the national PRTR design process within developing and industrializing countries. 

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In the first instance, countries should consult existing information sources to obtain 
specific guidance on, for example, energy sector definitions and the recommended 
emission estimation or measurement methodologies. Regarding the reporting of 
inventories, estimations of data from previous years are typically subject to revision as 
estimation methods become better and countries shift from using default emission 
factors to country-specific factors. 
To assess sustainability, ideally it would be possible to study the trends in emissions 
over long time periods (e.g. 20 or 30 years). However, even within Europe, where air 
pollutant emissions have been reported for a number of years, reported emissions for 
years before 1990 are generally not complete and may also be unreliable due to the 
non-availability of historical activity data, technology-specific emission factors, etc. 
Time series reporting should therefore initially focus on accurate reporting from 1990, 
the baseline reporting year for many international agreements.