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

(c) International Conventions and Agreements: Concern over emissions of 
acidifying pollutants has led to several international agreements, including the United 
Nations Economic Commission for Europe (UNECE) Convention on Long-range 
Transboundary Air Pollution (CLRTAP) (Geneva, 1979) and its protocols to reduce 
emissions of sulphur (Helsinki, 1985; Oslo, 1994; Gothenburg, 1999) and NO
x
(Sofia, 
1988; Gothenburg, 1999). Two other protocols have also been agreed upon that aim at 
reducing heavy metals (Aarhus, 1998) and non-methane volatile organic compounds, 
or NMVOCs (Geneva, 1991).
(d) 
International Targets/Recommended Standards: The 1999 Gothenburg 
Protocol to Abate Acidification, Eutrophication and Ground-level Ozone sets 
emission ceiling targets for SO
2
, NO
x
, NMVOCs and ammonia (NH
3
) for UNECE 
countries. European Union Member States are also required to meet National 
Emission Ceiling Directive (NECD) targets for 2010. Some countries have set 
national targets that are stricter than those of the international agreements, but few 
have yet met these national targets. 
(e) Linkages to Other Indicators: In addition to annual air pollutant emissions and 
their percentage changes, emission intensities (expressed as quantities of pollutant 
emitted per unit of gross energy used) should be presented in order to assess 
sustainability. This set of indicators is therefore closely linked to issues such as fuel 
mix, annual energy use per capita and transport fuel consumption, in addition to the 
status of abatement technology and expenditure on air pollution abatement within 
individual countries. 

---

97 
METHODOLOGICAL DESCRIPTION
(a) Underlying Definitions and Concepts: Air pollution stems from gases and 
airborne particles that, in excess, are harmful to human health, artefacts and 
ecosystems. Emissions of air pollutants from anthropogenic activities are often 
directly related to the combustion of fossil fuels for energy. However, non-energy-
related emission sources are also significant for some pollutants — for example, 
NMVOCs. Emissions of greenhouse gases, or GHGs (e.g. carbon dioxide [CO
2
], 
nitrous oxide [N
2
O] and methane [CH
4
]), are excluded from the scope of this indicator 
and are described separately in the GHG emissions indicator. 
Sulphur Dioxide (SO
2
): The primary product from the combustion of sulphur is SO
2
. 
However, other sulphur oxide compounds can also be produced; thus, when reported, 
these compounds are to be jointly referred to as SO
x
(sulphur oxides). 
Nitrogen Oxides (NO
x
): The primary combustion product of nitrogen is nitrogen 
dioxide (NO
2
). However, several other nitrogen compounds are usually emitted at the 
same time, such as nitrogen monoxide (NO), nitrous oxide (N
2
O), etc., and these may 
or may not be distinguishable in available test data. Total NO
x
is to be reported on the 
basis of the molecular weight of NO
2
. 
Volatile Organic Compounds (VOCs): VOCs are defined as any compound of carbon 
(excluding CO, CO
2
, carbonic acid, metallic carbides or carbonates, and ammonium 
carbonate) that participates in atmospheric chemical reactions. In some cases, the term 
non-methane volatile organic compound (NMVOC) is used to indicate that methane is 
exempt from the VOC categorization. 
Carbon Monoxide (CO): CO is formed from the incomplete combustion of fossil 
fuels. In most countries the transport sector is the main source of CO emissions. 
Emissions of NO
x
, VOCs, CO and CH
4
contribute to the formation of ground-level (or 
tropospheric) ozone. These ozone precursors can be aggregated on the basis of their 
ozone-forming potential to assess the combined impact of the different pollutants. The 
relative weighting factors are as follows: NO
x
, 1.22; NMVOCs, 1.0; CO, 0.11; and 
CH
4
, 0.014. This methodology is routinely used by the European Environment 
Agency (EEA) for its reporting of ozone formation, but the use of such factors does 
not yet have broad international acceptance. The factors are assumed to be 
representative for Europe as a whole, but on the local geographical scale, the factors 
may vary (for further information regarding uncertainties in these factors, see De 
Leeuw 2002). 
Particulates: Terms commonly associated with particulate matter are particulate 
matter with a diameter less than 10 
μm (PM10), total suspended particulate (TSP), 
primary particulate and secondary particulate. PM10 in the atmosphere can result 
from direct particulate emissions (primary PM10) or from emissions of gaseous 
particulate precursors that are partly transformed into particles by chemical reactions 
in the atmosphere (secondary PM10). TSP consists of matter emitted from sources in 
solid, liquid and vapour forms, but existing in the ambient air as particulate solids or 
liquids. 
Secondary PM10 precursors include SO
2
, NO
x
, NH
3
and VOCs. Reliable information 
on the relative contribution of VOCs to particulate formation is not available. For 

---

98 
estimations of quantities of secondary particulates, aerosol formation factors could be 
used to assess the aggregated particulate formation potential arising from emissions of 
the different secondary pollutants (see De Leeuw 2002). The factors are as follows: 
SO
2
, 0.54; NO
x
, 0.88; and NH
3
, 0.64. It should be noted that, as for the tropospheric 
ozone formation factors, these factors are only a best approximation of the relative 
contribution of the different pollutants and significant local variations may actually 
occur in both urban and rural areas. 
Since the objective of this set of indicators is to describe the impact of human 
activities on the environment, emissions from natural sources (such as forest fires and 
volcanic eruptions) should be excluded from the indicator. 
The indicator should therefore present annual air pollutant emissions and their 
percentage changes. Emission intensity expressed as quantities of pollutant emitted 
per unit of gross energy use could be used to assess sustainability. It would also be 
useful if policy-relevant information on emission targets were included in the 
indicator (if such targets exist for a given country). This would allow an assessment of 
the ‘distance to target’ for a country, and hence whether existing pollution abatement 
measures are sufficient to meet existing national or international targets.