Emissions
of nitrogen oxides (NOx)
AP-1
1 Indicator
definition and unit of measurement
The
total annual amount of nitrogen oxides emissions must be derived for all
economic activities, and particularly energy production and transformation,
industry, transportation and domestic and tertiary sectors. The unit of
measurement is Kt NO
x
per year.
2 Placement
in the framework
5EAP:
Chapter
5: The themes and targets of the programme, section 5.2: Acidification and air
quality.
Agenda
21:
Chapter
9: Protection of the atmosphere.
International
conventions and agreements:
UNECE
LRTAP (Geneva, 1979) and protocol on the stabilisation of NO
x
emissions (Sofia, 1988).
Ranking:
Core
ranking:
1
(77%)
Policy
Relevance:
1
(3.5)
Analytical
Soundness:
1
(3.4)
Responsiveness:
6
(2.7)
Most
appropriate related state indicator:
Exceedance
levels of critical loads of pH in water and soil.
3 Significance
Purpose:
Emissions
of nitrogen oxides (NO and NO
2)
arise primarily from the reaction of nitrogen and oxygen during the combustion
of fossil fuels and biomass. The purpose of this indicator is to identify the
activities mostly responsible for the release of nitrogen oxides into the
atmosphere.
Relevance:
Nitrogen
oxides emitted into the atmosphere can be transported over large distances and
can be deposited at the surface often hundreds or thousands of kilometres away
from the site of the source. They are partly responsible for a series of
problems, including acidification and increased concentration of photo-oxidants
in the atmosphere that result in the occurrence of photochemical smog episodes.
Linkages
to other pressure indicators:
Nitrogen
oxides are also referred to as ozone precursor gases and as such play an
important role in the Ozone Depletion processes (see OD-5), since they affect
the rate of creation/destruction of ozone. Emissions of these compounds are
also related to the Urban Environmental Problems policy field (see UP-9), as
they are associated with local effects on the urban population. It must be
emphasised, however, that the present definition of the indicator refers to
inter-boundary air pollution problems related to regional concentration levels
and exceedance of critical loads.
Targets:
The
1988 Sofia Protocol on the stabilisation of NOx emissions, stated that the
nitrogen oxides emissions should not increase from 1980-1985 level until 1995.
At the EU level, a number of directives have been developed for the regulation
of NO
x
emissions from transport (70/220/EEC and 72/306/EEC) and industry, especially
from large combustion plants (84/360/EEC and 88/609/EEC)
targets include a stabilisation of NO
x
emissions at 1990 levels by 1994 and a 30% reduction by the year 2000 as
compared with 1980.
4 Methodological
description and underlying definitions
Underlying
definitions and concepts:
Anthropogenic
emissions outweigh natural contributions, such as lightning and the chemical
transformation of nitrous oxide in the stratosphere. The amount of NO
x
emissions
from all anthropogenic activities is directly related to the combustion of
fossil fuels for energy production.
Measurement
methods:
Local
authorities perform regular inspections in order to determine the conformity of
a number of works and activities with environmental regulations. In this
context, NO
x
emissions are measured (and regulated, where appropriate) for a number of
activities, for example electricity production stations and large industrial
installations. For those activities for which measurements are not directly
available, it is possible to estimate emissions by considering the amount of
fuel consumed (both fossil fuels and biomass) together with emission factors
related to particular combustion processes. In order to determine the
appropriate emission factor for each activity, it is imperative to obtain
relevant statistical data related to the fuel characteristics, and the
machinery specifications taking into account the effects of various control
techniques (e.g. cooling towers, low temperature fuel combustion etc.). It must
be noted that detailed methodologies (such as the CORINAIR programme) already
exist for the estimation of NO
x
emissions from all anthropogenic activities.
Limitations
of the indicator:
The
level of detail required for various combustion processes and particularly data
related to the machinery characteristics might not be readily available for
certain activities. In this case, default emission factors can be used to
obtain estimates of the NO
x
emissions released into the atmosphere.
Alternative
definitions:
Emissions
of nitrogen oxides per unit of area (t NO
x/km2).
