Emissions
of nitrogen oxides (NOx)
OD-5
Ozone
Depletion
Pressure
1 Indicator
definition and unit of measurement
Total
NO
x
emissions from subsonic and supersonic aviation in the higher troposphere or
lower stratosphere. Unit of measurement is tonnes NO
x
per year.
2 Placement
in the framework
5EAP:
Only
relevant for total emissions of NO
x
(see
Chapter
5: The themes and targets of the programme, section 5.2: Acidification and air
quality). See also the indicator “Emissions of NO
x”
in the Climate Change section.
Agenda
21:
Only
relevant for total emissions of NO
x
(see
Chapter 9: Protection of the atmosphere). See also the indicator
“Emissions of NO
x”
in the Climate Change section.
International
conventions and agreements:
The
UNFCCC (New York, 1992) aims at limiting the emissions of greenhouse gases. See
also the indicator “Emissions of NO
x”
in the Climate Change section. So far, agreement has not been reached
concerning the allocation of emissions from international aviation to
individual countries, although countries are required to estimate those
emissions.
Ranking:
Core
ranking:
5
(38%)
Policy
Relevance:
7
(2.5)
Analytical
Soundness:
8
(2.2)
Responsiveness:
4
(2.7)
Most
appropriate related state indicator:
Stratospheric
concentration of NO
x,
overall ozone depletion potential.
3 Significance
Purpose:
The
purpose of the indicator is to measure anthropogenic NO
x
emissions from subsonic or supersonic aviation in the lower stratosphere. Due
to the short life time of NO
x,
NO
x
emitted in the troposphere will not reach the stratosphere. Therefore, the
larger part of anthropogenic NO
x
emissions does not affect the ozone layer. Stratospheric NO
x
emissions have two effects on the ozone layer (see also the indicator
“Emissions of N
2O”
in this section): 1) Less ozone destruction, since NO
x
reacts with chlorine compounds, 2) An increase in ozone destruction, due to the
catalytic destruction of ozone by NO
x.
Relevance:
Since
supersonic aviation is increasing, this indicator will become more important.
Linkages
to other pressure indicators:
Since
NO
x
is a precursor of tropospheric ozone (a greenhouse gas), total NO
x
emissions are accounted for in the indicator for climate change. Furthermore,
since stratospheric ozone affects the greenhouse effect, ozone depletion should
be considered in assessing climate change.
Targets:
No
targets exist for NO
x
emissions from aviation. For targets for total NO
x
emissions, see the indicator “Emissions of NO
x”
in the Climate Change section.
4 Methodological
description and underlying definitions
Underlying
definitions and concepts:
See
indicator “Emissions of N
2O”
in the Climate Change section.
Measurement
methods:
See
indicator “Emissions of N
2O”
in the Climate Change section.
Limitations
of the indicator:
Large
uncertainties are involved in estimating the effects of NO
x
emissions from aviation in the stratosphere.
Alternative
definitions:
None.
