ANNEX ATMOSPHERE
INDEX
1
Introduction .............................................................................................................................. 2
2
Definition................................................................................................................................... 2
2.1 Flow connection scheme ..................................................................................................................... 2
2.2 Nitrogen deposition definition ............................................................................................................ 3
2.3 Nitrogen pollutant definition............................................................................................................... 5
3
Inflows and outflows ................................................................................................................. 7
3.1
3.1.1
3.2
3.2.1
Emission sources............................................................................................................................ 7
Suggested Data Sources ............................................................................................................ 8
Nitrogen deposition ....................................................................................................................... 9
Suggested Data Sources ............................................................................................................ 9
4
Uncertainties ........................................................................................................................... 10
5
References............................................................................................................................... 11
6
Document version ................................................................................................................... 13
1
Introduction
Atmosphere is used mainly as a transport medium, as the atmosphere serves to collect, to deposit and to
transport reactive nitrogen under various chemical forms. Even though most of the available nitrogen is
stored here in the form of inert molecular N2, only the fraction present as Nr or being converted to or from
Nr must be quantified. The quantification of conversions between compounds different possible
atmospheric sub-pools (e.g., oxidized or reduces Nr-species) is not required, except for N2 fixation to NOX
due to lightning, which is considered as an input flow. Other input flows are atmospheric import of Nr, as
well as emissions from all other pools in a National Nitrogen Budget (NNB). Also fluxes of N2 from pools to
the atmosphere are regarded as input flow. Output flows are biological and technical N-fixation, export of
Nr by atmospheric transport and Nr-deposition to land-based pools. N fixation is not so important for the
Atmosphere pool, but detailed information and data could be find in the Agriculture pool.
2
Definition
In the following paragraph the main parameter definitions will be provided.
2.1 Flow connection scheme
In figure 1 the N budget scheme for the pool ‘Atmosphere’ is reported.
Figure 1 – N budget scheme for the Atmosphere pool.
The input flows are the N fluxes (as tons of N emitted) from all the other pool (‘Energy&Industry’, ‘Waste’,
‘Terrestrial Ecosystem’, ‘Hydrosphere’, ‘Transport’ and ‘Lightning’) and N (reduced and oxidized) deposition
both national and transboundary. Output flows are represented by N deposition to national ecosystem
(hydro and terrestrial) and exported to boundary countries.
2.2 Nitrogen deposition definition
Nitrogen deposition is the term used to describe the input of reactive nitrogen species from the
atmosphere to the biosphere. Most concern has addressed the impacts of nitrogen deposition to terrestrial
ecosystems, but impacts may also occur in the marine environment. The pollutants that contribute to
nitrogen deposition derive mainly from nitrogen oxides (NOX) and ammonia (NH3) emissions. In the
atmosphere NOX is transformed to a range of secondary pollutants, including nitric acid (HNO3), nitrates
(NO3- ) and organic compounds, such as peroxyacetyle nitrate (PAN), while NH3 is transformed to
ammonium (NH4+). Both the primary and secondary pollutants may be removed by wet deposition
(scavenging of gases and aerosols by precipitation) and by dry deposition (direct turbulent deposition of
gases and aerosols) (Fowler et al. 1989, Hornung et al. 1995).
For assessment of effects it has been assumed that nitrogen originating from NH3 or NOX has the same
ecological effect (Sutton and Fowler 1993, Hornung et al. 1995). This assumption is now being challenged,
as both UK wide survey work (Stevens et al, and manipulation studies (Sheppard et al 2008) have found
stronger correlations between detrimental effects on semi-natural plant species, particularly among lower
plants, and the concentration or dose of reduced N. However, it is clear that NOX emissions are much more
widely dispersed than NH3, with the latter often deposited in high quantities to semi-natural vegetation in
intensive agricultural areas. Reduced N (Nred) is primarily emitted from intensive animal units and more
recently vehicles with the introduction of catalytic converters. Thus effects of NH3 are most common close
to urban highway and roadside verges, and within 1-500m of the point source depending on the size of the
source of the source. Aerosols of ammonia, by comparison, are carried much further and contribute to wet
deposition. The loading of N in wet deposition will depend on the amount of precipitation and the amount
of N. In the east, N concentrations can be quite high due to the low rainfall, whereas in the west the rainfall
is much higher but the concentrations tend to be lower.
Transboundary air pollution is a particular problem for pollutants that are not easily destroyed or react in
the atmosphere to form secondary pollutant. These are cross boundary pollutants that can be generated in
one country and felt in others; these require international actions and collaboration to control their
formation and effects. Transboundary air pollutants can survive for periods of days or even years and can
be transported 100s or thousands of miles before they affect the air we breathe, soils, rivers, lakes and/or
our food.
Transboundary nitrogen deposition for a single country is considered like the balance between
nitrogen input for other countries and nitrogen output towards other countries. This balance is
very sensitive to climate conditions and to geographical position.
Figure 2 -Time trend for reduced nitrogen deposition (A) or oxidized nitrogen deposition in comparison with total
nitrogen deposition in Europe, source EMEP.
In Figure 2 time trends for reduced (A) or oxidized (B) nitrogen deposition for total Europe are expressed in
comparison with total nitrogen deposition. The trend is generally decreasing for total nitrogen and oxidized
nitrogen deposition, whilst is more or less stable for reduced part of nitrogen deposition. This is linked, as
will be more detailed described lather, to the emission from agricultural sector, that is the main responsible
for reduced nitrogen deposition.
Figure 3 -. Percentage of Nitrogen reduced (black bars) or Nitrogen oxidized (white bars) deposition respect to the
total deposition (year 2010).
Figure 3 focus on the different composition of nitrogen deposition in terms of oxidized or reduced
components in the year 2010 for the European countries. Some countries show higher levels of the reduced
component of nitrogen deposition, that reach a value ranging between 80% in Ireland (IE) or 70% in
Netherland (NL).
2.3 Nitrogen pollutant definition
The pollutant emissions to be considered in this pool are ammonia (NH3), nitrogen oxides (NOX) and
(nitrous oxide) N2O.
Nitrogen oxides (NOX) are a generic term for mono-nitrogen oxides (nitric oxide, NO, and nitrogen dioxide,
NO2) and are mainly emitted during fuel combustion especially at high temperature. The main emitting
sectors are industrial facilities and road transport. NOX contribute to acid deposition and to eutrophication
of soil and water. Of NOX chemical species, NO2 is associated with adverse effects on health: high
concentrations cause inflammation of the airways and reduced lung function. NOX also contribute to the
formation of secondary inorganic particulate matter and tropospheric (ground-level) ozone (O3) with
associated climate effects.
Ammonia (NH3) contributes to both eutrophication and acidification. The vast majority of NH3 comes from
the agricultural sector in connection with activities and practices such as manure storage, slurry spreading
and the use of synthetic nitrogenous fertilizers. It is normally encountered as a gas with a characteristic
pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by
serving as a precursor to foodstuffs and fertilizers.
Nitrogen (N) compounds, emitted as NOX but also as NH3, are now the principal acidifying components in
our air and cause eutrophication of ecosystems (EEA, 2013a).
Nitrous oxide (N2O) is a powerful greenhouse gas produced both naturally and via human activities. N2O
gives rise to NO on reaction with oxygen atoms and this NO then reacts with ozone. So it is the main
naturally occurring regulator of stratospheric ozone. According to the Environmental Protection Agency
(EPA, 2013), it has a global warming potential (GWP) 310 times than carbon dioxide (CO 2). The main human
sources of N2O is agriculture, and especially soil cultivation, nitrogen fertilizers, and livestock production.
Natural sources of N2O are dominated by temperate and tropical soils and oceans.
The NH3, NOX and N2O input emission to the Atmosphere should be quantified from the output of the
subpools “Industry and Energy”, “Agriculture” considering emissions from livestock and nitrogen fertilizers,
“Transport”, “Waste” and “Sewage” sectors and natural emissions.
Emissions are usually quantified as tons of the emitted pollutant, while in a nitrogen budget emissions have
to be reported in tons of Nitrogen emitted. To convert pollution emissions in N emissions the coefficient to
be used is linked to the atomic weights of the different substances, as reported in table 1.
Table 1 – Coefficient to convert air pollution emitted (NH3, NOX, N2O) in N emissions.
From Substance
To N emissions
Conversion coeff
NH3 (weight 17)
N (weight 14)
0.824
NOx (as NO2 emissions: weight 46)
N (weight 14)
0.304
N2O (weight 44)
N (weight 14)
0.318
Looking at the conversion coefficient, this means that from 1 tons of NH3 more N is emitted in the
atmosphere.
Another important NOX source is lightning in the middle and upper troposphere. The knowledge of the
lightning-induced nitrogen oxides (LNOX) source is important for understanding and predicting the nitrogen
oxides and ozone distributions in the troposphere and their trends, the oxidizing capacity of the
atmosphere, and the lifetime of trace gases destroyed by reactions with OH (Schumann and Huntrieser,
2007). In the middle and upper troposphere, where NOX is long-lived and typically at more dilute
concentrations, LNOX is a particularly significant source (Ridley et al., 1996; Huntrieser et al., 1998;
Pickering et al., 1998; Zhang et al., 2000, 2003; Bond et al., 2001, 2002). Lightning is a transient, highcurrent electric discharge over a path length of several kilometers in the atmosphere (Uman, 1987). The
majority of lightning in the Earth’s atmosphere is associated with convective thunderstorms (MacGorman
and Rust, 1998; Rakov and Uman, 2003). Lightning forms from the breakdown of charge separation in
thunderstorms.
The global LNOX source is one of the largest natural sources of NOX in the atmosphere (Galloway et al.,
2004) and certainly the largest source of NOX in the upper troposphere, in particular in the tropics (WMO,
1999).
3
Inflows and outflows
The main input flows to the Atmosphere pool are the atmospheric import of Nr, as well as emissions from
all other pools in a National Nitrogen Budget.
This section describes generic methods for estimating the amount of various N inputs to the Atmosphere
pool.
3.1
Emission sources
In EU27 NOX emissions have dropped considerably since 1990 and a reduction of 48% in 2011 has been
observed (EEA, 2013b). Main reductions have been taken place in the electricity/energy generation sectors
as a result of technical measures and fuel switching from coal to gas.
NH3 emissions decreased considerably (-28%) from 1990 to 2011 as a result of improved manure
management even if in the last years the trend emission is quite stable (EEA, 2013b).
All detailed data are available at the following link http://www.eea.europa.eu/data-andmaps/data/national-emissions-reported-to-the-convention-on-long-range-transboundary-air-pollutionlrtap-convention-7
Figure 4 – EU27 NOX and NH3 emission trends from 1990 – 2011 (EEA, 2013c).
Figure 4 shows the contribution to total EU-27 emissions made by the aggregated sector groups.
For NOX, the main emitting sources are the energy and transport sectors. The road transport sectors
represent the largest source of NOX emissions, accounting for 40 % of total EU-27 emissions in 2011 (EEA,
2013c).
For NH3, the agricultural sector is responsible for the 93% of total EU-27 emissions in 2011 (EEA, 2013c).
Figure 4 – EU27 NOX (left) and NH3 (right) emissions by sector at the year 2011 (EEA, 2013c).
Nitrous oxide is naturally present in the atmosphere as part of the Earth's nitrogen cycle, and has a variety
of natural sources. However, human activities such as agriculture, fossil fuel combustion, wastewater
management, and industrial processes are increasing the amount of N2O in the atmosphere. Nitrous oxide
molecules stay in the atmosphere for an average of 120 years before being removed by a sink or destroyed
through chemical reactions. The impact of 1 pound of N2O on warming the atmosphere is over 300 times
that of 1 pound of carbon dioxide.
In EU-27, N2O emissions decreased by 36% in 2011 respect to the year 1990 (EEA, 2013d). Detailed data for
each Member States could be downloaded at the following link http://www.eea.europa.eu/data-andmaps/data/national-emissions-reported-to-the-unfccc-and-to-the-eu-greenhouse-gas-monitoringmechanism-7
Lightning and corona discharge during thunderstorm events cause atmospheric chemical reactions to take
place at high voltages and high temperatures. These reactions cause the production of NOx in the
atmosphere. Global NOx production by lightning has been estimated in the range of 3–5 Tg N/yr (Levy et
al., 1996). The methodology to estimate emissions from lightning could be found in the last versione of the
EMEP/EEA air pollutant emission inventory guidebook 2013 (EEA, 2013e) and on the web site
www.euclid.org .
3.1.1 Suggested Data Sources
Anthropogenic and natural emission sources of NOX and NH3 can be estimated from the EMEP/EEA air
pollutant emission inventory guidebook (EEA, 2013e).
At the link of the Center on Emission Inventories and Projections, http://www.ceip.at/, emission data
officially submitted by the Parties to the Convention on Long-Range Transboundary Air Pollution (CLRTAP)
can be downloaded.
The quantification of anthropogenic N2O emissions can be estimated from the IPCC guidelines for National
Greenhouse Gas Inventories (IPCC, 1997, 2006). From the UNFCCC site it is possible to download emission
data, http://unfccc.int/ghg_data/items/3800.php
Data can be downloaded for Europe on the
http://www.eea.europa.eu/data-and-maps#tab-datasets
3.2
European
Environmental
Agency
link:
Nitrogen deposition
Air dispersion models are used to provide an estimate of a concentration or deposition of a pollutant
emitted from an industrial process (point source) or a road (line source). Output from dispersion models
are often used to predict the contribution of a new or existing process, to level of pollutants at specified
points. The modeled outputs of concentrations and depositions can then be compared with environmental
limits (e.g. Critical Loads) and human health air quality limits. There are numerous models that are used for
both short-range local scale modeling (<20 km), and long-range, regional/trans-boundary, air pollution
(>50km).
Meteorological conditions have a significant effect on air concentrations and depositions of pollutants,
controlling their transport, diffusion and dry and wet removal. Large reductions of NOx depositions were
achieved during the 1990s in parts of Europe, especially for Germany, Czech Republic and the eastern
European countries such as Estonia, Lithuania, Latvia, Ukraine and Bulgaria. In total the reduction of NOx
emissions for the period 1990 to 2010 in the EMEP area amounted to -43%. The largest reductions of
ammonia took place in the eastern European countries after 1990, where emissions went down by nearly
50%. For other countries, emission reductions have been small, in the order of 10%. Compared to 1990,
the total decrease of NH3 emissions in the EMEP area amounted to -30% in 2010.
Transboundary nitrogen deposition are evaluated according to the country to country blame matrices. The
matrices are available in EMEP at the following link:
http://www.emep.int/mscw/SR_data/sr_tables.html
Nitrogen deposition per ecosystem type (cropland or forestland) can be determined following the
distribution of ecosystems that can be found in CORINAIR landcover, containing information of the
coverage and land use all over Europe (www.eea.europa.eu).
3.2.1 Suggested Data Sources
http://www.emep.int/mscw/index_mscw.html
http:// www.eea.europa.eu/data-and-maps/data/corine-land-cover
4
Uncertainties
As highlighted in the previous paragraphs, the LNOX source rate is considered to be the least known one
within the total atmospheric NOX budget. The global LNOX amount cannot be measured directly, and is
difficult to determine. In the last years many progresses have been made which allow reducing the
uncertainty of the global LNOx value, for example satellite observations of global, satellite observations of
NO2 column distributions, improved global models.
Major uncertainties in emission estimates seem to be related to activity data or emission factor knowledge.
National inventory report usually contains an estimation of emission uncertainties. About N deposition
modeling, the uncertainties is linked to the model itself and on the quality of data that feed the model.
Generally the uncertainties are strictly linked to the selected model resolution, thus a national based model
is to be preferred to an European one.
5
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6
Document version
This is a first version. For questions or comments please contact
Alessandra De Marco
alessandra.demarco@enea.it
Ilaria D’Elia
ilaria.delia@enea.it