Report from UK National Centre for
Integrated Assessment Modelling
27th TFIAM, Oslo, May 2002
Helen ApSimon, Tim Oxley, Teresa Gonzales, Tom Loh
& Ana Grossinho
Department of Environmental Science and Technology,
Imperial College, London SW7 2BP.
Report from UK National Centre for Integrated Assessment Modelling
May 2002
Helen ApSimon, Tim Oxley, Teresa Gonzales, Tom Loh & Ana Grossinho
Department of Environmental Science and Technology, Imperial College, London.
Introduction:
Following the move of Rachel Warren to the Tyndall Centre at the University
of East Anglia, Tim Oxley has joined the Integrated Assessment Unit at Imperial
College. Tim has previous experience in integrated modelling systems at Cranfield
University and the Spatial Modelling Centre in Kiruna, Sweden. We shall continue to
collaborate with Rachel at the Tyndall Centre, where she will be undertaking
development of integrated assessment models with a greater emphasis on climate
change.
At Imperial College we have continued to work on uncertainty analysis, but
the main emphasis has been on development of a UK scale integrated assessment
model, UK IAM, to consider effective strategies for reducing acidification and
eutrophication within the UK while at the same time meeting national emission
targets in accordance with the Gothenburg protocol. During this development further
work has been undertaken on particulate PM10 by Teresa Gonzales, with a prototype
UK scale model aimed at reducing particulate exposure alone. Another side aspect of
the UK IAM has been further studies of ammonia, with revision of UK cost curves,
and consideration of the geographical factors in introducing abatement. This work has
been undertaken by Tom Loh, another new recruit, who has combined his interest in
GIS with an updated version of MARACCAS as the start of his work in a larger
collaborative project on ammonia in the UK ( the NARSES project).
Uncertainty analysis
In previous work at the European scale we have undertaken sensitivity studies
with ASAM to see how the distribution of emission reduction across the different
countries changed in response to different transport patterns and uncertainties in
critical loads and cost curves. The effect of changing atmospheric transport was
examined by using source receptor relationships from years with contrasting
meteorology, or by stretching or contracting the deposition footprints of countries to
reflect uncertainties in the representation of atmospheric processes which could lead
to increasing or decreasing the range of transport before deposition. There were also
uncertainties about transport above the mixing layer, leading to “unattributable”
deposition.
As a continuation of this uncertainty and sensitivity analysis a preliminary
study is being undertaken to consider how results from ASAM may respond to the
advances at EMEP with the adoption of the Eulerian model. This overcomes the
problem of an unattributable portion, but also changes the pattern of atmospheric
transport. It should be noted that the Eulerian modelling does not extend over several
years as for the Lagrangian source-receptor modelling that has been used in IAM
prior to the Gothenburg protocol. The sensitivity study has therefore been undertaken
in a similar way to the sensitivity studies indicated above, by applying a multiplying
factor to each country’s deposition footprint based on the ratio of the Eulerian intercountry budgets to the corresponding Lagrangian budgets for the common year
analysed, and adjusting the unattributable. These ratios have been taken from the
EMEP report for 2001, which gives budgets from both models for the year 1996.
The deposition from the Eulerian model tends to be slightly higher than from
the Lagrangian model. Thus EMEP indicate that total deposition of sulphur in EMEP
countries is 9.3 Mtonnes (S) with the Eulerian model, and 7.0 Mtonnes with the
Lagrangian model. Corresponding figures for nitrogen are 8.8Mtonnes (N) compared
with 7.4 for the Lagrangian model. This means that the same gap closure is not
attainable in the two cases. However, as in previous studies we have compared the
allocation of emission reductions implied by the model across the different EMEP
countries assuming the same overall cap of expenditure while aiming to reduce
exceedance as much as possible. So far we have considered only acidification, taking
a total cap on expenditure of 6 billion euros, comparable with costs of SOx, NOx and
NH3 reduction in scenarios considered prior to the Gothenburg protocol (e.g. the G5/2
scenario).
Because, despite the overall increase in deposition, the relative contributions
of most countries remain rather similar, the distribution of effort is still very much the
same for many countries. The differences are larger than in previous sensitivity
studies, for example where we considered inter-annual variability using sourcereceptor matrices from different years: but significant differences still seem to be
limited to less than ten countries. In some of these there is a switch in the relative
emphasis on the different pollutants. Overall there appears to be a rather larger
emphasis on sulphur reduction, less on NOx, and around the same or slightly less on
NH3 reduction.
Development of a new Integrated Assessment Model for the UK, UKIAM
Integrated assessment modelling aims to bring together information on emissions,
atmospheric transport between sources and exposed areas or populations, criteria for
environmental protection , and potential emission control measures and their costs, in
order to explore effective abatement strategies. Based on experience at Imperial
College from development and application of the ASAM model, working in parallel
with the RAINS model of IIASA to support negotiations on the Gothenburg protocol
under the Convention on Long Range Transboundary Air Pollution (CLRTAP), work
has now begin on a new UK scale integrated assessment model, UKIAM, to
investigate strategies for attainment of national emission ceilings. Initially this is
focused on acidification, eutrophication, and particulate PM10.
The project is being undertaken in collaboration with associated activities within the
UK on emission inventories, atmospheric modelling, and mapping of critical loads. In
the initial version emissions are differentiated according to county of origin, instead
of to countries as in ASAM. However provision has been made to treat major point
sources individually in a subsequent version.
Atmospheric
transport
Emissions
Scenario analysis
Optimisation/
and ranking
Abatement
options& costs
Environmental
Criteria
Structure of UKIAM
Emissions
Initial development is being undertaken based on NAEI data for 1999 for SO2, NOx
and PM10, broken down by sector, and distinguishing major point sources. For
ammonia, emissions from CEH Edinburgh are being used, based on 1996 agricultural
census data. Further development will require projected emissions according to a base
case scenario reflecting current legislation up to 2010.
Atmospheric transport
As in ASAM this is based on source-receptor matrices representing the change in
annual deposition or concentration in any grid square due to a unit change in
emissions. Currently data has been provided for S and N deposition in each 5 by 5 km
grid square from calculations with the FRAME model at CEH Edinburgh, and for
primary particulate concentrations from the PPM model of IC. For S and N deposition
this data has been derived using reductions of SO2,NOx and NH3 in one county at a
time in line with average reductions of each required to attain the Gothenburg
protocol. (Checks will be undertaken to investigate the importance of non-linearity of
the response of deposition to emission reductions.) Deposition fields and sourcereceptor matrices are provided separately for forest ecosystems, heathlands and
grasslands, and as grid square averages to differentiate exceedance for different
ecosystem types with respect to both acidification and eutrophication. Prelimary S-R
data have also been provided from FRAME for secondary particulate SO4, NO3 and
NH4 concentrations. For primary particulates the PPM model is a straight line
trajectory model similar to FRAME and HARM, with 2 size classes (<2.5 and
between 2.5 and 10 microns). There is statistical treatment of dry and wet periods, but
as yet no allowance for orographic enhancement as in FRAME.
Environmental targets and exceedance functions
Environmental targets for acidification and eutrophication are based on critical load
data for different ecosystems provided by CEH Monkswood. In the initial version of
UKIAM, exceedance of critical loads for acidification for each ecosystem type has
been calculated as look-up tables for different combinations of S and N reduction in
each 5 by 5 km grid square. An equivalent approach is used for nitrogen deposition
alone with respect to eutrophication.
Environmental benefits of emission abatement are based on reductions in exceedances
with respect to acidification and eutrophication integrated over the UK; and for
particulates on population weighted concentrations as an indicator of population
exposure.
Abatement measures and costs
Information on abatement measures and costs are currently assembled in the form of
cost curves for each pollutant in each county. However provision has been made to
distinguish major individual sources, and treat these individually in future. It will also
be possible in subsequent versions to separate out measures that apply to more than
one pollutant e.g. to both SO2 and PM10. The advantage of using costs curves,
instead of a random list of measures, is that it reduces computing time in optimisation
mode by automatically ordering measures according to increasing unit cost. Transport
emissions are treated separately and reduced nationally (rather than in counties).
Other sectors can be separated out in a similar manner for regional or national
abatement.
Currently annualised costs and efficiencies are used, largely based on those used in he
RAINS model. The use of annualised costs could potentially be replaced by a
dynamic approach at a later date.
Scenario analysis and optimisation
UKIAM is designed to be run either in scenario mode, to examine the effect of
different emission scenarios, or to derive least cost solutions according to the data in
order to achieve convergence towards desired goals for environmental protection. The
scenario mode can be used to examine deviations from base line energy projections,
or agricultural scenarios- for example a low CO2 emission scenario to investigate
interactions between climate oriented strategies and acidification, eutrophication etc.
In the optimisation mode, a stepwise approach is adopted, successively cycling
through the available options and selecting that step which gives the highest ratio of
benefit to the cost of implementation. The benefit is calculated as a function of
reduced exceedance of the targets, defined in terms of the critical loads or population
exposure; different functions and weightings may be used to change the relative
emphasis on particular effects or protection of different ecosystems.
In the work for the UN ECE ASAM was largely used to examine various uncertainties
and investigate the robustness of different strategies. Inevitably in such a model there
are simplifications and uncertainties, and factors which are omitted. It is intended that
UKIAM should be used in a similar way, making use of the risk oriented approach
that has evolved from this experience.
Particulate PM10
During development of the UK IAM, work continued on particulate PM 10,
including a prototype model to investigate cost effective strategies to reduce
population exposure to primary PM10 from stationary sources in the UK. During the
course of this work a review was made of data from different sources on abatement
measures, their efficiencies and costs. It was clear that it was very important to have
good information on the current technologies employed as the starting point for
further reductions, and we are grateful to AEA Technology for making their
emissions data and cost estimates available. Unfortunately it was difficult to compare
the resulting UK cost curve with that produced by IIASA, because the latter starts
from unconstrained emissions rather than current technologies .
The AEA abatement data were then used in the IAM in combination with
atmospheric transport derived from the PPM model (previously used to supply
preliminary source-receptor matrices on the European scale for primary PM10), and
the UK emission inventory for primary PM10 on a 10 km grid. Major sources were
separated out for individual treatment, and the remainder treated on a sectoral basis.
The IAM aimed to optimise the reduction of population exposure, integrated across
the UK population, at minimum cost in accordance with the cost curve data.
The figure shows the resulting typical curve from the IAM, with an initial
section in which population exposure is reduced quite rapidly for moderate costs, a
middle section in which the improvement is increasingly more difficult, and a flat
section in which the remaining measures bring negligible improvement. The first most
cost effective steps imply measures for a range of sources- quarries, refineries, iron
and steel plants, cement plants and power stations; and technologies such as ESP,
fabric filters, fuel switching to natural gas, plus some potential but more uncertain
cheap measures to reduce quarry dusts. The order in which these steps are selected for
different sources also depends though on the location of sources relative to population
centres. The intermediate measures extend to a wider range of plants, and include
more efficient but more expensive measures. The last part of the curve implies a small
improvement from fitting FGD, though the main aim of this would be SO2 reduction
rather than particulates. This emphasizes the need to combine treatment of particulates
with that of other pollutants, as is the aim of the UK IAM.
Studies of abatement of ammonia emissions in the UK
In view of the shorter range transport and local deposition of reduced nitrogen
close to its origin, the geographical targeting of ammonia abatement in areas with
sensitive ecosystems can be very important . In the UK the NARSES (National
Ammonia Reduction Strategy Evaluation System) project was funded by MAFF (now
part of the Dept.of Environment, Food and Rural Affairs, DEFRA) to look at how and
where reductions in ammonia can be made at least cost. This project is led by ADAS,
the UK agricultural advisory service; and uses their detailed information about
farming conditions and practices across the UK, linked to GIS.
Meanwhile MARACCAS has been updated with revised cost data provided by
Martin Ryan, and applied to individual counties to provide county cost curves as input
to the UKIAM. There are some significant changes in estimated costs. For example
the original costs of equipment for slurry injection were substantially underestimated,
so that some of the application measures have become significantly more expensive
by factors of 2 or more. By contrast some other measures such as ventilation of
poultry housing, and revised ideas about covering slurry lagoons, have become
cheaper. Some measures have been rejected for application in the UK, including
scraper/sprinkler systems for dairy cow housing, and floating covers on slurry tanks.
There is also doubt about stopping the use of urea as a fertiliser as a viable measure.
This means that the maximum feasible reduction is a bit less than before. Another
change in UK data, not yet included in MARACCAS, concerns additional emissions
in the inventory from areas of hard standing on farms. Together with the contribution
from non-agricultural sources, raised at the TFIAM meeting in Brussels in 2001, this
enhances the gap between national emissions and the target set in the Gothenburg
protocol.
Preliminary studies have been undertaken of the contribution of ammonia to
exceedance of critical loads in the UK, and the effect of strategies to reduce it. The
MARACCAS county cost curves indicate maximum feasible reductions generally in
the range between 15 and 20% of agricultural livestock emissions. The heel points at
which marginal costs increase more sharply on the cost curves, or restricted sets of
measures that are easier to implement, give reductions more in the range up to 10%.
Clearly the localised deposition of ammonia close to the sources means that
geographically targeted strategies in sensitive areas are important for maximising the
environmental benefits, rather than imposing blanket measures across the whole
country.
Maps prepared using data from the UKIAM illustrate the relative roles of
deposition of oxidised nitrogen and reduced nitrogen in exceedance of nutrient
nitrogen critical loads (eutrophication), and the limited improvement possible from
abatement of ammonia emissions. Thus map (a) in the attached figure shows
accumulated exceedance based on emissions in 1996. Maps (b) and (c) show the
effect of removing all the oxidised and reduced nitrogen deposition respectively.
Oxidised nitrogen makes only a modest contribution, and clearly the reduced nitrogen
is far more important. However, (see figure d), cutting the reduced nitrogen by 20%,
consistent with a rather optimistic estimate of the maximum feasible reduction, has
only a limited effect in reducing exceedance, though similar to that in figure b
omitting 100% of the oxidised N. This still leaves major areas of exceedance.
a)
c)
b)
d)
Acknowledgments
This work has been supported by the UK Department of Environment, Food and
Rural Affairs, with additional contributions from PhD students and staff at Imperial
College. We are also grateful for collaboration from AEA Technology and the
information they have made available on PM10 emissions in the UK and on
abatement measures and costs.