Air quality expert group - Fine particulate matter (PM2.5) in ... - Defra

PM2.5 in the UK
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15. Some of the characteristics of local-scale models are summarised in A2.8 to
A2.10. All of these models are capable of predicting concentrations down to a
scale of a few metres or so and are driven by inventories on a more local scale,
such as the National Atmospheric Emissions Inventory (NAEI) or the London
Atmospheric Emissions Inventory (LAEI). Unlike the regional models, they do
not attempt to treat explicitly the formation of secondary particulate matter at
a regional scale but use assumptions based on measurements or the outputs
from other models as boundary conditions. For example, when considering a
specific urban area, the relatively large regional component and its speciation
are separately estimated and the increment due to explicitly modelled urban
sources added to it. Nevertheless, as shown in A2.8 and A2.9, it is possible to
disaggregate the contributions to PM2.5 to a high level of detail. In addition, the
ADMS-Urban model described in A2.10 is capable of producing both highly
time- and spatially-resolved predictions of PM2.5 mass (hourly predictions at
a 1 m resolution). Furthermore, these models can provide useful information
on urban transects, as shown in Figure 5.6 which reveals the importance of
the large regional component of PM2.5, the overall urban increment and the
importance of individual roads.
Table 5.1: A survey of the principal models employed to address PM2.5 in the UK.
Annex Model Institution Model type Scale
A2.1 WRF/CMAQ/AEA AEA Technology Eulerian grid Regional/UK
A2.2 WRF/CMAQ/CAIR University of
Hertfordshire
Eulerian grid Regional/UK
A2.3 WRF/CMAQ/KCL King’s College London Eulerian grid Regional/UK
A2.4 NAME Met Office, Exeter Lagrangian Regional/UK
A2.5 EMEP4UK University of Edinburgh Eulerian grid Regional/UK
A2.6 PTM rdscientific, Newbury Trajectory Regional/UK
A2.7 FRAME CEH, Edinburgh Trajectory UK
A2.8 PCM AEA Technology Semi-empirical/
Gaussian
A2.9 BRUTAL and UKIAM Imperial College
London
A2.10 ADMS-Urban CERC, Cambridge Gaussian plume/
Trajectory
5.3 What do models predict across the UK?
UK and local
Gaussian/Trajectory UK and local
(BRUTAL)
Regional (UKIAM)
Urban and local
16. Figure 5.1 shows the annual mean background PM2.5 concentration for 2009
(µg m -3 , gravimetric) estimated with the PCM model and Figure 5.2 gives an
equivalent map using data from the UKIAM model for 2010 (maps for 2020
are also shown and discussed later in Section 5.6). Both models show similar
spatial patterns in general with concentrations increasing from the north-west
of the UK to the south-east, however, there are differences in detail of up to a
few µg m -3 . Background concentrations in south-east England are greater by
more than a factor of two than over much of Scotland and Northern Ireland.
Superimposed on the general pattern are local maxima due to emissions from
major urban areas and arterial roads.