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

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l<strong>in</strong>e and po<strong>in</strong>t sources. But the same treatment used <strong>in</strong> the PCM model has<br />

been adopted for secondary organic aerosol and other PM components not<br />

covered <strong>in</strong> the emissions <strong>in</strong>ventory and thus not directly modelled. Total PM<br />

concentrations are calculated for each 1 km x 1 km grid square by add<strong>in</strong>g all the<br />

different contributions for the appropriate size fraction, PM10 or <strong>PM2.5</strong>. Bear<strong>in</strong>g<br />

<strong>in</strong> m<strong>in</strong>d the uncerta<strong>in</strong>ties of future projections, the treatment of roadside<br />

concentrations is aimed at an overall statistical comparison with air <strong>quality</strong> limit<br />

values across the UK, rather than accurate projections at specific locations as for<br />

example <strong>in</strong> ADMS. Roadside enhancement factors for street canyon effects are<br />

related to population density and roadside concentrations are calculated for the<br />

road with the highest emission density <strong>in</strong> each grid square. Results from UKIAM/<br />

BRUTAL were submitted for the <strong>Defra</strong> model <strong>in</strong>ter-comparison exercise, show<strong>in</strong>g<br />

comparable performance with other models.<br />

Applications to modell<strong>in</strong>g of <strong>PM2.5</strong> and source apportionment<br />

65. Illustrative results on source apportionment of population-weighted mean<br />

concentrations are given below <strong>in</strong> Figure A2.9.1, with comparisons for the years<br />

2000 and 2020 to complement results given <strong>in</strong> Chapter 5.<br />

PWM Concentration (µg/m 3)<br />

14<br />

12<br />

10<br />

8<br />

6<br />

4<br />

2<br />

0<br />

Source-appotioned <strong>PM2.5</strong> concentrations for UEP30 scenarios (2000/2020)<br />

B2000 B2020<br />

aNO3<br />

SO4<br />

NH4<br />

Primary <strong>PM2.5</strong><br />

Pmwater<br />

SOA<br />

SeaSalt<br />

Iron dust<br />

Calcium dust<br />

Figure A2.9.1: Breakdown of <strong>PM2.5</strong> concentrations by component for 2000<br />

and 2020.<br />

A2.10: ADMS-Urban<br />

Annex 2: PM modell<strong>in</strong>g <strong>in</strong> the UK<br />

66. The ADMS-Urban model is described <strong>in</strong> Carruthers et al. (1998) and its<br />

treatment of <strong>particulate</strong>s <strong>in</strong> particular is covered <strong>in</strong> AQEG’s report on PM<br />

(AQEG, 2005). In essence the model calculates the concentration of PM as the<br />

sum of the calculated contribution from sources represented <strong>in</strong> an emission<br />

<strong>in</strong>ventory for the doma<strong>in</strong> of <strong>in</strong>terest and the rural background estimated<br />

from measured data or from a regional model(s). The transport and diffusion<br />

of PM emitted from the doma<strong>in</strong> of <strong>in</strong>terest is calculated us<strong>in</strong>g the ADMS<br />

dispersion algorithms for po<strong>in</strong>t, l<strong>in</strong>e, area and grid sources nested with<strong>in</strong> a<br />

171

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