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

PM2.5 in the UK
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SIA components for future years. These projections were compared with PCM
scenario predictions made using the ESCs from the EMEP model. It was found
that the models gave broadly consistent results, with the NAME ESCs tending to
indicate a greater impact of change in emissions on concentrations than EMEP.
Comparison of maps of the ESCs showed a greater spatial variation in NAME.
33. Figure A2.4.1 shows an example of annual ESCs calculated by the NAME model
and demonstrates the non-linear effect on SIA components of a 30% emission
reduction in NH3 over the UK and Europe. The scale runs from -2.0 to 2.0,
where a value of 1.0 indicates a linear positive response, i.e. a reduction in the
primary pollutant leads to the same reduction in the particulate component. A
value greater than 1.0 indicates a greater reduction in particulate component
than in primary emission; conversely a sensitivity coefficient less than 1.0 but
greater than 0.0 implies a reduction in particulate component less than the
reduction in the primary pollutant. A negative emission sensitivity indicates
that the particulate component increases as the primary pollutant decreases.
In Figure A2.4.1, light orange shows sensitivity coefficients in the range -0.5-
0.0, orange in the range 0.0-0.5, red in the range 0.5-1.0, purple in the range
1.0-1.5 and blue in the range 1.5-2.0. The results from this work confirmed
the expected non-linear response of SIA components to emissions in primary
precursors and also highlighted considerable spatial variation in the response.
Figure A2.4.1: Annual average emission sensitivity coefficients calculated by the
NAME model, demonstrating the non-linear effect on PM ammonium, sulphate
and nitrate (from left to right respectively) of a 30% emission reduction in NH3
over the UK and Europe.
34. NAME model simulations of primary PM10 emissions have been undertaken to
establish the frequency and magnitude of potential transport of particulate
matter from the US to the UK. It was found that the maximum 24-hour mean
air concentration resulting from US emissions did not exceed 2.5 µg m -3 . The
annual mean was below 0.05 µg m -3 . It was concluded that it was unlikely
that US particulate emissions would make a significant contribution to a UK or
European pollution event.
35. The NAME model has been used to attribute particulate matter by country in
2003 using EMEP definitions of emission zones. For example, the top row of
Figure A2.4.2 shows the total annual average modelled PM10, annual average
PM10 originating from UK emissions, annual average PM10 originating from
French (FR) emissions and annual average PM10 from emissions from western