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

PM2.5 emissions and receptor modelling
41. Emissions of these pollutants occur to varying degrees from stationary and
mobile combustion, industrial processes and agricultural sources. Many of the
European regulations and national legislation that control direct emissions of
PM also control emissions of these precursors, although the abatement options
are different for each pollutant. The Large Combustion Plants Directive and
IPPC Directive apply to NOx and SO2, while SO2 emissions are also influenced by
the Sulphur in Liquid Fuels Directive (1999/32/EC). Vehicle emission directives
limit emissions of NOx and NMVOCs from vehicle exhausts, though there is
evidence to suggest that these directives have not been effective in reducing
“real world” NOx emissions from modern diesel vehicles manufactured to
meet Euro III-V standards (Carslaw et al., 2011). The Fuel Quality Directive
(2009/30/EC) limits the volatility and sulphur content of transport fuels. The
Solvent Emissions Directive (1999/13/EC) limits emissions of NMVOCs due to
the use of organic solvents in certain activities and installations. Emissions from
shipping are controlled under the International Convention for the Prevention
of Pollution from Ships (MARPOL), which sets limits on the sulphur content of
marine fuels and NOx emissions from new engines. More stringent standards
are now controlling emissions from new aircraft engines. Further information on
legislation and abatement options for these pollutants can be found in previous
AQEG reports 9 and SNIFFER (2010).
42. Figure 4.6 shows the UK emissions of NOx, SO2, NMVOCs and NH3 from 1990-
2020. The figures are taken from the latest version of the NAEI, covering the
years up to 2009 (Passant et al., 2011), and projections up to 2020 based
on DECC’s UEP38 energy projections. Figure 4.6 also shows how precursor
emissions in the UK have fallen by varying amounts over the period from 1990-
2009, partly due to the varying contributions made by different sectors to
each pollutant. Emissions of NOx have fallen by 59% since 1990 due mainly
to reductions from road transport and combustion for power generation.
Estimations are on the basis of the current vehicle emission factors used in the
NAEI which have been brought into question. The NAEI is currently switching
to a new set of emission factors that are more in line with up-to-date evidence
on the efficiency of recent and current Euro standards for diesel vehicles.
When implementation is completed, this is likely to lead to a reduction in
the estimated rate of decline in UK NOx emissions over recent years. NMVOC
emissions have fallen by 70% since 1990, mainly due to reductions from road
transport. SO2 emissions have fallen by 89% since 1990, almost entirely due
to reductions in combustion emissions from the power generating industry.
Emissions of NH3 are dominated by agricultural sources and have only declined
by 21% since 1990.
43. As well as showing different trends over time because of differences in source
contributions, the PM2.5 precursor emissions also exhibit different spatial
patterns, as shown in Figure 4.7, for example, where NOx emissions are
dominant in major urban areas, and NH3 emissions occur predominantly in more
rural areas of England. The contribution of different UK precursor emissions to
ambient PM2.5 therefore varies spatially as well as having varied over time due to
the different trends in emissions of each precursor gas.
9 See http://www.defra.gov.uk/environment/quality/air/air-quality/committees/aqeg/publish/.
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