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

PM2.5 emissions and receptor modelling
57. National emissions inventories such as the NAEI must follow prescribed
reporting guidelines defining what sources are and are not included, and what
methods and emission factors should be used to calculate emissions. Most
effort will therefore be expended in developing inventories that meet these
requirements. The significance of this as far as PM2.5 is concerned is that many
of the sources that make a significant contribution to ambient concentrations
of PM2.5 are not included in national inventories, e.g. road dust resuspension,
wind-blown dust and biogenic sources. There are no established methods for
quantifying emissions from these sources and traditional inventory methods
based on source-specific emission factors and activity datasets cannot be
used. Inventories for biogenic sources are not developed on a regular basis
as they are not required for national inventory reporting to the UNECE and
Intergovernmental Panel on Climate Change (IPCC). Although techniques for
estimating biogenic emissions from forests and grasslands are given in the
EMEP/EEA air pollutant emission inventory guidebook (EMEP, 2009), these
are not used to provide biogenic emission inventories for individual countries
by respective inventory agencies. Air quality models normally use methods
based on meteorologically-driven emission potentials to estimate the temporal
and spatial variability in biogenic emissions. Emission estimates are uncertain,
especially for individually speciated VOCs (isoprene and terpenes), and these
techniques are not frequently used to provide an overall estimate of national
NMVOC emissions from biogenic sources to compare with anthropogenic
sources on a regular basis.
58. Although national inventories for most anthropogenic sources may be
considered more reliable then inventories for natural sources, especially when
they involve only an annual emission rate, even these can be of variable quality,
consistency and completeness. Emission inventories reported by different
countries can also be of variable quality and this will be more pertinent to
models of PM2.5 than it might be for nitrogen dioxide (NO2) for example,
because of the strong influence of precursor emissions of PM transported over
a longer distance from different countries. There is a time lag of over a year
between when emissions are reported and the inventory year they refer to and
one question that can be asked is whether inventories for different countries
used in models even refer to the same inventory year.
59. The quality of inventories of ammonia emissions may become of increasing
concern in future years when it is considered how little NH3 emissions are
expected to change over time across Europe when compared with emissions for
other PM2.5 precursors, SO2, NOx and NMVOCs, as highlighted in Section 4.3.
The question then becomes how well and how consistently inventories for NH3
emissions are produced in the UK and other European countries; this inevitably
focuses attention on the key sources from agriculture. It is particularly difficult
to quantify agricultural emissions of NH3. A similar argument may apply to the
consistency and quality of inventories of SO2 and NOx from shipping, which will
become more dominant as a source of PM2.5 as emissions of these pollutants
from other sources diminish. Shipping emissions are not captured well in
national inventories and there will be an increased need to ensure consistent
emissions datasets are made available for modellers covering sea territories
across Europe.
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