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

PM2.5 in the UK
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provided by specific operators may be used. Emission-estimating methodologies,
emission factors and activity data are updated occasionally as further evidence
emerges that helps to improve our understanding of emissions and the factors
determining them, but a consistent inventory time series is always produced by
back-calculating emissions from previous years.
5. Emissions from fugitive dust sources are particularly difficult to estimate, but
occur as a result of many industrial and material handling processes. These
include iron and steel production and working, cement production, mining
and quarrying, construction and demolition, storage, handling and moving of
mineral products, and a range of agricultural processes.
6. Non-exhaust emissions of PM2.5 occur from road traffic, including tyre and brake
wear, and road abrasion. Emissions are estimated for all these processes, but are
highly uncertain. They are also unregulated sources, so emissions increase with
increasing traffic levels.
7. Resuspension of dust from road surfaces is not included as a source of PM2.5
in the inventory as it does not require reporting under CLRTAP. Studies have
shown that this source may make a significant contribution to atmospheric
concentrations of PM2.5 in urban areas (AQEG, 2005; SNIFFER, 2010), but it
is extremely difficult to quantify using traditional inventory approaches. The
contribution of resuspension of road dust to PM2.5 concentrations has usually
been estimated by modelling and source apportionment methods rather than
through emission inventories (e.g. by Grice et al., 2010, and Abbott, 2008).
For heavily-trafficked roads, it may be difficult to differentiate the contribution
of road dust resuspension from the contributions of other non-exhaust traffic
sources, such as tyre and brake wear emissions, but in more rural areas it may
be necessary to treat the resuspension of roadside dust in the wake of moving
vehicles explicitly as an additional source of airborne particulate matter (PM) in
models. The contribution of this source will depend on the silt loading of the
road surface and meteorological factors such as wind and precipitation.
8. Primary emissions of PM2.5 from natural sources such as wind-blown dust, sea
spray and biological material are not included in the inventory. Emissions from
accidental or natural fires in forests or crops are estimated by the NAEI, but are
not included in reported national emission totals.
9. In almost all cases, emission factors are expressed as mass emissions of total
suspended particulate matter (TSP) per unit of activity (e.g. fuel consumed,
distance travelled, tonnes output, etc.) or, at best, in terms of mass of PM10
emitted per unit of activity, and then fuel- and/or sector-specific PM2.5 size
fractions are applied to estimate PM2.5 emissions. The PM2.5 size fractions
represent the mass fraction of TSP or PM10 emitted as PM2.5 and are generally
taken from EMEP/CORINAIR emissions inventory guidebooks (EMEP, 2009),
USEPA sources (AP-42) 3 , industry experts or other literature sources.
10. Where applicable, emission factors take into account control measures for
the abatement of particulate matter emissions. For stationary sources, these
include regulations on industrial and combustion processes and dust control
measures covered under EU directives and national legislation as well as local
3 See http://www.epa.gov/oms/ap42.htm. AP-42: Compilation of Air Pollutant Emission Factors (USEPA).