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

Organic carbon (µgm -3 )
12.0
10.0
8.0
6.0
4.0
2.0
Elemental carbon (µgm -3 )
PM2.5 emissions and receptor modelling
PM2.5 – BCCS y = 0.65x
0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Figure 4.8: Relationship of organic carbon to elemental carbon in the PM2.5
fraction at the Birmingham City Centre site (BCCS) (urban centre) showing the
minimum ratio line.
4.6 Receptor modelling sources of PM2.5 in the UK
79. Two generic methods of estimating the contributions of different sources to
concentrations of particulate matter in the atmosphere are available as follows:
(a) Dispersion modelling and chemistry–transport models both start with
spatially-disaggregated emissions inventories, from which concentrations
of unreactive primary pollutants can be estimated by dispersion modelling.
Modelling different sources or source types individually will give an estimate
of the contribution of that source to airborne concentrations. Where
distances of more than a few kilometres from source are involved, models
of atmospheric transport in either a Lagrangian or Eulerian framework are
more appropriate than simple dispersion models. For secondary pollutants,
or pollutants that undergo chemical reactions in the atmosphere, it is
necessary to use chemistry–transport models which combine dispersion and
advection of pollutants with chemistry and deposition schemes, allowing an
estimate of concentration as a function of location and altitude.
(b) Receptor modelling methods use measured atmospheric concentrations
of chemically-speciated particles to infer the sources responsible for their
emission or the pathways of formation of secondary pollutants. There are
essentially two main types of receptor models, those based on multivariate
statistical methods and those using a chemical mass balance approach
(described in more detail in Section 4.5 above).
80. The Pollution Climate Mapping (PCM) model used extensively in the UK to inform
policy is a hybrid of the two approaches. It uses measured airborne concentration
data as the basis for estimating concentrations and source contributions for certain
types of particles, and also dispersion modelling to estimate the contributions from
primary sources. It is described in detail in Chapter 5.
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