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

PM2.5 in the UK
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inorganic particles from industries such as quarrying which are not accounted
for in the source profiles input to the CMB and which are therefore a significant
omission from the latter model. One of the other major differences is in the
secondary organic fraction, which in the case of the Yin et al. (2010) model
is derived by difference from the primary sources and is in close agreement
with that estimated by the elemental carbon tracer method; in the case of the
PCM, however, it is calculated by an off-line model which may not accurately
describe the very complex physico-chemical processes involved in secondary
organic aerosol formation, in particular the partitioning of secondary organic
species between the gas and condensed phases. However, the use of different
averaging periods may also be important, as for secondary inorganic particles.
Table 4.6: Comparison of PM2.5 source apportionment by receptor modelling (CMB) and
PCM model.
Category PCM CMB (Yin et al., 2010)
Mass (µg m -3 ) % Mass (µg m -3 ) %
sea salt 0.66 4.7 0.78 6.7
secondary
– inorganic a
– organic
traffic (exhaust, brake and
tyre wear)
4.31
0.85
30.7
6.0
5.10
1.66
43.9
14.3
2.26 b 16.1 1.51 c 13.0
soil and dust 1.90 d 13.5 0.85 e 7.3
off-road/smoking engines 0.93 f 6.6 1.13 g 9.7
industry/commercial/
domestic
1.93 h 13.7 0.21 i 1.8
other/residual j 1.22 8.7 0.39 3.4
Total 14.06 100 11.63 100
Notes:
a. Comprises ammonium nitrate, fine sodium nitrate and ammonium sulphate.
b. Includes traffic exhaust, brake and tyre wear and half long-range transported primary PM.
c. Comprises diesel and gasoline emissions including non-exhaust fine particles.
d. Comprises urban and rural dust categories.
e. Comprises dust/soil and vegetative detritus categories.
f. Off-road vehicle emissions.
g. Smoking engine category.
h. Sum of industry, commercial and domestic categories and half long-range transported primary PM.
i. Sum of natural gas, coal and wood combustion aerosol.
j. Unaccounted for by model.
Note: Long-range transported primary PM in the PCM model output is assumed to be 50% from road traffic and 50% from industry/
commercial/domestic emissions.