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

PM2.5 emissions and receptor modelling
background site in Birmingham. They used a thermal separation of organic
carbon from elemental carbon and were able to determine the radiocarbon
content of each. By making a number of assumptions, they were able to
disaggregate the carbonaceous component of the PM2.5 into the following
components:
• EC biomass, representing elemental carbon from the burning of wood and
other contemporary fuels.
• EC fossil, representing elemental carbon from the combustion of fossil fuels
predominantly in diesel engines but including, for example, industrial oil
and coal combustion.
• OC fossil, representing organic compounds derived from fossil fuel sources
and hence including emissions from road vehicles, but also of solventderived
compounds from industry and secondary particles derived from
them.
• OC biomass, representing organic carbon from the combustion of wood
and other biomass fuels.
• OC biogenic, representing primary organic carbon contained, for example,
in vegetative detritus, but also secondary organic carbon deriving from
biogenic precursors.
96. The average composition of the samples analysed by Heal et al. (2011) appears
in Figure 4.12 where it is compared with data from Zurich, Switzerland, and
Göteborg, Sweden. In Table 4.7, the masses of organic carbon reported for
the Birmingham sites have been converted to approximate masses of organic
matter, so as to give a breakdown of the carbonaceous aerosol based upon
the average concentration (over 26 samples) of total carbon of 5.00 µg m -3 in
the PM2.5 fraction. The rather low percentage attributable to the burning of
wood and other biomass tends to confirm the low contributions seen in the
results of Yin et al. (2010), but perhaps the most striking finding is the high
percentage attributable to biogenic organic carbon. Given the relatively modest
contribution of vegetative detritus shown by Yin et al. (2010) and seen in Figure
4.10, this is most probably largely secondary organic carbon, and it appears that
secondary organic matter (OM) from biogenic precursors makes a much larger
contribution to the overall total OM than secondary organic carbon from fossil
fuel precursors.
97. The work by Heal et al. (2011) to distinguish contemporary from fossil carbon
suggests that a large proportion of secondary organic carbon is biogenic in
origin (Table 4.7) and hence unlikely to decrease significantly in concentration in
the foreseeable future as it is unlikely to be subject to control measures.
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