Pyrogenic carbon in a sedimentary record of the past 250 years

Pyrogenic carbon concentrations will be measured in two series of lake sediment samples, which will result in a high resolution record of PyC deposition of the past 250 years, thereby allowing reconstruction of pyrogenic carbon deposition over the industrial era. The aim of this study is to identify the sources of PyC in the sediment record and to characterize the type of PyC present in the samples, i.e. charcoal or soot.
It is planned to compare the down-core concentration of PyC to that of polycyclic aromatic hydrocarbons (PAHs), well defined products of incomplete combustion. PAHs are trace compounds specifically emitted from combustion processes and are found in the scale of ng g^-1 sediment (Lima et al., 2003; Elmquist et al., 2007). Data on bulk PyC concentrations would largely improve the quantification of combustion residue deposition. PAHs are formed concurrently with PyC and therefore the distribution of these two species should be closely related – an assumption that is however largely untested. We compare records originating from two different locations, a suburban (Pettaquamscutt River, RI, USA) and a remote site (Siskiwit Lake, MI, USA) with different resulting patterns of atmospheric deposition. To evaluate the influence of the emitting sources on the relationship between PAH and bulk PyC, at the industrially influenced Pettaquamscutt site will be compared with those of the a remotely located Siskiwit site, which predominantly receives atmospheric PyC input from wood used as domestic fuel.
Furthermore radiocarbon dating of the individual molecular markers will allow testing which forms of PyC (i.e. highly condensed and aromatic forms, compared to less condensed BC) in the sedimentary record stem from (radiocarbon dead) fossil fuel burning, and if other forms of PyC contain a larger proportion of derived from biomass burning - expressed by modern 14C contents. In any case will the data allow the construction of a molecular 14C record of deposited BC, giving a record of the relative proportion of fossil fuel-derived compared to biomass-derived BC since pre-industrial times.

 

References

Elmquist, M., Zencak, Z., Gustafsson, O., 2007. A 700 year sediment record of black carbon and polycyclic aromatic hydrocarbons near the EMEP air monitoring station in Aspvreten, Sweden. Environmental Science & Technology 41, 6926-6932.

Lima, A.L.C., Eglinton, T.I., Reddy, C.M., 2003. High-resolution record of pyrogenic polycyclic aromatic hydrocarbon deposition during the 20th century. Environmental Science & Technology 37, 53-61.