| dc.description.abstract | Environmental applications of pyrogenic carbon, aka black carbon (BC), have
been hampered due to the poor characterization and quantification of environmental BC.
This dissertation was dedicated to the better characterization of environmental
char/charcoal BC (char-BC), the most heterogeneous and the less identifiable group in
the BC continuum. The analytical approach developed for char-BC was further
incorporated with other BC methods in environmental samples for a comprehensive
assessment of combustion-derived carbon inputs in different environmental systems.
The present study firstly evaluated the feasibility of using levoglucosan, a marker
derived from cellulose/hemocellulose combustion, to characterize and quantify char-BC
in the environment. Levoglucosan was found exclusively in BC materials derived from
biomass combustion albeit in highly variable yields across different char-BC. A further
examination of synthetic chars showed that temperature is the most influential factor
affecting levoglucosan yield in char. Notably, levoglucosan was only detectable in low
temperature char samples (150-350 degrees C), regardless of plant species. These results demonstrated that levoglucosan could serve as a good qualitative indicator for the
presence of char produced under low temperature conditions in soil, sediments, and
aerosols.
Results of lignin analysis on the synthetic chars further reveal that combustion can
greatly decrease the yield of the eight major lignin phenols with no lignin phenols
detected in any synthetic char produced at greater than or equal to 400 degrees C. The values of all lignin parameters
show significant shifts with increasing combustion severity (temperature and/or
duration), indicating that thermal alteration is an important abiotic lignin degradation
process. Hence the input of char-BC in the environments represents a terrestrial organic
matter source with highly altered lignin signatures.
Finally, a multi-proxy approach, including elemental (soot-BC) and molecular
(levoglucosan, polycyclic aromatic hydrocarbons (PAHs), and lignin oxidation products)
proxies, was adopted to investigate the centennial-scale temporal distribution of
combustion products in four sediment cores from Puget Sound basins, WA. The
observed temporal trends of soot-BC and combustion PAHs fluxes reflect the evolution
of energy consumption and the positive effects of environmental regulations. The
distinct temporal patterns of soot and PAHs among cores demonstrate that urbanization is
a crucial factor controlling the inputs of combustion byproducts to the environment. On
the other hand, the trends of levoglucosan may be more relevant to the climate oscillation
and thus show a regional distribution pattern. Our results demonstrate that environmental
loading of combustion byproducts is a complex function of urbanization and land use,
fuel usage, combustion technology, environmental policies, and climate changes. | en |
