EXPERIMENTAL AND TEMPORAL OBSERVATIONS ON THE OCCURRENCE AND ABUNDANCE OF PYROGENIC PAH RELATIVE TO ATMOSPHERIC OXYGEN LEVELS

The Phanerozoic record of atmospheric oxygen ([O₂]_atm) is derived from global geochemical cycles. Despite significant error margins, the record shows dramatic fluctuations throughout the Phanerozoic (Berner and Canfield, 1989). Because oxygen is critical to any fire, major fluctuations in [O₂]_atm may have significantly affected the frequency of biomass burning events, suggesting that wildfires would have been more prevalent at times of elevated [O₂]_atm (Scott, 2000). Fossil charcoal abundances qualitatively reflect this relationship. Although land plants had evolved by the Silurian, and the earliest true forests had evolved by the mid-Devonian, fuel accumulations and [O₂]_atm probably did not reach sufficient levels to sustain burning until the late-Devonian (Scott, 2000). By the Carboniferous, when [O₂]_atm had reached ~35% and fuel sources were plentiful (Berner and Canfield, 1989), fossil charcoal is globally abundant (Scott, 2000). In contrast, [O₂]_atm had fallen to ~15% by the Triassic, and fossil charcoal is nearly absent from the rock record (Scott, 2000). Based on the empirical association between [O₂]_atm and charcoal abundance, an implicit relationship between biomass burning and [O₂]_atm exists. By focusing on a distinct set of combustion-derived compounds, polycyclic aromatic hydrocarbons (PAH), the qualitative relationship can be approached quantitatively. During times of elevated [O₂]_atm, biomass-burning events are facilitated, and a greater proportion of PAH are expected. To test the relationship between [O₂]_atm and PAH production, PAH were extracted from modern, Carboniferous, and Triassic charcoals, relating to 21%, 35%, and 15% O₂, respectively (Berner and Canfield, 1989). The abundance of PAH extracted from these samples substantiate the relationship between modeled [O₂]_atm and PAH production. To better isolate the role of [O₂]_atm to PAH production, combustion experiments have been designed to generate PAH under various O₂ levels, different temperatures, and with different fuel loads. This design will help to isolate the roles of the three main combustion variables: O₂ level, fuel type, and temperature of burn. Multivariate statistical analyses will be conducted to establish the significance of correlations between PAH abundance and [O₂]_atm.