Factors influencing the stable carbon isotopic signature of methane from combustion and biomass burning

Factors controlling the delta(13)C of methane released by combustion includ e the combustion efficiency of the fire and the delta(13)C of the fuel. Smo ldering fires produced C-13-depleted methane relative to hot, flaming fires in controlled forest and grassland burns and within a wood stove. Pine for est burns in the southeastern United States produced methane which ranged f rom -21 to -30 parts per thousand, while African grassland burns varied fro m -17 to -26 parts per thousand, depending upon combustion phase. African w oodland burns produced methane at -30 parts per thousand. In forest burns i n the southeastern United States, the delta(13)C Of methane released with s moldering was significantly C-13 depleted relative to methane released unde r hot flaming conditions. Methane released with smoldering was depleted by 2-3 parts per thousand relative to the fuel delta(13)C, but this difference was not significant. The delta(13)C Of methane produced in a variety of wo od stove conditions varied from -9 to -25 parts per thousand and also depen ded upon combustion efficiency. Similar results were found for methane prod uced by gasoline automobile engines, where the delta(13)C Of methane varied from -9 to -22 parts per thousand. For combustion occurring within the con fining chamber of a wood stove or engine the delta(13)C of methane was clea rly C-13 enriched relative to the delta(13)C of the fuel, possibly because of preferential combustion of (CH4)-C-12 in the gas phase. Significant quan tities of ethylene (up to 25 to 50% of methane concentrations) were produce d in southeastern U.S. forest fires, which may have consequences for physio logical and reproductive responses of plants in the ecosystem. Methane prod uction in these fires varied from 0.2 to 8.5% of the carbon dioxide product ion.