Biodiesel effects on particulate radiocarbon (14C) emissions from a diesel engine

Abstract

The relative amount of 14C in a sample of atmospheric particulate matter (PM), defined as percent modern carbon (pMC), allows EPA to infer the fraction of PM derived from anthropogenic pollution sources. With increased use of biofuels that contain 14C, the main assumption of the two-source model, that 14C is solely derived from biogenic sources, may become invalid. The goal of this study was to determine the 14C content of PM emitted from an off-highway diesel engine running on commercial grade biodiesel. Tests were conducted with an off-highway diesel engine running at 80% load fueled by various blends of soy-based biodiesel. A dilution tunnel was used to collect PM10 emissions on quartz filters that were analyzed for their 14C content using accelerator mass spectrometry. A mobility particle sizer and 5-gas analyzer provided supporting information on the particle size distribution and gas-phase emissions. The pMC of PM10 aerosol increased linearly with the percentage of biodiesel present in the fuel. Therefore, PM emissions resulting from increased combustion of biodiesel fuels will likely affect contemporary 14C apportionment efforts that attempt to split biogenic vs. anthropogenic emissions based on aerosol-14C content. Increasing the biodiesel fuel content also reduced emissions of total hydrocarbons (THC), PM10 mass, and particulate elemental carbon. Biodiesel had variable results on oxides of nitrogen (NOx) emissions.