Hi Don,

En-ROADS calculates energy generated PM2.5 emissions by multiplying an emissions factor (million metric tons emitted per exajoule by fuel source, expressed as MMT/EJ) by the annual rate of energy produced (EJ/Year by fuel source). The PM2.5 emissions factor (EF) for bioenergy is 0.04 MMT/EJ, less than that for coal, which is 0.12 MMT/EJ, but much greater than that for oil (0.005 MMT/EJ) and gas (0.0001 MMT/EJ). These EFs were estimated from an analysis by the International Institute for Applied Systems Analysis (IIASA). The EFs for coal, oil and gas were calculated using the GAINS model (IIASA) to estimate emissions/year from G20 countries/regions and then averaged. Countries included the United States, several EU countries, India (2 regions) and China (3 different regions). The EF for bio was calculated from the RAINS model (IIASA). Subsidizing or taxing bio indeed shifts the energy from bio and therefore the PM2.5 coming from it. However, the energy and therefore PM2.5 from other sources also changes due to shifts in the energy mix.

Additionally, since a greater fraction of coal is used for electricity than bio, and the thermal efficiency of these converting these fuels to electricity requires 3x the energy consumed, the difference in primary energy is greater than their difference in final energy.  What matters for PM2.5 emissions is the amount of energy required, i.e., primary energy, to meet the final energy demand. 

All the best,

Janet