Emissions from burning biomass
In the overall picture, biomass is almost entirely neutral with respect to CO2 emissions. Plants live and die. Their corpses on the forest floor slowly oxidize, producing CO2 in the exact amount that produced the plants in the first place. However, in some places such as peat bogs, the bottoms of lakes and oceans and dry landfills, biomass does not oxidize. Therefore, the net effect of plant life is slowly to reduce the CO2 concentration of the atmosphere. Burning biomass, however, returns all of the carbon to the atmosphere.
Burning biomass, however, is not as clean as letting it oxidize slowly. It is well known to gardeners that fertilizer contains nitrogen, which is necessary for production of chlorophyll. That nitrogen becomes various oxides of nitrogen (NOx, a.k.a. NOX, mostly NO2) when burned. For example, Southern California Electric is required to buy biomass-generated electricity from the Colmac station on the Cabazon Indian Reservation which burns agricultural waste for over 13¢/kWh. In 2000, it produced 369 GWh (giga-watt-hours) of electricity in 2000, emitting 215 tonnes of NOX in the process. That amounts to 0.58 tonnes of NOX per GWh.
On the average, biomass-burners produce 0.60 tonnes of NOX per GWh, as compared with 1.03 tonnes of NOX per GWh for the generic natural-gas plant. Modern combined-cycle (co-generation) units produce less than 0.05 tonnes of NOX per GWh.