Mixed externalities - the green credentials of wood pellets

The complexity of environmental policy is laid bare in this investigation into the green credentials of burning wood pellets as an a energy source.

This BBC article reveals that the production of biomass generates air pollution, its classification as renewable is open to question and it's also less efficient that burning gas for example.

"Yet biomass is actually even more polluting than coal. Burning wood for energy produces at least as much carbon dioxide as burning coal per unit of energy produced and usually more"

End-to-end, do they deliver less carbon or are they another exercise in greenwashing?