§ Mr. Lindsay HoyleTo ask the Secretary of State for Environment, Food and Rural Affairs what assessment she has made of the environmental impact of(a) burning wood as a fuel and (b) increasing the use of wood as fuel. [101292]
§ Alun MichaelBurning of wood from sustainably managed forests for energy production does not contribute to the UK's carbon dioxide emissions as the gas released through combustion will be absorbed by new tree growth. Wood combustion does contribute to the UK's emissions of methane and nitrousoxide. These gases have a global warming potential, but even when this is taken into account, the overall impact, in terms of greenhouse gas emissions per unit of energy input, is unlikely to exceed 15 per cent. of the impact of fossil fuel combustion for wood burnt domestically in open grates, or 5 per cent. of the impact of fossil fuel combustion for wood burnt in combustion plant.
Emissions associated with the management, harvesting and transportation of wood are small relative to total energy content of the wood. Nevertheless minimising transportation distances and improving the 508W efficiency of transportation should be included as factors in the evaluation of proposals for new wood fuel developments.
The combustion of wood, as opposed to coal or oil, produces low emissions of sulphur dioxide as wood has a lower sulphur content. Wood also tends to be burnt at lower temperatures than coal or oil which, in general, results in lower emissions of oxides of nitrogen compared to those from other fuels. Burning wood can also produce small amounts of benzene, particles, lead and polycylic aromatic hydrocarbons. Estimates of emissions of the main air pollutants from domestic and industrial wood combustion, compared with the UK totals, are set out in the Appendix.
Depending on the soil in which the biomass is grown, wood can contain heavy metals which on burning are retained in the ash. Inefficient burning can leave some carbon in the ash therefore polyaromatic hydrocarbons must also be considered. If concentration thresholds for either are exceeded, ash should be disposed of in a controlled manner. However a recent compilation of data on UK wood suggests that heavy metal concentration in ash will not constitute a hazard to human health or the environment. Since ash contains a range of important nutrients there is the possibility of returning it as a fertiliser to forests.
An overall assessment of the emissions impact from an increase in the use of wood as fuel depends on the fuel it replaces, the efficiency of the combustion systems and the abatement technology used.
Greater use of wood fuel can assist in limiting CO2 emissions, and other emissions can be minimised by maximising the efficiency of the combustion process, and by installing appropriate abatement control. Increases in the use of wood will be largely based on efficient and environmentally friendly systems 509W developed to meet stringent emission standards. Grant schemes introduced recently to encourage greater use of biomass specify highly efficient combustion and abatement systems.
Additional markets for wood will encourage more active management of forests which in turn will
Pollutant Unit Domestic Industrial National total Domestic as percentage of national total Industrial as percentage of national total Benzo[a]pyrene Kg 1,170 0.0518 10,800 10.8 0 Dioxins Grams 0.216 9.3 360 0.06 2.58 Cadmium Tonne 0.072 0.074 5.2 1.38 1.42 Mercury Tonne 0.027 0.074 8.5 0.32 0.871 Lead Tonne 0.82 0.037 496 0.17 0.007 Benzene Kilotonne 1.44 0.182 16.4 8.75 1.11 Carbon monoxide Kilotonne 89.3 5.23 4,170 2.14 0.125 Nitrogen oxides Kilotonnes 0.650 2.38 1,510 0.04 0.157 Particles (PMio) Kilotonnes 7.11 0.326 172 4.13 0.189 Sulphur dioxide Kilotonnes 0.0333 0.0274 1,170 0 0.002 Volatile organic compounds Kilotonne 4.87 0.594 1,680 0.29 0.035 Methane Kilotonnes 3.25 0.357 2,430 0.13 0.015 Nitrous oxide Kilotonne 0.0349 0.0511 141 0.02 0.036