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Burning of biomass to generate electricity has risen rapidly in Europe, as a way to help companies and countries meet carbon emissions targets, despite worries about wider negative impacts on the environment.
If that sounds familiar, the European Union’s climate policies also favoured diesel over gasoline. Modern diesel cars are more fuel efficient, and so emit less carbon dioxide, but there have always been concerns over other pollution. The VW scandal showed that NOX emissions from diesel can be significant.
No-one is suggesting manipulation of biomass emissions data. But there are similar uncertainties and doubts about the impacts of burning biomass on emissions of particulate matter (PM), carbon dioxide (CO2) and NOX. The differences reflect a range of opinion, methodology and data, such as power plant efficiency and biomass source. It adds up to a muddy picture.
Taking these emissions in turn, there seems to be some agreement that co-firing biomass with coal (adding biomass to the furnace and substituting for some of the coal) can reduce emissions of larger particulate matter (PM). But it may also increase emissions of smaller PM2.5 (with a diameter below 2.5 micrometres), according to the “Clean Coal Centre” of the International Energy Agency (IEA). PM2.5 is the most dangerous air pollutant, contributing towards the millions of air pollution deaths worldwide. Because it is so small, PM2.5 can enter finer air passages of the lung, and from there the blood stream. It causes lung and heart diseases and strokes.
Given the academic uncertainty, I am tempted to go to the available data from one of the world’s s biggest coal and biomass-fired power plants, Drax. This is just one dataset, which I haven’t analysed in detail. Drax publishes data for its PM, NOX and CO2 emissions. It does not specify the size of PM, but I assume this to be PM10 (below 10 micrometres diameter).
Drax data show PM emissions steadily rising since the generator started burning more biomass and less coal. From 2010 to 2013, the company’s overall power generation fell very slightly (making this a useful control period), while its energy mix changed dramatically. Its coal and petcoke consumption fell 7 percent, and biomass consumption rose 75 percent. The same period saw particulate emissions rise 33 percent, and NOX fall nearly 3 percent (see figure below). Such data suggest that substituting biomass for coal increases PM emissions.
Studies suggest that substituting biomass for coal can reduce NOX emissions by around 10-20 percent. As we have seen, the Drax data do not support such a big reduction. NOX is a pollutant which contributes to surface level ozone, or smog, and respiratory illnesses.
The carbon emissions impact of burning biomass is perhaps the most difficult to measure, because of a time dimension. The benefit of burning biomass is only realised as replacement trees used to produce wood pellets absorb more CO2 as they grow. A recent study by the Natural Resources Defense Council (NRDC) calculated that it would take many decades for biomass made from whole trees today to become carbon neutral. But power generators such as Drax assume that their biomass is already carbon neutral. Drax shows that its CO2 emissions have steadily fallen since it switched to biomass, but only because it does not recognise CO2 emissions from burning biomass at all.
Biomass has hard to quantify impacts on CO2 and NOX, and may increase PM2.5 emissions. Nevertheless, it is supported under European carbon trading and renewable energy regulation. The sector is ripe for better clarity over the science and reporting of emissions, to avoid a more serious re-think on policy support.