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Grass near power plants reveals carbon dioxide truths 30/08/2016

New Zealand scientists have developed a way to use radiocarbon measurements to verify greenhouse gas emissions from power plants.

Radiocarbon researcher Dr Jocelyn Turnbull, of GNS Science, collecting data at Kapuni in Taranaki. The Kapuni gas-fuelled power station is in the background.

Radiocarbon researcher Dr Jocelyn Turnbull, of GNS Science, collecting data at Kapuni in Taranaki. The Kapuni gas-fuelled power station is in the background.

The new method, a world first, uses a novel sampling technique of collecting grass growing downwind of power plants, which faithfully records a measure of the carbon dioxide emitted from the power plant.

Developed by researchers at GNS Science, the method allows for the first time independent verification of greenhouse gas emission rates that have previously only been self-reported by power companies that use fossil fuels.

The research was published this week in the Proceedings of the National Academy of Sciences with the paper titled ‘Independent evaluation of point source fossil fuel CO2 emissions to better than 10%’.

Under the Paris Climate Agreement agreed on in December 2015, 195 countries including New Zealand agreed to reduce their carbon dioxide emissions.

“Our new technique provides a simple and inexpensive way to verify that companies and nations are actually doing what they have promised to do,” says lead author of the study, Dr Jocelyn Turnbull of GNS Science.

The researchers use a novel method which involves collecting grass samples downwind of a power plant.  The grass faithfully records the radiocarbon content of carbon dioxide from the atmosphere that the grass uses to grow.

Due to the extreme age of fossil fuels, carbon dioxide derived from combustion contains zero radiocarbon, whereas natural carbon dioxide sources contain high levels of radiocarbon.

By measuring the amount of radiocarbon present, the researchers are able to determine how much of the carbon dioxide at the location of each grass sample was emitted from the power plant.

They use wind data to translate the measured fossil fuel carbon dioxide concentrations at each location to the rate of emissions from the power plant.

It reduces uncertainties in the emission rate to less than 10%, an improvement over the current 20% using other more conventional methods, and sufficient to allow governments to verify the reported emissions.

This new research is the latest application of radiocarbon measurements that GNS Science and its predecessor, the DSIR, have been undertaking since 1951 at its Lower Hutt facility, the Rafter Radiocarbon Laboratory.  This Laboratory is the oldest continuously operating radiocarbon facility in the world.

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Background: Radiocarbon occurs naturally in all living things, and decays radioactively over time so that the time since death can be measured from the amount of radiocarbon – carbon-14 - remaining in the object being measured. Fossil fuels are so old that they contain no radiocarbon at all.

So carbon dioxide produced from fossil fuels contains no radiocarbon, and can be readily distinguished from naturally produced carbon dioxide, which has a ‘modern’ amount of radiocarbon.

Researchers at GNS Science are able to derive how much carbon dioxide in the atmosphere comes from fossil fuels, and from that they can work out carbon dioxide emissions from a power plant in tonnes per day.

The technique has been perfected during the past four years at the Kapuni Natural Gas Plant in Taranaki. The Kapuni plant has been ideal for the development of this technique for several reasons.

Firstly, plant operators have been very supportive throughout and have provided detailed emissions information on an hourly basis. Second, the plant is surrounded by farmland which eliminates potential distortions from urban or industrial sources.

Finally, the flat terrain and well documented weather at Kapuni have made it easy for scientists to model gas dispersion rates in the atmosphere.