Category Archives: Global change

GAUGE kicks off!

On the 1st March, we officially began our new £3m NERC-funded consortium project Greenhouse gAs Uk and Global Emissions (GAUGE). The University of Bristol press release explains:

Scientists awarded grant to determine UK’s greenhouse gas emissions
Press release issued 1 March 2013

Researchers in the University of Bristol’s Atmospheric Chemistry Research Group (ACRG), in collaboration with scientists around the country, have been awarded funding from the Natural Environment Research Council (NERC) to provide an independent ‘top-down’ check on the UK’s greenhouse gas emissions estimates.

GAUGE schematic
GAUGE will involve measurements of greenhouse gases from the air, sea and space in an effort to better quantify UK emissions

The UK is required to estimate how much climate-warming carbon dioxide, methane and nitrous oxide it emits each year. However, at the moment, these estimates rely heavily on so-called ‘bottom-up’ accounting methods that may be subject to biases and inaccuracies.

The GAUGE project (Greenhouse gAs Uk and Global Emissions) is a three and a half year collaboration between several universities and research institutions across the UK.

ACRG’s Professor Simon O’Doherty, who also runs the UK greenhouse gas monitoring network funded by the Department for Energy and Climate Change, said: “It’s important that we expand our greenhouse gas observation capabilities in this country, if we’re really going to understand what we’re emitting. But it’s equally important that we begin exploring new types of measurement, which may help us understand emissions processes more fundamentally.”

GAUGE will bring together a more comprehensive suite of greenhouse gas observations around the UK than has ever been compiled. The project will determine emissions using information from satellites, aircraft, tall towers (including the BT tower in the middle of London), balloons and boats.

In addition to developing new measurements, GAUGE will use computer models to simulate how greenhouse gases travel through the air.

Dr Matt Rigby, a research fellow at ACRG, said: “By measuring the concentration of greenhouse gases in the atmosphere, and then using computer models to simulate where the air came from in the days before the measurements, we can determine emissions from the surrounding areas. This new funding will allow us to develop these methods with the help of the Met Office and GAUGE partners at other universities.”

Using the new measurements and modelling techniques, GAUGE researchers hope to make the UK’s emissions amongst the best-quantified in the world.

Using new measurement technology to estimate methane sources

Delta-13C-CH4
MOZART simulation of 13C-CH4 in the atmosphere. The blue areas show parts of the atmosphere with a smaller fraction of the 13C-CH4 isotope than the atmospheric average, due to near-by emissions from microbial sources. In contrast, the red areas show air that is enriched in 13C-CH4, probably due to biomass burning.

Although methane is the second most important greenhouse gas its sources are quite poorly understood. However, new methods of measuring atmospheric methane may be able to help.

Methane is a molecule containing one carbon and four hydrogen atoms. These atoms usually have an atomic mass unit of 12 (carbon) and 1 (hydrogen). However, they also occur in higher masses in nature, called isotopes. Carbon-13 and deuterium (hydrogen with a mass of 2) occur in one atom for every few thousand atoms of regular carbon or hydrogen. This becomes potentially useful for us, because different sources of methane emit molecules with slightly different ratios of carbon-12 to carbon-13 or different ratios of hydrogen to deuterium. For example, methane emitted from wetlands has less 13C than the average in the atmosphere, whereas wildfires emit methane with a relatively high deuterium content.

So, by measuring methane concentrations and isotope ratios in the atmosphere, we can hope to learn something more about where the methane came from.

In the last few years, advances in laser spectroscopy have meant that we can now measure the isotopic composition of methane by shining lasers through a sample and measuring the absorption of certain wavelengths. However, the variations in methane isotope ratio that we expect to see in the atmosphere are very small. Therefore, to be able to resolve small changes, some people are proposing to also “pre-concentrate” air samples, which means that we remove a lot of the nitrogen, oxygen and other major components of air, to leave a more concentrated sample of methane that can be analyzed. Similar systems exist for measuring concentrations of other gases, but not yet for methane isotopes.

In this paper, we asked the question: “If we had these instruments at each AGAGE station, how much better would we be able to constrain methane emissions from different sources than we can at present?”. The answer we found was a little mixed. We found that these new measurements would provide additional information about the methane emissions to the atmosphere. However, the amount by which the uncertainties in our current estimates of methane emissions would be reduced is a little smaller than we hoped for. For example, for wetlands (the single largest source) and other microbial sources, we found that global uncertainty reduction would be reduced by only around 3%. For smaller sources that had a more “distinct” source isotope ratio such as biomass burning, larger relative uncertainty reductions were possible (9%).

Despite the relatively modest uncertainty reductions, my feeling is that, given the importance of methane in the global climate system, these new instruments will have a role to play in a future methane observing system. Given the complexity of the system, no single measurement (or modeling) strategy will be able to fully determine the causes of the strange changes we see in methane. However, by combining many measurement types, we should be able to understand the system better than we currently do.

Four new HFCs

Hydrofluorocarbons (HFCs) are replacements for chlorofluorocarbons (CFCs), whose use is being phased out because they are primarily responsible for depleting the ozone layer. While HFCs don’t destroy ozone, they are often very powerful greenhouse gases, so it is important that we monitor their concentration and emissions. One difficulty in doing this is that there are many HFCs emitted into the atmosphere, and new ones are appearing all the time.

To keep track of these gases, my colleagues in the AGAGE network have developed a system that can measure gas concentrations using mass spectrometry. The system is able to detect gases at very low concentrations, by removing most of the nitrogen and oxygen from the measured samples, increasing the concentration of the pollutants they want to measure. This means that we can now detect ‘new’ gases very soon after they appear in the atmosphere.

In this paper, Martin Vollmer from Empa in Switzerland describes the measurement of four HFCs that have appeared in the atmosphere over he last decade or so (HFC-227ea, HFC-236fa, HFC-245fa, HFC-365mfc). Using a combination of in situ measurements, and new measurements of archived air samples, we can determine the entire air history of the four gases, from the year they first appeared in detectable amounts.

Measured mixing ratios of four new HFCs

Using these observations, and a two-dimensional model of the atmosphere, we calculated the annual global emission rates. As is often the case, the emissions we found differed from inventory estimates by substantial amounts, highlighting the value of these sort of ‘top-down’ verification techniques.