Goodnight Earth

As politically divisive as hydraulic fracturing is, we still need much more data to determine its environmental effects before deciding if it can be major source of energy during our transition away from fossil fuels. Unfortunately, this lack of data apparently means that companies are able to begin large operations without knowing all the costs, due to a lack of regulations that should probably be there while more research is done.

This brings us to a new study published in PNAS that shows orders of magnitude larger methane emission from well pads at fracking sites that were not previously thought to be significant contributors to greenhouse gas emission.

Methane is a substantial greenhouse gas contributor.. It actually has about thirty times the global warming potential of carbon dioxide (CO2), but plays less of a role due to its smaller overall percentage in the atmosphere. But there has been a disturbing trend over the past decade of an increase in methane concentration in the atmosphere - thus the great importance in understanding when and where we are emitting it! In fact, if methane emissions are large enough, fracking may be on the same level as coal in terms of warming potential.

This study used an aircraft to fly over well pads and measure methane emissions from individual plumes coming from the pads. These flights occurred during June 2012 in southwestern PA, and they measured the flux of CH4 coming from each pad (measured in CH4/s, or CH4/s/km^2 if not integrated over a particular area).

This figure basically says it all - the orange dotted line is the sampling region where the aircraft measured methane emissions. The red circles and green and blue lines are measures of parts per million (ppm) of CH4 measured. Across the sampling region, a regional flux of 2-13 g CH4 /s/ km^2 was measured. The authors then integrated over distance and averaged across all the wells in the sampling region, and found a flux of 34 g CH4 /s per well, orders of magnitude beyond previous estimates.

What’s more surprising is that these wells had not even become fully operational - the companies were still drilling down to depth. Thus, these emissions are basically leaks during preparation that have previously been unaccounted for. Just to have it hit home, here’s another figure showing methane emissions as a function of horizontal distance vs altitude for several pads near Tau (see first figure):

 

Although I’m not an expert on this area of study, the authors appeared to be diligent about controlling for other possible sources of methane emission (although the figure above shows it’s clearly emitting from a ground source!). It’s hard not to be biased about fracking after seeing results like this - clearly we are moving way too fast and expanding fracking sites before we know what harm we’re doing. We just don’t have a good enough picture of what the long-term consequences are.

Reference

 

Caulton, D., Shepson, P., Santoro, R., Sparks, J., Howarth, R., Ingraffea, A., Cambaliza, M., Sweeney, C., Karion, A., Davis, K., Stirm, B., Montzka, S., & Miller, B. (2014). Toward a better understanding and quantification of methane emissions from shale gas development Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1316546111

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Anthropogenic climate change has become a household phrase, spreading throughout our culture as more and more research describes the effect of fossil fuel emissions on both CO2 levels in the atmosphere and average global surface temperatures. But our society’s CO2 emissions are part of a much larger carbon cycle that has existed for much longer than our species. The cycle involves, in one direction, the natural emission of CO2 from volcanic eruptions and outgassing from the Earth’s mantle, balanced in the other direction by the uptake of CO2 by the ocean and land.

The ocean uptake is well understood, as carbon dioxide dissolves in surface waters to create calcium carbonates, carbonic acids, and the like. The carbonates then slowly drop to the bottom of the ocean, leak into the Earth’s mantle, and are emitted again through eruptions and outgassing to complete the cycle. Our role as fossil fuel users can be seen above in the blue ‘fossil carbon’ line, as we dig into the crust and combust fossil carbons that have entered the soil eons ago as organic matter.

Terrestial carbon uptake, on the other hand, is a bit of a mystery. We know that it exists, but the science community has usually inferred it to be whatever is left over after taking into account ocean and human-directed mechanisms to balance the emission and uptake. However, a very cool, 10-year study has just appeared in Nature Climate Change that definitively shows the important role that arid environments play in carbon uptake. This is crucial information, as arid environments have largely been ignored in this capacity due to their lack of plant matter, relative to forested environments, that are usually considered to be the main actors in taking up carbon through photosynthetic processes. This information will be especially important as we begin to develop in more arid environments, as this will likely take away from the carbon uptake potential of these ecosystems and leave more of the CO2 sitting in the atmosphere.

This is the satellite view of of a plot of land used in the study. Nine such samples exist as part of the Nevada Desert Free-Air CO2 Enrichment Facility (NDFF, for less of a mouthful) in the Mojave Desert. Each site is 23 meters in diameter, and, over a ten-year period (1997-2007), three of each were exposed to three different CO2 fumigation conditions: 1) no fumigation; 2) ambient CO2 fumigation (current); and 3) CO2 fumigation matching the level expected to be in the atmosphere around 2050 (elevated).

After the ten years, biomass and soil were collected and their carbon content was measured. Significantly greater organic carbon was found in the elevated condition, demonstrating that the environment sucked up more organic carbon if more was in the surrounding atmosphere. This was mainly found in the soil and not in plants, which the researchers say contrast more fertile ecosystems, which show increased plant mass with increased atmospheric CO2. The research found that this increased carbon content in the soil was likely due to increased photosynthetic processes, as plants under elevated CO2 conditions almost double their photosynthetic rates.

This is one of the first studies to demonstrate significant carbon uptake in an arid ecosystem. These findings should stimulate more research on carbon uptake in unexpected terrestrial environments (i.e., non-forested) so we can begin to get a clearer picture of the exact mechanisms of terrestrial capture. This knowledge will be imperative as our civilization continues to expand into new territory, possibly cutting off more and more avenues of carbon uptake that will leave more CO2 in the atmosphere to expedite global warming.

Reference

 

Evans, R., Koyama, A., Sonderegger, D., Charlet, T., Newingham, B., Fenstermaker, L., Harlow, B., Jin, V., Ogle, K., Smith, S., & Nowak, R. (2014). Greater ecosystem carbon in the Mojave Desert after ten years exposure to elevated CO2 Nature Climate Change DOI: 10.1038/nclimate2184

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Tiny batteries for your cell phone or camera that can hold days of charge? Although it may seem like fantasy, this is the goal for researchers looking into new materials for lithium (Li) - ion batteries. Current state-of-the-art technology uses a graphite anode, which is the electrode in the battery where the Li is stored during charging of the battery and discharged during use. The capacity of the anode is a crucial quantity, as it relates to how much charge can be stored in the battery and used before needing to plug it in to recharge.

Capacity depends mainly on the chemistry and binding between the anode and the Lithium. Theroetically, silicon should have about ten times the capacity of graphite, however it’s been difficult for researchers to find a way to develop cheap silicon electrodes that don’t expand and break when charged with lithium. Fortunately, a recent study in Nano Letters has found a method to create anodes using nanoporous silicon very cheaply that limits volume expansion while providing greater capacity!

The researchers chose to use a metallurgical Si because of its cost ($1000/ton compared to $50,000/ton for nanoporous Si that is pyrolized at high temperatures. What’s metallurgical Si (I had to look it up too :))? Basically, silicon is naturally found on Earth with a significant portion of other metals. Metallurgical grade silicon is >98% pure Si, usually made by heating SiO2 to about 2000 C with some carbon material such as charcoal or coal.

The key process the researchers discovered was a method to create porous Si from the metallurgical Si as shown above. They did this as follows. They happened to have a metallurgical Si sample that was made of about one percent iron (Fe) and aluminum (Al) impurities (basically, this means Si atoms substituted by either Fe or Al about one percent of the time). They first ground the silicon into a fine powder, then soaked the powder in ferric etchant made of (Fe(NO3)3) and HF. This etchant alone made a porous Si precipitant that could be used as the anode material!

 

This all seems very simple, but the researchers describe the process through some basic physics. The etchant acts as a reservoir full of holes (C above) which are attracted to the Fe impurities in the Si, which contain localized electrons (the yellow blob in D, above). These electrons and holes react and the iron leaves, creating a void in the silicon lattice and its resulting porous nature. This is definitely a great place where future research could help identify the best etchant and Si dopants to create porous Si with the highest capacity!

The end result if a battery anode with much better cycling capability. The cycle number above refers to the number of charge/discharge cycles tested using a given anode in batteries the researchers created in-house. In blue, the non-etched anode shows poor cycling, as its capacity along the y-axis decreases significantly with the number of cycles. This demonstrates probably large volume expansion of plain old silicon with charging that leads to pulverisation and destruction of the anode. With the etched anodes using the process described above, the capacity maintains high for large numbers of cycles, especially using the Fe(NO3)3, compard to another type of etchant used, FeCl3. This shows the importance of using the best type of etchant that will react with the impurities in the silicon to create voids in the lattice.

These results should inspire lots of more related studies examining similarly cheap methods to create porous materials for anodes. In particular, it will be important to find an optimal doping level of the silicon that provides the best porous structure with the most surface area for Li sites without creating too fragile a crystal structure.

References

 

Ge, M., Lu, Y., Ercius, P., Rong, J., Fang, X., Mecklenburg, M., & Zhou, C. (2014). Large-Scale Fabrication, 3D Tomography, and Lithium-Ion Battery Application of Porous Silicon Nano Letters, 14 (1), 261-268 DOI: 10.1021/nl403923s

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