Methane Emissions from the Fossil Fuel Industry

The greenhouse effect occurs when atmospheric gases trap heat from the sun’s rays, warming the Earth and the lower atmosphere. The most well-known greenhouse gas, as well as the most abundant, is carbon dioxide (CO2), but non-CO2 greenhouse gases have global warming potential as well. While carbon dioxide accounts for 71.6% of anthropogenic greenhouse gas emissions (1), methane accounts for 20.7%, and N2O accounts for 6.9%. The potential contributions to the greenhouse effect of these gases are quantified in their global warming potential (GWP), usually reported in CO2 equivalents. Methane has a global warming potential of 26-28 CO2 equivalents over 100 years, or 84-87 equivalents over 20 years, due to its shorter lifetime, greater insulating effect, and potential to participate in ozone synthesis in the troposphere (2). Anthropogenic methane sources include industrial agriculture (mostly cattle farming), the fossil fuel industry, other industrial activities. While agriculture contributes the most to anthropogenic methane emissions according to the EPA (1), the fossil fuel industry is an important contributor as well.

An article entitled “Fossil Fuel Industry’s Methane Emissions Far Higher Than Thought” was published in The Guardian on October 5, 2016. The article references the compilation of the largest database of worldwide methane emissions, published in Nature on October 5, 2016 (3). It focused on the result that the methane emissions from the fossil fuel industry (after being adjusted for natural gas methane seepage) are 20-60% larger than previously inventories had suggested. The ‘extra’ methane emissions were compared to those from the Aliso Canyon gas leak (the largest in US history) and shown to be 300 times larger than the emissions from that event. Obviously, the fossil fuel industry’s methane emissions are emitted all over the world and on a much larger timescale than a single gas leak in a single location, so this comparison is not very useful past illustrating sheer volume of emissions.

The lead author of the Nature paper, Stefan Schwietzke, was quoted in the article. Schwietzke emphasized the importance of methane in attenuation of the anthropogenic greenhouse effect and climate forcing in his comments. He went on to say that the models on methane emissions were very sensitive to the data inputs, which is why this new model of worldwide methane emissions is so important. Also quoted was Dr. Grant Allen, from the University of Manchester, in a supposed Nature commentary (which was not linked), stating that climate prediction models need to be reassessed in light of the new data on anthropogenic methane emissions. The article briefly touched on the methodology used in the Nature paper, describing the examination of isotopic ‘fingerprints’ of methane sources over thousands of measurements.

The Nature article, “Upward revision of global fossil fuel methane emissions based on isotope database,” examined worldwide methane emissions by compiling thousands of measurements, and emphasized the increased estimation of methane emissions from the fossil fuel industry (3). It noted that fossil fuel methane emissions are not increasing over time, but are 60-100% larger than previously estimated. After accounting for natural gas methane seepage, the emissions from natural gas, oil, and coal production and their usage are 20-60% larger than estimates. The authors referenced the impact this might have on mitigation of anthropogenic climate forcing due to the fossil fuel industry. The authors used an atmospheric box-model to interpret their database of δ13Csource measurements, choosing their included data to give maximum constraints and therefore greater certainty in their predictions.

The Guardian article includes a figure titled “Emissions from the fossil fuel industry contribute 30 to 45% of atmospheric methane” (shown below), apparently sourced from the Nature paper, but did not include any links. The 60-100% increase over the previously estimated 15-22% range for fossil fuel methane emissions was used to create the figure, but this increase is not adjusted for natural gas methane leakage. The Guardian article references the adjusted range (20-60%) within the first paragraph, so it may be unclear to the reader that the numbers in the figure are from unadjusted estimates. The figure is helpful to demonstrate the fraction of methane emissions that come from the fossil fuel industry, compared to the other sources, but is simplistic and does not accurately portray the findings in the Nature paper.

Overall, I would give the Guardian article an 8 out of 10. It gave good background, quoted scientists involved with the project, and concisely pointed out the implications of their findings. The figure they included was not the best, but communicated more information than it missed due to inaccuracy in either calculation or description. They also did not mention that the fossil fuel industry is a large contributor to CO2 emissions as well, which already informs policy decisions about mitigation of greenhouse gas emissions. In their discussion of how curbing methane emissions would have beneficial effects on climate forcing sooner than CO2 regulations would, they did not mention the largest worldwide contributor to methane emissions, industrial agriculture. Other than that oversight of the (slightly) bigger picture, it was much better than many popular science articles published online.

1. Summary Report: Global Anthropogenic Non-CO2 Greenhouse Gas Emissions: 1990 - 2030 (Rep. No. 430-S-12-002). (2012, December 01). Retrieved October 10, 2016, from https://www3.epa.gov/climatechange/Downloads/EPAactivities/Summary_Global_NonCO2_Projections_Dec2012.pdf 
2. Understanding Global Warming Potentials. (2016, August 09). Retrieved October 10, 2016, from https://www.epa.gov/ghgemissions/understanding-global-warming-potentials 
3. Schwietzke, S., Sherwood, O. A., Bruhwiler, L. M., Miller, J. B., Etiope, G., Dlugokencky, E. J., . . . Tans, P. P. (2016). Upward revision of global fossil fuel methane emissions based on isotope database. Nature, 538(7623), 88-91. doi:10.1038/nature19797 

Shipping and Air Pollution

Recently, a research group based out of Duke University investigated the long term health and climate impact from the maritime industry based in East Asia. A follow up story appeared in EurActiv in collaboration with The Guardian. Across the globe there has been many environmental regulations put in place on ground transportation; however, when it comes to sea transpiration it has often been overlooked. This is likely due to the recent substantial growth of the shipping industry. Indeed, over the past several years the global greenhouse emissions of vehicles have drastically decreased while the emissions from shipping industry has distinctly increased. It is estimated that 3% of the global greenhouse emissions is due to shipping. East Asia has become a significant hotbed of maritime transportation over the past several decades, which is epitomized by the popularity of the “21^st Century Maritime Silk Road” – which stretches from the Chinese coast to Europe through the Indian Ocean. This can be more quantified, however, by realizing that global shipping emissions in East Asia have increased from 4% at the turn of the century, to nearly 16% in 2013. A significant portion of these ships are also foreign. Further, eight out of the ten of the world’s largest ports reside in China. This work spearheaded by Liu, Shindell and He sought to provide a better understanding of the global emissions from shipping in East Asia and to use models to predict the health impacts these emissions had on the coastal regions.

The authors of the study investigated a number of small molecules and particulates including carbon dioxide, sulfur dioxide, NOx and non-methane volatile organics. To carry out this study the research team employed an advanced method which was based on detailed dynamic ship activity data. Impressively, they investigated 78 million hours of vessel operation which they claim is roughly 177 days per vessel. Demonstrated in the first geographic map shown above, the authors point to an increased special distribution of carbon dioxide along the coastal regions and even higher in areas near major ports. They make note that the other small molecules demonstrated similar trends. Moreover, they also demonstrated that nearly 60% of the shipping CO₂ emissions occurred within 20 nautical miles of these coastal regions – mainly from container carriers and bulk carriers. Furthermore, using a methodologly previously published they were able to determine that shipping emissions do indeed have a substantial impact on human health. Not surprisingly, these impacts are largest near the coast. Using this methodology, they determined that there were nearly 24,000 premature deaths in China, Taiwan, Hong Kong, South Korea, and Vietnam.  The research team claim that the particulate matter (PM_2.5) has the most significant deleterious effect on human health.

The writers of the news release articles did a fine job in trying to demonstrate the findings to a general audience. Although the title of the article, “Shipping air pollution cause 24,000 deaths a year in East Asia,” is accurate some can also view it as a bit over the top. One point of contention that I would point out with the follow up story is that they claim that sulfur dioxide is the main culprit leading to adverse health effects – such as cancer. However, in the study itself they state that it is particulate matter that is of most concern. In a general sense I would rate it high (8/10) because the story, although certainly abridged, can help bring to the public eye that the perpetuators of climate change are constantly changing. Twenty years ago it was vehicles – today its ships!

Press release

https://www.euractiv.com/section/transport/news/study-shipping-air-pollution-causes-24000-deaths-a-year-in-east-asia/

Nature - Climate Change, article

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3083.html

Magnetite Nanoparticle Pollution May Be Linked to Alzheimer’s Disease

            Magnetite  (Fe²⁺/Fe³⁺), a dark gray, metallic mineral, most well known for its strongly magnetic properties, is mined for a variety of industrial and commercial uses. The magnetite oxide Fe₃O₄ is a common oxide of iron, and is predominantly found in sedimentary rock⁴.  Because of iron’s role in biological processes, magnetite is known to be naturally occurring in human tissues and a number of animals.  Notably, it is associated with the cellular response that allows use of magnets for medical imaging, such as with Magnetic Resonance Imaging (MRI)^2,3.  Magnetite in biological tissue exists in the form of nanoparticles, particles ranging from 1-100 nanometers in size⁶. Additionally though, nanoparticles or nanospheres of magnetite can also be formed by high-temperature combustion or friction, common in fuel processing and usage. The resulting particulate matter (PM) ultimately contributes to a large portion of the world air polution². When exposed to an external magnetic field, magnetite nanoparticles lead to production of radical oxygen species, and in the case of the biogenic particles (by way of ß-amyloid), can lead to brain tissue damage in the form of amyloid plaques^2,5,7. Recent research reveals the toxicity of magnetite nanoparticles, and links them to neurodegenerative diseases, such as Alzheimer’s Disease (AD), in which oxidative tissue damage and “senile plaque” formation are standard^2,5. While a study³ in 1992 by geophysicist Joe Kirschvink and coworkers, confirmed the presence of natural magnetite in the human brain and its ability to oxidatively damage tissue, it was not until recently, as reported by Maher et al. at Lancatser University, that externally formed magnetite particles can enter the human body, and lead to similar biological harm².

Due to the health hazard of the particulate magnetite, and its increasing presence as a pollutant in urban areas, Maher and her research team used a variety of analytical techniques such as high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and energy dispersive X-ray (EDX), to study the characteristics and levels of magnetite nanoparticles in human brain tissue.  Specifically, postmortem brains of individuals who had lived in the highly polluted, urban areas of Mexico City and Manchester, UK were examined. This research², published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), identified magnetite PM in the brain samples, and analyzed the samples through crystallographic measurements and imaging techniques to further understand the particulate properties. While high levels were seen across ages and residential areas, the highest quantity was found in a 32-year-old individual from Mexico City. Most of the magnetite nanospheres found in the frontal cortex tissue were distinguished as round and spherical in shape, and were often associated with other transition metals such as Pt, Ni, Co and Cu. These morphological features differed greatly from natural magnetite crystals, which are smaller, more “angular, cubo-octahedral,” and are not typically found in the presence of additional metals². Maher et al. concluded that these large, spherical magnetite particles result from external sources, as the geometry, size, and association with other metals, closely resemble particulate matter (PM) formed by high-heat manufacturing and vehicle processes. The authors believe that due to the small magnetite PM mass and diameter, as compared to other common airborne nanoparticles, they may be overlooked by governmental regulation. However, the high concentration of magnetite particles, and their contribution to urban air pollution is concerning due to the uniquely, relatively easy entry into the brain, and should be a public concern. While the PNAS study found highest PM concentration in brains from older individuals (>65 y at death), particularly those with Alzheimer’s disease, there were also markedly high PM concentrations in brains of people younger than 40-years-old at death. Finally, the authors discussed that the externally acquired magnetite PM may be correlated to increased “risk” of AD (using previous studies and controls to support their claims), but were careful to note the need for much further study to make any decisive conclusions². 

Justin Worland’s article in TIME, “Toxic Air Pollution Can Penetrate the Brain: Study”¹ attempts to summarize the findings in the PNAS publication and links it to multiple previous studies about pollution. Worland cites Maher’s work as he describes the negative impacts of pollutants on human health, specifically the new evidence that particles in the atmosphere can lead to harmful effects on the brain. The article correctly informs the reader that magnetite particles, a common urban pollutant, can enter humans through the olfactory nerve (if <200 nm), and ultimately reach the brain tissue.  Worland goes on to describe air pollution as a “top global health threat,” which is leading to premature deaths worldwide¹. He highlights China and India, with their infamously high air pollution levels, but also points out the alarmingly high number of deaths in the “comparatively clean” U.S. and UK, due to anthropogenic air pollution¹. Readdressing Maher’s research, Worland explains the characteristics of the recently analyzed magnetite particles found in the human brain tissue, noting their difference from the naturally occurring nanoparticles. Finally, the TIME article states that the PNAS publication details a potential means by which urban pollution may cause Alzheimer’s, but Worland, like Maher et. al, is careful to note the need for further research.

In general, Justin Worland’s TIME article does a sufficient job presenting important findings of the PNAS publication.  Worland clearly states how the magnetite nanoparticles enter the brain, and explains that the high levels of magnetite result from airborne pollution, evidenced by the unnatural shape and composition of the specific particles examined.  Moreover, he does this in a clear and understandable way, given the complicated nature of the research. While helpful, however, the article has some shortcomings. . The author’s decision to gloss over what magnetite is and how it is formed is an immediately apparent deficiency. While he states that this particle can be  a pollutant, the fact that magnetite is a naturally occurring mineral in both humans and the earth’s surface is completely ignored, leaving one to conclude that by addressing the human creation of the pollutant, the problem could be reduced or eliminated. The TIME article also poorly explains the conclusions drawn from the Maher study by exaggerating  the findings and failing to address the true motivations behind the work. The article’s title, “Toxic Air Pollution Can Penetrate the Brain: Study,” is immediately followed by the broad statement, “air pollution contributes to millions of premature deaths each year,” inadvertently linking the magnetite particles that can enter humans through the olfactory nerve, to previous and unrelated studies about air pollution and premature deaths. He glosses over the fact that it is biological redox processes that may spur degenerative diseases in brain tissue, simply stating that general particulate pollution exposure could cause AD. While the PNAS publication does address premature death due to Alzheimer’s disease, and addresses the possible link between AD and high levels of magnetite in the brain, it was intended to prove that the presence of many frontal cortex magnetite nanoparticles have external origin, rather than biological. Maher explored the correlation between these pollutants and neurodegenerative damage, but states that their “preliminary” results “warrant more intensive study” on this topic². While the TIME article does address this at the end, the title and bold first sentence unavoidably link the two statements in the reader’s mind. An additional shortcoming of the TIME article is the linking to other popular media articles, many of them also in TIME, which Worland uses to support the facts provided.  Many of these other sources use data found before the PNAS research, and are somewhat unrelated. Interestingly, the article cited by Worland when discussing the smog issues in China actually details an air quality improvement in Beijing.

Overall, while I believe that the TIME article accurately portrays the significant findings from the peer-reviewed PNAS article in an understandable fashion, Worland adds additional information and words his statements in way that might misinform the reader. The PNAS article aimed to identify and characterize the non-biological source of magnetite in human brain tissue by analytical techniques, while Worland utilizes the publication to overemphasize the preliminary link between premature death and pollution, and generalizes the findings on magnetite PM to pollution overall. With this in mind, I would give Worland’s article a 6 out of 10.

1) Worland, Justin. "Toxic Air Pollution Can Penetrate the Brain: Study." TIME, September 6, 2016 http://time.com/4480016/air-pollution-health-effects/.

2) Maher, Barbara A. "Magnetite pollution nanoparticles in the human brain." Proceedings of the National Academy of Sciences of the United States of America, (September 2016). http://www.pnas.org/content/early/2016/08/31/1605941113.full.pdf.

3) Kirschvink, Joseph L., Atsuko Kobayashi-Kirschvink, and Barbara J. Woodford. "Magnetite biomineralization in the human brain." Proceedings of the National Academy of Sciences of the United States of America 89 (August 1992): 7683-87.

4) Wikipedia. "Magnetite." 2016. https://en.wikipedia.org/wiki/Magnetite.

5) Price, Michael. "Industrial air pollution leaves magnetic waste in the brain." Science, September 2016. DOI: 10.1126/science.aah7262.

6) Mandal, Ananya. "What are Nanoparticles?." News-Medical.net. 2016. http://www.news-medical.net/life-sciences/What-are-Nanoparticles.aspx.

7) Wikipedia. "Amyloid beta." 2016. https://en.wikipedia.org/wiki/Amyloid_beta.

Linking Long-Term Air Pollution Exposure to Insulin Levels

            Diabetes is a chronic metabolic disease that affects 8.3% of people worldwide.¹ The three types of diabetes are type I (also called juvenile diabetes), type II, and gestational diabetes.² Type II diabetes accounts for approximately 90% of all diabetes cases worldwide and develops gradually following long periods of insulin resistance, which is considered an independent predictor of diabetes.¹ Obesity, specific gene variations, poor nutrition, and lack of exercise have all been identified as risk factors for type II diabetes.¹ In the past five years, air pollution has also been proposed to be an additional risk factor for type II diabetes. This has motivated several research groups to investigate this topic.

            In their recent publication in Diabetes, Wolf et al. detail their study of the relationship between long-term exposure to air pollution and biomarkers related to air pollution.¹ They collected data from a group of 2,944 participants that contained non-diabetic, pre-diabetic, and diabetic individuals. They analyzed HOMA-IR (homeostatic model assessment for insulin resistance), glucose, insulin, HBA_1c (haemoglobin A_1c, identifies average plasma glucose), leptin, and hs-CRP (high-sensitivity C-reactive protein) in relation to long-term exposures to particulate matter ≤ 10 μm in diameter (PM₁₀), between 2.5-10 μm (PM_coarse), and ≤ 2.5 μm (PM_2.5) as well as nitrogen oxides. They discovered that exposure to NO₂ showed significant positive association with HOMA-IR, glucose, insulin, and leptin levels for participants from all subgroups. Furthermore, PM₁₀, PM_coarse, PM_2.5 absorbance and NO_x showed positive associations with HOMA-IR and insulin levels. These results led the authors to conclude that there is a positive relationship between traffic-related air pollution and biomarkers related to insulin resistance. As one would expect from a scientific publication, Wolf et al. as conservative with the wording of their conclusions and are careful not to overstate the meaning of their findings.

            John Raphael of Nature World News summarized the findings of the report by Wolf et al. in his article, “Warning! Air Pollution Could Lead to Diabetes.”³ The title of Raphael’s report suggests that he is much less conservative than Wolf et al. when associating air pollution with diabetes prevalence. However, Raphael is fairly careful in the body of his article to accurately communicate the results of the study without inflating the conclusions made by Wolf et al. Furthermore, Raphael provides a reasonable amount of relevant information about the study without overwhelming the reader with technical jargon. Despite this, I do think Raphael could have been more careful in the first statement of his report, where he claims that, “exposure to air pollution could lead to diabetes.” Wolf et al. linked long-term exposure to air pollutants with increased insulin levels, which can lead to diabetes. This caveat is important, and I think Raphael should have been more careful about how he began his article. Despite this, I found Raphael’s report to be a great bridge between the science that was reported on and a more general audience.

            In conclusion, I thought Raphael skillfully communicated the most important results from Wolf et al.’s extensive study on the relationship between long-term air pollution exposure and insulin levels. While the title of Raphael’s article made it seems as though he might overstate the conclusions made by Wolf et al, I thought he did a fairly good job of translating the scientific article into a digestible and informative report. As such, I would give his article a score of 9/10.

1.     Wolf et al. “Association between long-term exposure to air pollution and biomarkers related to insulin resistance, subclinical inflammation and adipokines.” Diabetes 2016 http://dx.doi.org/10.2337/db15-1567.

2.     Wild et al. “Global prevalence of diabetes.” Diabetes Care 2004, 27, 1047.

3.     John Raphael “Warning! Air pollution could lead to diabetes.” Nature World News. http://www.natureworldnews.com/articles/28506/20160912/warning-air-pollution-could-lead-to-diabetes.htm

Haze from Indonesian Forest Fires

Indonesian farmers utilize fire to clear land cheaply and quickly for oil palm and timber plantations.  The terrain consumed by fire is known as peatlands, which consist of highly combustible organic matter.  Peatlands release large quantities of fine particulate matter (PM_2.5), which is the leading cause of global pollution-related mortality.¹  El Niño and positive Indian Ocean Dipole (pIOD) conditions cause peatlands to become extremely dry and susceptible to large fires that produce large amounts of PM_2.5 enriched smoke/haze.¹  The effect of this haze was first observed in 1997 and twice since then in 2006 and 2015.  All three events caused billions of dollars in damage and thousands of premature deaths.²

The thegardian article³ discusses how Indonesian and near by countries reject a scientific study that claims deliberately set forest fires caused over 100,000 premature deaths in 2015.  The news article rightfully takes and unbiased approach to the discussion on this subject, revealing both parties views and opinions.  I believe this article was written extremely well and leaves the reader to decide which side they will take on the subject.  A downfall of the news article is that it does not directly link to the scientific publication it refers to.  I actually found the publication through a New York Times article, written about the same subject.  The article states that models in the scientific publication rely on assumptions, but the article does not provide examples of the assumptions being made, which I believe would add to the significance of the news article.

The scientific paper, published in Environmental Research Letters, introduces a model framework that can provide areas with information to reduce and/or avoid forest fires that diminish human health in regional areas.  The first thing I noticed about this paper was that a lot of acronyms were used, which are not a bad thing unless it is not stated what the acronym stands for.  I found this to be the case in some instances of the publication.  The authors do explicitly discuss the limitations of their model in the discussion section, which is important because it shows the authors thoroughly thought out their research.  However, a downfall to this could be the scientific validity of the estimations determined by the model.

Overall I thought the news article did a good job of summarizing the journal article’s main points. Other news article I read on this subject focused heavily on the death numbers and who is to blame.  I liked how this news article was shaped in a debate style because I believe it is appropriate for the subject.  The news article definitely has more political views and opinions then what I am used to reading in peer-reviewed articles.  The news article does agree in regards to the factual information published by the publication.  I would give the thegardian article an 8.5/10 score.  It is easy to understand and concise.

1.  S. N. Koplitz et al. Environ. Res. Lett. 2016, 11,094023.

2.  M. E. Marlier et al. nat. Clim. Change 2013, 3, 131-6.
3.  “Indonesia dismisses study showing forest fire haze killed more than 100,00 people” thegardian.com: Sept. 21, 2016 [thegardianarticle]

Four New Ozone Depleting Substances Detected in the Atmosphere

Ozone-depleting substances (ODSs) are synthetic chemicals partially responsible for the degradation of the protective layer of ozone in the stratosphere.¹ As this layer of ozone is instrumental for blocking harmful UV rays emitted from the sun, its depletion due to anthropogenic sources has been a primary environmental concern since the discovery of this problem in the late 1970s.  The synthetic chemicals responsible for ozone depletion (chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, etc.) notably contain carbon-halogen bonds that can undergo photodissociation to extrude atomic halogens, which subsequently catalyze the decomposition of ozone into elemental oxygen.² Thus, the Montreal Protocol on Substances that Deplete the Ozone Layer (MP) was enacted in 1987 through the Vienna Convention for the Protection of the Ozone Layer. The MP has led to the drastic decrease in the emissions of chemicals that cause ozone depletion.¹

In his NBC new article,³ Alister Doyle reports on the discovery of four new industrially-produced gases that are linked to ozone depletion. In his effort to summarize the results originally reported in Nature Geoscience, Doyle neglects to name exactly which new gases (CFCl₂CFCl₂, CF₂ClCCl₃, CF₃CCl₃, CF₃CH₂Cl) have been detected. This is arguably an important detail of the report that has been excluded presumably due to the general audience being targeted through this media source. Despite this lack of specific information, Doyle does provide a reasonable explanation of how the new gases were detected in ice cores harvested in Greenland and Tasmanian air samples. Doyle is also clear that the scientists reporting these data are unsure of how these new emissions are being produced and that these new emissions exist in low enough concentrations in the atmosphere that they are not yet detrimental to the ozone layer. 

J. C. Laube et al. disclose in Nature Geoscience the detection of three new chlorofluorocarbons, (CFCs = CFCl₂CFCl₂ [a], CF₂ClCCl₃ [b], CF₃CCl₃ [c]) and one new hydrofluorocarbon (HCFC = CF₃CH₂Cl [d]).⁴ Laube and co-workers were able to detect these new gases by analyzing air samples collected in Cape Grim, Tasmania (Southern Hemisphere) from 1978 to 2012 as well as deep firn snow samples collected in Greenland (Northern Hemisphere) in 2008. I enjoyed reading about the comparison of these two data collection methods, and was intrigued about  how the levels of the CFCs and the HCFCs varied from one site to another. Interestingly, these four new gases were documented in higher concentrations in the Greenland location than the Tasmania location. The authors claim this is a result of there being more industrialized countries in the northern hemisphere as opposed to the southern hemisphere. Furthermore, they claim that this result suggests entirely anthropogenic sources of these compounds as they are not detectable in air before 1960. Interestingly, compound c has grown in abundance from the 1960s, when it was first detected, to 2012. This is particularly intriguing as its behavior is the opposite of that of its isomer, CF₂ClCFCl_2, which has been decreasing in concentration for decades. The authors nicely highlight the importance of atmospheric lifetime for these CFCs and HCFCs as atmospheric lifetimes are necessary in estimating the beginning of their global emissions. The authors then discuss the stratospheric measurement of the ozone depletion potential, which represents the global ozone loss due to the release of a particular molecule relative to a reference CFC. Importantly, with these measurements they find that the new CFCs are comparatively dangerous to the ozone layer, although they are not yet present in large enough concentrations to begin having measurable detrimental effects. Interestingly, with the lifetime estimation of these CFCs in combination with a two-dimensional chemical transport model, the authors were able to infer global emission of each of the newly reported chemical compound. Currently, it is unknown where these new CFCs and HCFCs are being produced because of caveats with the Montreal Protocol in addition to officially-granted uses of previously-banned CFCs. Specifically, there are no clear regulations on some intermediates generated during the production of certain chlorofluorocarbons, which could lead to the detection of these new gases. The article concludes by highlighting the limitations of the Montreal Protocol and current research focused on determining the source of these new emissions.

While Alister Doyle does fail to identify the four substances that have been measured in the atmosphere, I don't think this is a significant drawback. This is an NBC News article and as such I don't think the general readership is geared toward those with advanced science degrees. With that said, an active link to the original Nature Geoscience article is included in this short publication, which is greatly appreciated.  Overall, I would rate Alister's article as a 7.5/10. I was able to gather all of the general information out of the NBC News article I needed. Further, I feel the many direct quotes from J. C. Laube validate the scientific merit of this popular media article. However, Doyle begins the article by seeming to make the claim that the Montreal Protocol of 1987 is comprehensive and  clear bans are in place for all CFCs and HCFCs. This is a clear overstatement as rightfully pointed out by Laube toward the end of the Nature Geoscience article where it is stated that there are "many caveats in the Montreal Protocol"  as well as "it might be worth reconsidering its reporting regime, including the differentiation of isomeric forms." I feel that certain phrases such as "industrial gases" could be left out by Doyle, as phrases like this tend to carry negative connotations.  Until we know exactly where these gases are coming from we maybe shouldn't be generalizing these gases as purely "industrial."

1. R. W. Portmann et al. Science 2009, 326, 123.

2. E. Wolff et al. Atmos. Chem. Phys. 2007, 7, 4375.

3. A. Doyle,"Four New Ozone-Killing Gases Detected: Scientists Look for Source," NBCNews.com: March 9, 2014. [NBCNews Article]

4. J.C. Laube et al. Nat. Geo. 2014, 7, 266.
Nat Geo