Tag Archives: atmosphere

Mercury NOMADSS travel to Smyrna, TN!

Greetings from sunny Smyrna, TN, where for the last few weeks we (Noelle Selin, Amanda Giang and Shaojie Song) have been participating in a mission to measure mercury and other pollutants in the atmosphere. NOMADSS is the title of the airplane-based campaign, which stands for “Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks.” It’s part of the larger Southeast Atmosphere study that’s investigating air quality in the southeast U.S. this summer. We are using our models to predict where we’re likely to find pollution, and to interpret data from the last several days to guide planning.

If you’re interested in following all of the science going on this summer, check out the Southeast Atmosphere Study home page, follow @SAS_Operations on twitter. There’s also a great blog on another component of the Southeast Atmosphere Study, the Southern Oxidant and Aerosol Study. Stay tuned for further updates from the field!

For mercury-specific updates, stay tuned to #MITMercury.


Emissions and Releases in the Final Agreement

By: Rebecca Saari and Leah Stokes

Before the negotiations began, we wrote this post summarizing the key issues negotiators were considering for mercury emissions to air and releases to land and water. It was clear that the delegates had much to resolve. What did countries finally decide, and what does it mean? We’ll cover these questions in this post.

Countries addressed how mercury enters the environment by identifying “relevant sources” for emissions in Annex F. The text specifically identifies coal-fired plants and boilers, non-ferrous metal mining activities, waste incineration, and cement production, as sources for mercury emissions that need to be controlled. Oil and gas, facilities where mercury added products are manufactured, and manganese production, which were all included in the draft Annex F at the beginning of the week, were excluded from the final agreement.

Conversely, sources to land and water are not specified in the treaty text. Instead, it is left to Parties to identify these sources within 3 years of the Convention’s entry into force, with the help of the Conference of the Parties. In other words, this decision was left for future rounds of negotiation.

Parties must also create an inventory of their emissions and releases within 5 years the Convention’s entry into force. This is quite a long time. On the one hand, inventories can take a while. Consider that the US Environmental Protection Agency takes three years to issue updates of its National Emissions Inventory of common air contaminants. Still, many countries have been working on inventorying their mercury emissions and releases for many years, in parallel to the negotiations, so, for many countries, a five year period is quite lenient. Many countries have already completed or begun their inventories, and those who haven’t can use the UNEP Toolkit. This inventory is a critical tool for identifying sources and tracking progress. In fact, measuring emissions may be a key way that the treaty changes state behavior over time, by making emissions and releases more visible.

There’s a difference between how the treaty addresses new and existing emission sources. For new sources, parties must apply Best Available Techniques (BAT) and/or Best Environmental Practices (BEP) within five years. To manage existing sources, parties can choose between applying goals, emissions limits, BAT/BEP, multi-pollutant control options, and other measures that reduce emissions. For existing sources, measures must be applied within 10 years for existing sources of air emissions. There isn’t a corresponding deadline for action on releases, though an optional plan of action may be submitted within 4 years.

As discussed above, there are differences in the treatment of emissions to air versus releases to land and water. However, mercury mobilization, whether to the air or water, will have an equivalent fate in the long run, as explained by Helen Amos. Also, our earlier post pointed out that stricter control of air emissions might create perverse incentives to transfer mercury to the water, where it bioaccumulates in seafood and gets into our diets. The relative importance of releases vs. emissions is also an area of ongoing scientific research.

With the adoption of these articles, Parties have made some meaningful progress in policing how mercury enters our environment. The true test of the treaty’s significance and strength will come in the years to follow, as guidance is crafted and implemented. Ultimately, the treaty will need to not only control emissions and releases, but reduce them. In other words, this treaty is just the end of step one.

The Curious Life of a Mercury Atom

by Bethanie Edwards

Hi, a mercury atom here. I’m currently floating in a water bottle of a delegate at the INC5 mercury negotiations in Geneva. As you know, the global community is coming together this week to negotiate ways to prevent my release into the environment. How exactly do I and my fellow mercury atoms make it into the environment to begin with? Let me share my experience with you.

For much of my life I was just a mercury atom sharing electrons with my best friend, a sulfur atom, deep in the earth as cinnabar. My potential toxicity was masked by my rosy appearance. I was expecting to spend my entire life nestled away in the Earth’s crust. But suddenly, I was startled, a loud persistent thud getting closer and closer. It was 1500 AD, and Spanish miners had just dug me out of my lithospheric home in the mountain-sides of Almaden, Spain. That’s when I began my journey, contributing to the 350,000 metric tons of mercury that humans have released into the environment over the last 4000 years.

Illustration from Erker (1574)

Illustration from Erker (1574)

After traveling to a monastery, monks began heating me up. I could feel my bond with sulfur dissipating; I was entering the vapor phase. I was collected in a distillation bulb as I evaporated, separated from the cinnabar. Little did I know, I’d soon be forced into a new partnership (albeit a brief one).

Once condensed into my liquid state and mixed with sluice from gold panning, my affinity for binding with other metals led me to bind together with all of the gold in the river bed sluice, separating the gold from the rock. When the rock was discarded the monks begin heating me up again, ending my short amalgamation with gold. However, this time as I vaporized, I escaped into the atmosphere.

The vapor pressure of mercury is very high, so I floated all the way into the upper troposphere and caught a wind current to the North Pole. Along the way I met a few other mercury atoms. Most of them had found their way into the atmosphere after weathering into rivers and then evaporating, or after being emitted from the eruption of a volcano. I bummed around in the Arctic troposphere for about 6 months.  As I recall, there were quite a few bromine atoms around. I ran into one, lost a few electrons, and then stuck to it. Then we began falling through the atmosphere, luckily there was snow to break our fall. There I waited until summer, when the snow began to melt and I was washed into a fjord.

As the summer progressed in the fjord, phytoplankton bloomed and then died. The bacterial populations began to grow exponentially and, before I knew it, the bacteria had used up all the oxygen. When bacteria deplete all the oxygen gas in an environment, they move on to using other molecules to make a living. Once they started using sulfate (SO42-), my old friend sulfur re-entered the picture. I bound with it and, not too long afterward, one of those bacteria sucked me into her cell. I’m not sure if the bacterium was just interested in the sulfur that I was attached to, or if she found me to be too toxic, but—to my horror—the bacterium quickly tore away the sulfur and stuck me with a methyl group.

Now, I’m not trying to be prejudiced against carbon, but it’s really not a good influence on me. I have enough toxicity problems on my own. And when I’m bound to an organic carbon, I can’t resist diffusing into organisms, be it fish, shellfish, or humans.  That is exactly what happened. After the water that I was residing in was re-oxygenated, a fish came along and I entered its body through the gill tissue, and as I was a methylmercury molecule by then, I wasn’t the only one to do so.

Eventually my fishy friend’s luck ran out; a fisherman caught him and cooked him up for dinner. I stayed inside the fisherman until he lived out his days and was cremated, and I was released back into the atmosphere.

I felt bad for the poor fellow but I was perfectly happy to be back in the atmosphere. I was looking forward to seeing the Arctic again. But to my surprise, I started falling to the Earth very shortly after being emitted. It must have been all the soot that I was associated with. I was deposited on the forest floor. As the seasons turned and leaves fell and decayed, I became buried in the soil. The rains came and went, but I stayed in the forest getting buried millimeter by millimeter deeper into the soil with each passing year. Until the day the fires came, that is.

Sometimes forest fires burn so hot that they scorch the soil. When this occurs, volatile elements like me can be vaporized and released into the atmosphere. While I will admit I was sequestered in the soil for quite a while, I did not expect to see so many other mercury atoms when I returned to the atmosphere. I met mercury atoms that had found their way to the atmosphere after being in fillings in people’s mouths, atoms that used to reside in light bulbs, several atoms that were used recently in gold mining in the depths of the jungle, and of course the atoms that were released from coal.

This time when I met and bound with a bromine radical, I was in the atmosphere over the Swiss Alps. Since Switzerland is a temperate region, it took much longer to get deposited than it had when I was in the Arctic. However, I eventually landed in the waters of the Alps and ultimately made it into the water bottle of an INC5 delegate.

Since I am one of 1.5×1015 mercury molecules in this water bottle alone, I sure do hope that they agree upon and sign a treaty with teeth!


Forms of Mercury: Beyond the Silver Liquid

By: Noelle Selin

It seems a bit strange to hear delegates at an intergovernmental negotiation on mercury discussing how to define “mercury.” Doesn’t the periodic table define it? Not only is mercury an element, but it’s also the reason why we’re all here in Geneva to negotiate an agreement. But defining exactly what is being addressed by the treaty is a critical issue – especially since mercury exists in many different forms in the environment.

Mercury in its liquid form is most  familiar.

Mercury in its liquid form is most familiar.

The chair’s draft treaty text defines mercury as “elemental mercury”. Elemental mercury is the liquid substance that many people recall when they think of mercury. In the atmosphere, most mercury is in elemental form, but it is a gas rather than a liquid. Elemental mercury is often abbreviated as Hg(0).

Another definition in the convention is “mercury compounds,” which addresses forms of mercury other than elemental mercury. What other forms of mercury are there?

Methylmercury is of particular concern, because it is the toxic form of mercury found in fish. Mercury is converted to methylmercury in aquatic systems by sulfate- and iron-reducing bacteria. For more on the health effects of methylmercury, see our earlier post.

In addition to elemental mercury, atmospheric mercury also exists as divalent mercury. Divalent mercury, also referred to as Hg(II), is formed when elemental mercury has undergone a chemical reaction of oxidation, losing electrons. In the atmosphere, Hg(II) can bind with other elements, but scientists don’t yet know exactly what these forms are. The chemical form of Hg(II) in the atmosphere could be HgCl2, HgBr2, Hg(OH)2, or HgO. The leading candidate is HgCl2, [give the name for this?], but this is a topic of current research. When Hg(II) is measured in the atmosphere, it is referred to as reactive gaseous mercury. Forms of mercury found in the ocean include both Hg(0) and Hg(II).

Emissions from different sources release different forms of mercury. Emissions from the surface ocean and land are in the form of elemental mercury. Anthropogenic sources, such as coal power plants, can release both Hg(0) and Hg(II). This is important because the two forms of mercury have different environmental behavior.

Hg(0) lasts for a long time in the atmosphere (6 months to a year), meaning that it circulates around the globe and can travel long distances. Hg(II) can easily rain or settle out after only a few days in the atmosphere, which means it is more likely to enter the environment nearby its source. Thus, reducing Hg(II) emissions will have important local benefits, compared with reducing Hg(0), which has important global benefits.

The behavior of mercury in the environment, however, is complex. Thus, we need to use computer models [pdf] to determine how mercury changes form and travels after it is emitted. These models use the chemical and physical properties of mercury in its various forms to estimate where mercury will travel over time. Mercury deposited to the environment as Hg(II) can return to the atmosphere as Hg(0). Additionally, Hg(0) can react (oxidize) to form Hg(II) in the atmosphere, and Hg(II) can then reduce back to Hg(0). In other words, mercury can change its form. This can occur anywhere in the atmosphere, even when it is being released from power plant plumes [pdf]. Ultimately, all mercury released continues to cycle through the environment for centuries, contributing to the global mercury legacy.

Many of these reactions are not well understood by scientists, so the transport and fate of mercury in the environment is a topic of significant ongoing research.

The Mercury Legacy: Defining “Natural” versus “Anthropogenic” Mercury

by Helen Amos

Written by Helen Amos from Harvard University, this is the first of our Guest Scientist Blogs. Helen is a fourth year PhD candidate in the Earth and Planetary Sciences Department at Harvard. Her research focuses on understanding the biogeochemical cycling and environmental fate of mercury and other toxics. She is currently using state-of-the-science models to get a handle on the impact of past historical releases of anthropogenic mercury on present-day and future levels of mercury in the environment. Email: amos@fas.harvard.edu      Website: http://people.fas.harvard.edu/~amos

When you go out and measure mercury in the environment today, how much of that mercury occurs naturally and how much is the result of anthropogenic (i.e., man-made) releases? This is a critical question with an uncertain answer. Much of the uncertainty stems from not considering the impact of anthropogenic mercury released in the past.

Human activities (e.g., mining) have been releasing mercury to the environment since antiquity (Nriagu, 1994; Cooke et al., 2009; Streets et al., 2011). The result of several millennia of anthropogenic mercury releases is mercury enrichment in the atmosphere, ocean, and soil.

Mercury continuously cycles between the atmosphere, ocean, and soil. Mercury emitted to the atmosphere (e.g., from a coal fired power plant) is eventually deposited to ocean or soil where it may be sequestered or may be re-emitted back to the atmosphere. This creates a “legacy” of mercury in the environment such that much of the mercury today originates from historical anthropogenic releases in the past.

It is all too common that mercury emitted from the ocean and soil is simply referred to as “natural mercury emissions”. However, not all of the mercury currently being emitted from the ocean and soil is truly “natural”. Rather, some fraction is naturally occurring and the remainder is anthropogenic mercury that was once deposited and is now being re-released to the atmosphere.

New work (Amos et al., 2013) suggests that a large fraction of mercury present in the environment today is a legacy of historical anthropogenic mercury emissions. Globally, more than half of the mercury in the ocean today is of anthropogenic origin (Amos et al., 2013). And more than half of the mercury emitted to the atmospheric today is legacy anthropogenic mercury (Amos et al., 2013).

How we define “natural” versus “anthropogenic” mercury has direct relevance to the UNEP mercury treaty. If policymakers want to regulate mercury or set targets for reductions, we need to know what the natural background levels of mercury in the environment actually are. If mercury emissions are incorrectly labeled as natural emissions, the impact of anthropogenic releases is underestimated and our ability to reduce or stabilize mercury concentrations in the environment is overestimated. Decision-makers need to keep this science in mind as they prepare a global mercury policy.



Amos, H. M. et al. (2013), Legacy impacts of all-time anthropogenic emissions on the global             mercury cycle, Glob. Biogeochem. Cycles, in review.

Cooke, C. A., et al. (2009), Over three millennia of mercury pollution in the Peruvian Andes,             Proc. Natl. Acad. Sci. U. S. A., 106(22), 8830-8834.

Nriagu, J. O. (1994), Mercury pollution from the past mining of gold and silver in the Americas,             Sci. Total Environ., 149(3), 167-181.

Streets, D. G., et al. (2011), All-time releases of mercury to the atmosphere from human             activities, Environ. Sci. Technol., 45(24), 10485-10491.

Co-Benefits of Mercury Emissions Reduction

Finding the silver lining in reducing quicksilver

By: Rebecca Saari

As a PhD Candidate researching air pollution, I have enjoyed following the treaty discussions, particularly those focusing on emissions and releases. At MIT, I study the many social and environmental gains from reducing air pollution. Often, targeting reductions of a single pollutant – like mercury – can simultaneously serve to reduce other pollutants as a side-benefit. Finding and quantifying such “co-benefits” is my passion. (My other passions include skiing and chocolate, so it does not hurt that the negotiations are in Switzerland.)

Reducing mercury emissions

Nanticoke, coal-fired thermal generating station in Ontario, Canada, with a total capacity of 3,920 MW, was once the largest coal plant in North America. It will no longer burn coal, by the end of 2013 (Photo by Ontario Power Generation).

If the treaty creates new action to reduce mercury emissions, it can realize gains that go far beyond the direct impacts of mercury alone. Controlling mercury from coal-fired combustion, the second-largest air emissions source, can be achieved with measures that also control other pollutants. In particular, reducing mercury emissions to air can also reduce emissions of particulate matter, sulfur dioxide and nitrogen oxides.

All of these pollutants have significant human health impacts. Estimates of global worldwide deaths due to fine particulate matter exceed 1 million per year. Beijing is currently experiencing extreme levels of fine particulate matter. Countries can use the opportunity presented by this treaty to make progress towards multiple goals in protecting human health and the environment.

Reducing mercury emissions from coal would go a long way towards diminishing the global transport of mercury pollution. Nearly one quarter of all mercury emissions to air arise from the combustion of coal in utility, industrial, and residential boilers.

Many ways to reduce mercury and other pollutants

There are numerous ways to address mercury emissions, which have varying co-benefits.
There are numerous ways to address mercury emissions, which have various co-benefits.

There are many ways to reduce mercury emissions from coal across the entire combustion process, from start to finish, including pre-treating coal, improving process efficiency, and using post-combustion technologies.

Before coal is burned, several actions can reduce mercury, sulfur compounds, and particulate emissions. There are several different types of coal, and they vary in the amount of pollutants they contain. Coal switching and coal blending can allow mercury emissions to be captured more easily. This is a low-tech, potentially low-cost form of mercury reduction. Coal can also be pre-treated through a variety of processes, including washing, beneficiation, and the application of additives. Depending on the type of cleaning and variety of coal, washing alone can remove about 10-80% of the mercury content in coal before combustion takes place.

We can also improve the efficiency of coal plants through operations and maintenance (O&M) measures that lower the emissions intensity of coal-related pollutants including mercury and greenhouse gases, and potentially lead to more sustainable and cost-effective use of fossil fuels. Various O&M measures are effective options. Typically, these approaches target improved combustion efficiency, improved flue-gas ventilation, and reduced leakage and fouling.

Once coal combustion is complete, mercury can be captured using conventional methods designed for other pollutants. Specifically, wet sulfur scrubbers (a.k.a. wet flue gas desulfurization), particulate capture (including fabric filters, electrostatic precipitators), and NOx controls (i.e. selective catalytic reduction) can aid in mercury removal. Depending on the type of coal and configuration of equipment, more than 90% reduction of mercury can be achieved. For additional mercury removal, mercury-specific sorbent injection can be added to the process.

Looking to the future, multi-pollutant control technologies, which aim to reduce key pollutants simultaneously, may gain in popularity. Several systems already exist, at various stages of development, demonstration and commercialization. The mercury treaty has the potential to sow the seeds for broad protection of human health and the environment, beyond the gains due to mercury alone.

Interested in learning more? Three great resources are the UNEP’s “Process Optimization Guidance”, the International Energy Agency Clean Coal Centre and Pacyna et al. There is also an interactive companion to UNEP POG called iPOG, a tool you can use to learn about  options, and estimate your facility’s mercury reduction potential.

Where in the World is Mercury? Part 1: The Atmosphere

by Noelle Selin

Mercury is a slippery little element. One of the reasons that it’s the topic of global discussions is that it’s present everywhere on earth. Mostly, this is a result of human activities, both past and present. Mercury concentrations, though, can be higher in some places than others. Identifying where the problem is, and tracking it through time, will be important scientific tasks as implementation of an eventual treaty moves forward. Here’s a quick summary of what we know about mercury concentrations worldwide, beginning with mercury in the atmosphere.

Mercury in air, which exists primarily as elemental mercury, is present throughout the globe. Since mercury remains in the atmosphere for 6 months to a year after it is emitted, it has plenty of time to circle the globe. Typical concentrations of mercury in surface air are about 1.6 ng/m3, but can be substantially higher near sources. Atmospheric measurements can be used, along with models, to monitor changes in mercury atmospheric loadings and help validate emissions estimates. Much activity in this area has been prompted by the UNEP Mercury Air Transport and Fate Research partnership area (for more on the UNEP mercury partnerships, see our earlier post).

Concentrations of mercury in the air are measured at the ground (at land-based stations and on ocean cruises), on mountaintops, and from airplanes. A key project in this area is the Global Mercury Observation System, which aims to establish a worldwide monitoring system for mercury in air and precipitation. A figure of the distribution of stations is below.

GMOS ground-based monitoring sites

GMOS ground-based monitoring sites

Additional measurements are available from the Canadian Atmospheric Mercury Measurement Network (CAMNet) and the U.S. Atmospheric Mercury Network (AMNet), as well as from individual scientific studies. Measurements of mercury in precipitation are conducted in the US by the National Atmospheric Deposition Program’s Mercury Deposition Network and in Europe by EMEP.

A recent example of mercury measurements from a ship cruise is the global circumnavigation of the Galathea 3 [pdf]. From aircraft, mercury is routinely measured as part of the CARIBIC experiment, in which air pollution monitors are included on Lufthansa commercial planes. In addition, research aircrafts studying pollution also measure mercury. The ARCTAS aircraft campaign in 2007-2008 focusing on Arctic pollution included mercury in its measurements, and in the summer of 2013, the North American Airborne Mercury Experiment (NAAMEX) campaign will fly as part of a larger campaign on the NSF C-130 aircraft (picture below). I will be providing modeling support for the NAAMEX campaign, along with MIT students Amanda Giang and Shaojie Song, in collaboration with the University of Washington.