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.

5 thoughts on “Co-Benefits of Mercury Emissions Reduction

  1. Vivek Sakhrani

    Thank you for the quick overview of why reducing mercury emissions is important and the various control methods. Can you please tell us more about the techniques that delegates / nations prefer and why?


  2. William Clark

    Damage function for mercury…

    Both the news reports on the negotiations, and this blog series, seem strangely mute on the subject of why we care about mercury emissions.

    What is the current consensus about damages mercury emissions cause to humans? To nature? To the built environment? Are these damages focused on particular places or generations?

    How big are these damages relative to other emission products? In particular, with reference to this ‘co-benefits’ discussion, for which policy actions are reduction of mercury-caused damages a big part of the total benefit package, and for which are they a relatively minor part?

    Maybe I’ve missed it, but the discussion seems so focused on emissions and costs and treaty options that the reason for worry seems lost….

    1. Noelle Selin

      Thanks for your thoughtful blog comments! We have a few new posts on health impacts: .
      There was a recent article in Environmental Health () that estimated annual damages in the EU from mercury at 8-9 billion euro per year.
      Along with your Harvard colleague Elsie Sunderland, I wrote a commentary on that article: see
      Amanda Giang and Rebecca Saari are both grad students working with me who are focusing their research on quantifying health impacts of pollution (mercury and ozone/PM, respectively), and I’ve asked them to comment here too.

  3. Amanda Giang

    Great point! Hopefully we address this gap a little in this posts on health effects:

    These are great questions about the scale of mercury’s damages, particularly compared to other pollutants. I think part of the challenge of answering this questions has to do with the diversity of assumptions and methods researchers are using to quantify benefits. Estimates for US and EU damages are around 8 bill./yr*. My own research actually concerns how we assess the damages of a multi-scale, multi-temporal pollutant like mercury, particularly when some health effects are still uncertain. I’ve just done a quick post on the potential cardiovascular effects of mercury, and what this might mean for policy benefits:

    Would love to get your thoughts!

    *from: Rice et al. (2010) A probabilistic characterization of the health benefits of reducing methyl mercury intake in the United States.
    Trasande et al. (2005) Applying cost analyses to drive policy that protects children: mercury as a case study.
    Bellanger et al. (2013) Economic benefits of methylmercury exposure control in Europe: Monetary value of neurotoxicity prevention.

  4. Rebecca Saari Post author

    Hi Prof. Clark,

    Thank you for your interest and your comment. These issues – quantifying and understanding co-benefits – are complex, and at the heart of some our ongoing

    I’ll try to provide some context for your questions specific to co-benefits.

    First, it helps to learn a bit more about how mercury differs from pollutants like particulate matter, nitrogen dioxides, sulfur dioxide, and ozone. First,
    in terms of abundance, global emissions of these common contaminants are much higher than those of mercury (e.g., emissions of particulate matter (<10
    um from the US alone are over three orders of magnitude higher than global mercury emissions). Next, in terms of damages, mercury’s main impacts are to IQ
    (Amanda is working on cardio impacts), while other pollutants have various health impacts including premature death. The exposure route also differs:
    mercury damages are due mainly to fish consumption, and due to inhalation of ambient air for the other pollutants. Given these difference in abundance,
    exposure, and types of damage, let’s consider the relative impacts.

    “How big are these damages relative to other emission products?”

    While we don’t have comprehensive global information, current studies of Europe, the US, and China suggest that damages from mercury are several orders of
    magnitude lower than those from the common air contaminants. Take the example of Europe. Prof. Selin and Amanda cited studies estimating damages from
    mercury at 8-9 billion euro per year. Our group has estimated damages from particulate matter (<10 um) and ozone at 217 billion euro per year in 2005 euros. Better quantifying the uncertainty
    in these estimations is also part of our ongoing work, both for mercury and for common contaminants.

    For the recent US MATS, the co-benefits due to particulate matter exceed those for
    mercury. Of course, that assessment only quantified the IQ-related impacts of mercury.

    “In particular, with reference to this ‘co-benefits’ discussion, for which policy actions are reduction of mercury-caused damages a big part of the
    total benefit package, and for which are they a relatively minor part?”

    This is a complex issue, one we are hoping to address in future research. The relative magnitude of benefits would depend on the particular configuration
    of the mercury control strategy employed by a plant, and the main objective of any co-pollution strategy. It is challenging to make a general statement
    about the relative benefits for a given policy action. That said, I hope the classification in the attached table is useful.


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