Methods of Measuring Atmospheric Mercury Pollution

Thought LeadersSeth LymanBingham Center Director and Research ProfessorUtah State University

In this interview conducted at Pittcon 2024 in San Diego, we spoke to Seth Lyman about atmospheric mercury, exploring innovative measurement techniques, and the environmental impact of mercury pollution.

Could you briefly introduce us to your Utah State University role and primary research focus?

I am the director of Utah State University's Bingham Research Center and a research professor in the chemistry department. My research focuses on the atmosphere, including pollution emissions, chemistry, instrument development, and atmospheric fate.

A lot of what I do involves atmospheric mercury. Everyone is familiar with mercury as a silvery liquid. Like other liquids, it has a vapor phase and enters the atmosphere, where it can react chemically before polluting the environment. This is a particular focus of my research.

Why is understanding mercury pollution crucial for both environmental and human health?

Most mercury pollution, or at least when mercury has a toxic impact, occurs in aquatic systems. While we normally worry about mercury pollution in the water, most of it is emitted into the atmosphere. It travels around the globe, undergoing chemical reactions, and this atmospheric travel and chemical reactions determine where mercury ends up and has a toxic impact rather than the pollution source.

Therefore, understanding how much mercury is in the air, its type, its chemical nature, and where it causes chemical reactions can help us determine the origin of mercury in the San Diego Bay area.

Image Credit: H_Ko/Shutterstock.com

What are your main challenges in measuring atmospheric mercury, especially oxidized mercury compounds?

The biggest challenge in measuring atmospheric mercury concentrations is their low levels. We measure it in the low parts per quadrillion range, and our research group particularly focuses on oxidized mercury compounds. They range from about zero to ten parts per quadrillion, which translates to zero to ten molecules of oxidized mercury for every quadrillion molecules of everything else.

There are two more challenges. One is that oxidized mercury compounds are just slightly volatile. They may exist in the gas phase in the atmosphere, but as soon as they come into contact with a surface, they stick to it, even if it is Teflon or something highly inert.

The other challenge is that they tend to be chemically labile. They readily break apart into elemental mercury, so we must find surfaces and handling methods that are both inert and warm to keep these oxidized mercury compounds in the gas phase.

Can you discuss the innovative methods and technologies you are developing to identify and quantify atmospheric mercury compounds?

Elemental mercury is fairly inert and more volatile than oxidized mercury. Many attempts have been made to make a commercial instrument for detecting oxidized mercury compounds in the air.

The one that took off or got some traction turned out to be biased low. Over a dozen articles now show that this method of measuring oxidized mercury is strongly biased low, with the extent of the bias depending on where you are and the chemistry of the atmosphere. Our efforts involve developing alternative methods for this task, and we are working with several partners to do so.

One instrument that we have put together measures oxidized mercury indirectly. You measure total mercury and elemental mercury and then take the difference. This is challenging because total mercury and elemental mercury are much more abundant than oxidized mercury, requiring very precise measurements. We have been able to do this and demonstrate it in a couple of cases.

Another aspect of our work is ensuring that the measurements are correct. We build calibration systems for this task. The abovementioned commercial instrument entered the market. It gained significant attention before it was shown that it did not work well because there was no way to calibrate those measurements.

We have been working to calibrate oxidized mercury for about ten years. We use permeation tube-based methods that are NIST traceable and can deliver very low concentrations of oxidized mercury in ambient air during sampling. We have discovered that mercury measurement systems behave differently in ambient air than in inert gas or scrubbed air.

How are you advancing calibration methods for measuring oxidized mercury, and why is this important?

One way we can do this is by looking at analogs in other fields of chemistry or analysis. For example, semi-volatile organic compounds can give us ideas for dealing with semi-volatile metal-containing compounds.

No other metal behaves like mercury in the atmosphere, certainly not one with the toxic impact and the imperative need to measure it as mercury. We think this might be a viable method for measuring mercury in the atmosphere. To test if it works, we buy some parts and build something. Several companies have been quite helpful as we work to put things together.

One challenge for companies that currently make mercury instrumentation is that, while detecting mercury in the atmosphere is essential, it is not like ozone or CO₂, where there are regulatory pushes that force a government or an agency to buy many of these instruments.

Commercially, convincing a company to build an instrument can be difficult, primarily because the last time, it resulted in complete failure as the instrument was shown not to work properly. So, I do not think we are ready to put these instruments into commercial use just yet.

In your research, how do material selection and temperature control impact the accuracy of mercury measurements?

We need high temperatures to keep these oxidized mercury compounds in the gas phase. We discovered that if they stick to a surface, they never come off as oxidized mercury compounds; instead, they reduce back to elemental mercury, resulting in the loss of our sample.

We use fairly high temperatures of about 150 °C for most of our calibration and analytical instruments. At this temperature, some inert materials start to perform slightly less well. Teflon tends to become more porous at higher temperatures, so we experimented with stainless steel coatings and deactivated fused silica coatings, which perform better.

These oxidized mercury compounds are as inert as Teflon and less porous at higher temperatures, allowing us to increase the temperature while maintaining their inertness.

What could be the next big breakthrough or challenge in atmospheric mercury research, and how do you envision your work addressing it? 

I think many challenges still exist. Perhaps the most discussed topic in the atmospheric mercury community is that the instruments we have developed to measure oxidized mercury in the atmosphere are not compound-specific; they measure total oxidized mercury.

We do not say with certainty what the oxidized mercury compounds in the atmosphere are because there are no methods for measuring them. Because the concentrations are too low, direct measurements with mass spectrometry or similar techniques are impossible, at least for now. Therefore, all the methods are indirect.

We have made attempts at indirect measurement. Using our mercury handling expertise, we do pre-concentration and thermal desorption into a mass spectrometry system. The problem is that the thermal desorption step tends to break down the oxidized mercury compounds.

We are working with a group at the University of Nevada, undertaking extensive research into alternative surfaces that may be more gentle in releasing oxidized mercury compounds into a mass spectrometer.

Even though we have failed so far because we do not have the suitable surface to collect oxidized mercury and then release it intact, we are now getting closer to figuring out how to transmit oxidized mercury onto that surface and then into an analyzer where it could be chemically identified.

As an attendee and now a speaker at Pittcon, what do you find most valuable about this conference? As we mark the 75^th anniversary of Pittcon, could you share your first memory or experience of attending this conference and how it impacted your view of the scientific community?

I was extremely flattered to be invited. Our work is a little niche, but I hope my presentations at Pittcon will spark broader interest in this field and maybe provide opportunities for new collaborations.

Regarding first impressions, I have only been here for one day, but I have already come up with exciting ideas for where to go next. Although my scientific interest is in environmental processes, my approach has been to design instrumentation to help us understand these processes.

Most of the conferences I attend are focused on processes, and it is exciting to talk to people who are more interested in analysis. However, we will not understand the environmental processes if we do not conduct the analysis correctly.

What are you most looking forward to at Pittcon 2024 in San Diego? 

I have signed up for a workshop on measurement uncertainty, which I am looking forward to because knowing how confident you can be in your instrumentation is essential when designing it.

I also look forward to meeting the parts manufacturers and instrument developers we work with. We usually communicate through email, but seeing them face-to-face will be good.

About Seth Lyman

Seth directs Utah State University’s Bingham Research Center, located in Vernal, and is a Research Professor in USU's Department of Chemistry and Biochemistry. He has a doctoral degree in Environmental Science and Health from the University of Nevada, Reno, and his expertise is in atmospheric measurements, instrumentation, and analysis.  Seth's research focuses on the environmental outcomes of energy production.  He and his colleagues at the Center have carried out projects to quantify emissions of organic compounds from various oil and gas sources, understand the conditions that lead to wintertime ozone production in the Rocky Mountain region, and develop computer models of atmospheric emissions and air quality. Seth is also an expert in atmospheric mercury. He has invented several novel methods to measure elemental and oxidized mercury in the atmosphere and calibration systems for those measurements. Seth currently serves on the board of directors for the Utah Clean Air Partnership (UCAIR) and the Utah Legislature's Air Quality Policy Advisory Board.

This information has been sourced, reviewed, and adapted from materials provided by Pittcon.

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