Report examines global mercury sinks that contribute to air pollution and further illustrates a need to standardize measurement techniques
RENO – Gaseous elemental mercury (Hg0) is a semi-volatile chemical, and the only metal that easily exchanges between land surfaces and the atmosphere. Despite nearly 40 years of scientific research, major uncertainties still exist concerning the environmental factors controlling these exchanges and their impacts on atmospheric mercury pollution loads.
A new study published in Environmental Science & Technology has, for the first time, compiled more than 200,000 individual mercury flux measurements measured at 243 different sites mainly across North America, Asia, and Europe.
Analyzing data and results from 132 scientific studies dating back more than 35 years, a research team at Nevada’s Desert Research Institute has statistically examined the magnitude of mercury fluxes, the environmental factors that control them including solar radiation, air and soil temperatures, soil moisture, and soil and atmospheric mercury concentrations, and provided new constraints on these fluxes worldwide.
“Our worldwide scaling of mercury fluxes has revealed several patterns previously unseen,” explained Yannick Agnan, lead author on the report and a postdoctoral fellow of biogeochemistry at DRI. “Most significantly, we estimate global emissions from land surfaces at 607 metric tons annually, which is a significant amount of the total atmospheric emissions. However, the database illustrates that large areas of the globe are nearly fully void of any mercury flux data, including Africa, Central Asia, Australia, and many polar regions.”
The report also showed lower mercury emissions from mining and geothermal sites than previously anticipated. However, emissions from what were once considered background areas in East Asia, with a high atmospheric mercury pollution load, are unexpectedly high. According to the authors, these areas contribute approximately 45-percent of the current land-based global terrestrial mercury emissions. The largest uncertainties in landscape mercury fluxes stems from vegetated areas such as forests and grasslands which likely constitute an important atmospheric mercury sink, but current data is highly uncertain.
“Mercury is a neurotoxic element found naturally in the environment and in the atmosphere, but human activities such as fossil fuel combustion, mining, smelting and waste combustion have increased global atmospheric mercury pollution by a factor of three to five over the last 150 years,” explained Daniel Obrist, Ph.D., one of the reports co-authors and research professor who leads DRI’s Environmental Mercury Laboratory in Reno, Nevada. “While we have a fairly good knowledge of current anthropogenic mercury emissions, our understanding of the role of natural ecosystems is very limited so we don’t well understand which systems serve as net sinks and net sources globally.”
The database also compared two of the most common measurement techniques for measuring mercury fluxes from terrestrial environments. The first, dynamic flux chambers (DFC) are used for the majority of measurements (approximately 85-percent) and compare inlet and outlet mercury concentrations in a chamber placed over a specific area. The second type, micrometerorological (MM) approaches, are based on measurements of vertical concentration gradients above the surface coupled with characterizations of atmospheric turbulence.
“Although MM measurements best represent natural conditions in the field, they are uncommon and often hard to execute,” explained Chris Moore, Ph.D., a co-author and Senior Scientist at the Gas Technology Institute, formerly an assistant research professor at DRI. “DFCs, on the other hand, can directly influence the local area being measured. Thus, we strongly recommend standardization of all flux measurement methods, design and operating procedures that are currently not in place.”
For more information about DRI's mercury research please visit - http://www.dri.edu/mercury-analytical-lab/lab-description