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.
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.