Polar firn air reveals large-scale impact of anthropogenic mercury emissions during the 1970s

Abstract

Mercury (Hg) is an extremely toxic pollutant, and its biogeochemical cycle has been perturbed by anthropogenic emissions during recent centuries. In the atmosphere, gaseous elemental mercury (GEM; Hg degrees ) is the predominant form of mercury (up to 95%). Here we report the evolution of atmospheric levels of GEM in mid- to high-northern latitudes inferred from the interstitial air of firn (perennial snowpack) at Summit, Greenland. GEM concentrations increased rapidly after World War II from approximately 1.5 ng m(-3) reaching a maximum of approximately 3 ng m(-3) around 1970 and decreased until stabilizing at approximately 1.7 ng m(-3) around 1995. This reconstruction reproduces real-time measurements available from the Arctic since 1995 and exhibits the same general trend observed in Europe since 1990. Anthropogenic emissions caused a two-fold rise in boreal atmospheric GEM concentrations before the 1970s, which likely contributed to higher deposition of mercury in both industrialized and remotes areas. Once deposited, this toxin becomes available for methylation and, subsequently, the contamination of ecosystems. Implementation of air pollution regulations, however, enabled a large-scale decline in atmospheric mercury levels during the 1980s. The results shown here suggest that potential increases in emissions in the coming decades could have a similar large-scale impact on atmospheric Hg levels.

Fig. 1.

Gaseous elemental mercury (GEM; Hg°) concentrations measured in firn air at Summit Station from 15 to 79.5 m depth. The atmospheric level reported is a mean concentration from three weeks of measurements during both summer 2005 and spring 2006 (21). Above 69 m depth in the firn is the diffusion zone, where gas can diffuse rapidly. From 69 to 80 m is the lock-in zone, where impermeable winter layers prevent vertical diffusion of air, but persistent open porosity allows air pumping. The bars represent one standard deviation confidence interval.

Fig. 2.

Impact of human emissions on the atmospheric mercury reservoir during recent decades. (A) Envelope of modeled concentrations for atmospheric GEM inferred from Summit firn air, central Greenland, during the last 66 years (gray area). (B) Global anthropogenic emissions of mercury to the atmosphere in 1980, 1990, 1995, and 2000 (ref. and references therein) (gray bars) and worldwide production of mercury (black line) (49). Global anthropogenic emissions of mercury presented here are based on emission inventories and include industrial emissions as well as coal combustion. Worldwide production refers to the mercury extracted from geological reservoirs for industrial uses (including mining). Only a fraction of the mercury produced is transferred to the atmosphere by industrial processes.

Fig. 3.

Envelope of GEM atmospheric concentrations inferred from Summit firn air (blue curves), and atmospheric monitoring of GEM available for the Northern Hemisphere at different European and Arctic sites since 1990. Dots and errors bars represent the median and 95% confidence intervals. Data are reproduced from Slemr et al. (8) and Steffen et al. (38).