Atmospheric wet deposition of mercury and other trace elements in Pensacola, Florida

W M Landing,K J Gosnell,W C Parker,S D Nolek,J M Caffrey

doi:10.5194/acp-10-4867-2010

Abstract

Abstract. In an effort to understand and quantify the impact of local, regional, and far-distant atmospheric mercury sources to rainfall mercury deposition in the Pensacola, Florida watershed, a program of event-based rainfall sampling was started in late 2004. Modified Aerochem-Metrics wet/dry rainfall samplers were deployed at three sites in the region around the Crist coal-fired power plant and event-based samples were collected continuously for three years. Samples were analyzed for total Hg and a suite of trace elements including Al, As, Ba, Bi, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, La, Li, Mg, Mn, Na, Nb, Ni, P, Pb, Sb, Se, Si, Sn, Sr, Th, U, V, and Zn. Nutrients (ammonia and nitrate) and major anions (chloride and sulfate) were also measured on each sample. Multivariate statistical methods were used to sort these tracers into factors that represent potential source categories contributing to the rainfall chemistry. As, Hg, Sb, Se, Sn, and non sea-salt sulfate were all significantly correlated (R>0.6) with one factor which we interpret as an anthropogenic source term reflecting input from coal combustion throughout the southeastern US. Using ratios of total Hg to volatile elements, we estimate that 22–33% of the rainfall Hg results from coal combustion in the southeastern US with the majority coming from the global background.

Highlights

Atmospheric mercury deposition is a cause for great concern for human health in the United States as well as all other parts of the world due to atmospheric mercury incorporation as methyl mercury into fish
Because of the negative human health effects from Hg exposure, the various states and the US EPA are all working on reducing anthropogenic Hg emissions within the US with the goal of reducing atmospheric Hg deposition
A recent analysis of the global Hg cycle (Selin et al, 2008) suggests that only 20% of the Hg deposition over the USA is due to North American industrial emissions, while 31% is due to sources outside the USA

Summary

Introduction

Atmospheric mercury deposition is a cause for great concern for human health in the United States as well as all other parts of the world due to atmospheric mercury incorporation as methyl mercury into fish. Anthropogenic Hg released to the atmosphere is estimated to be 3.4×109 g/yr (Selin et al, 2008 and references therein). Gaseous elemental mercury (GEM) is believed to have a lifetime of 0.5 to 2 years in the troposphere before it is oxidized and washed out of the atmosphere. The impact of long-range atmospheric transport and deposition of anthropogenic mercury in Greenland was reported nearly 40 years ago by Weiss et al (1971). The increase in the global background of atmospheric mercury due to anthropogenic emissions was reviewed by Fitzgerald et al (1998) and a decade later by Selin (2009). The use of global atmospheric models to evaluate the impacts from long-range transport of anthropogenic mercury is commonplace (e.g. Lin et al, 2010 and references therein)

Methods

Results

Conclusion