Examining the Relationship Between Power Plant Emissions of Mercury and Ambient Mercury Measurements

Christopher M. Rogers, H. Kemp Howell, Kevin P. Mishoe, MACTEC Engineering and Consulting, Inc., Thomas F. Lavery, Kleinfelder, Inc.

ABSTRACT:

Power plant emissions of sulfur and nitrogen oxides produce pollutant gases and form fine particles in the atmosphere that impair visibility and contribute to acid deposition, which leads to a wide range of environmental impacts. Title IV of the 1990 Clean Air Act Amendments (CAAA) required significant reductions of sulfur dioxide and nitrogen oxide emissions. By 2006, electric power generating sources had reduced their emissions of sulfur dioxide by 46% from their 1995 levels and also reduced NOx emissions by 49%. Declines in wet and dry sulfur deposition have been reported between 1990 and 2007 using data from the Clean Air Status and Trends Network (CASTNET), which measures ambient levels of sulfur and nitrogen compounds. Decreases in nitrogen deposition have also been reported between 1999 and 2007. Power plants also emit measurable quantities of mercury. These emissions contribute to mercury deposition, which leads to contamination of sensitive ecosystems. Mercury can accumulate in the environment and is toxic to humans as well as other life forms. In 2005 the EPA promulgated the Clean Air Mercury Rule (CAMR) to control mercury emissions. However, CAMR was vacated by the D.C. Circuit Court in February 2008. Consequently, EPA is reconsidering its approach to Hg emissions control. Data on mercury emissions exist for some power plants and a national ambient monitoring network for measuring concentrations of mercury in precipitation has been operating since the mid-1990s. The objective of this work assignment is to examine the relationship between sulfur and mercury emissions from fossil fuel power plants and ambient monitoring data for sulfur and mercury species to determine if a secondary benefit in mercury reductions has been achieved from the 1990 CAAA.

 

INTRODUCTION

Mercury is a highly toxic element that is found both naturally and as a pollutant released to the environment. Burning coal in combustion processes, alkali and metal processing, medical and other waste, and mining gold and mercury contribute to mercury concentrations in the environment. These sources emit mercury to the atmosphere where it is widely dispersed. Mercury in the atmosphere is not readily scavenged and can circulate for years. Consequently, atmospheric deposition is the dominant source of mercury over most of the earth. Natural sources of atmospheric mercury include volcanoes, geologic deposits of mercury, and volatilization from the ocean.

 

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