Applicability of USGS Databases for Estimating Global Mercury Input from Coal Use

Estimates of mercury input to coal combustion systems are sought in international efforts to understand and limit the impact of mercury. Here we consider the applicability of a new USGS database, the World Coal Quality Inventory (Tewalt et al., USGS Open-File, 2008), and existing data for U.S. coals (Bragg et al. Open-File 97-134), to estimate mercury input among the world's three largest coal producers, China (~2,550 Mt), the USA (1055 Mt), and India (~430 Mt; World Energy Council, U.S. Energy Information Agency 2006 estimates). Together, these countries account for more than 60% of world coal production, with output in China increasing at more than twice the world rate of increase.

For China, the USGS database includes 305 samples of coal produced for power generation and industrial purposes, collected from active mines throughout the country. These samples give a mean of 0.15 ppm, slightly less than a compilation of 1,699 samples by Zheng et al. (0.19 ppm; STOTEN, v. 384, p. 374, 2007) containing a greater proportion of mercury enriched Guizhou Province coal. These limited data for Chinese coal give a mean roughly comparable to the more comprehensive U.S. in-ground mean (0.17 ppm) for over 7,000 samples. The 1999 EPA Information Collection Request remains the best estimate of mercury input to U.S. utility boilers (0.10 ppm), lower than the in-ground mean due to coal preparation and selection of a greater proportion of low mercury western coals than in the database. Mercury inputs of 380 to 485 t for China and a maximum of 180 t for the U.S. are estimated from production and in-ground means given above. For India, 102 USGS samples include coals in the Sohagpur Basin and reconnaissance sampling of Tertiary coals, together giving a mean of 0.09 ppm mercury, but with insufficient coverage to estimate an India-wide mean.