Stone coal as a potential atmospheric mercury source in Da-Ba-Shan mountain areas, China

Abstract

Mercury (Hg) emissions from stone coal that formed from marine lower organisms in the late Proterozoic and early Paleozoic have not been paid much attention in China. In this research, Hg concentrations in different fueled coals (stone coal, humic coal) and charcoal that derived from wood and paired slags, atmospheric Hg emissions and atmospheric Hg levels were studied in Shaanxi province, China. The average Hg concentration in stone coal produced in Da-Ba-Shan mountain areas in Southern Shaanxi was 539.4 μg·kg−1, about 15 and 38 times higher than that of humic coal (36.0 μg·kg−1) and charcoal (14.2 μg·kg−1), respectively. Atmospheric Hg emission usually lasted for 2–3 h after fueling stone coal, with the majority of Hg emitted during the first 1 h. 95.5–99.4% of Hg in the fuel would be lost into the atmosphere for three types of fuels. Mercury emission factor (MEF) of stone coal was 40–120 times higher than those of humic coal and charcoal based on heat value. Average atmospheric Hg concentration at 0.5 m above the stove could reach 1600–2000 ng·m−3 if burning stone coal, which exceeded the standards for residential ambient air (200–300 ng·m−3) by 5–10 times and also was nearly two orders of magnitude higher than that of burning humic coal (20–60 ng·m−3). Health risk would be a concern for local residents who depend on stone coal for cooking and heating but without any control measures of flue gas. In Shaanxi province alone, Hg emission through domestic combustion of stone coal was estimated to be 1.34 Mg in 2011. Higher mercury emission amounts are possible in southern China where stone coal has been intensively used. Total mercury emissions from this source category need to be further investigated on the national scale.