Fluoride and sulfur dioxide indoor pollution situation and control in coal-burning endemic area in Zhaotong, Yunnan, China

The presented study aims to investigate the gaseous fluoride and sulfur dioxide (SO2) pollution level in the kitchen, traditional flue-curing barn and outdoor environment and to find economically feasible method to reduce fluorine and sulfur release. The gaseous fluoride and SO2 concentrations in air of outdoor environment, kitchen and traditional flue-curing barn were determined in 56 households in coal-burning endemic fluorosis areas of Zhaotong. Among these, 21 households in Yujiawan Village, Zhenxiong County, Zhaotong City were chosen for this experiment to reduce gaseous fluoride and SO2 concentration in traditional flue-curing barn air by using calcined dolomitic siliceous limestone (CDSL) instead of clay mixed with coal. The result showed that: (1) gaseous fluoride and SO2 concentration in the outdoor air in Mangbu Township area was 0.51 μg dm−2⋅day and <0.05 mg m−3, respectively and in Xiaolongdong Township was 2.7 μg dm−2 day and <0.05 mg m−3, respectively while in Zhaotong City these concentration were lower than the ambient air standard (3 μg dm−2⋅day and 0.5 mg m−3, respectively). (2) The indoor gaseous fluoride concentration (3.7 μg m−3) in air of kitchen with the improved coal stove was within the reference value (10 μg m−3); SO2 concentration (0.94 mg m−3) in kitchen air had decline, but its concentration was still higher than indoor air quality standard (0.5 mg m−3). (3) Average concentration of gaseous fluoride and SO2 in air of traditional flue-curing barn of Xiaolongdong Township was 7.2 μg m−3 and 6.8 mg m−3 respectively, and in Yujiawan village were 10.1 μg m−3 and 14.4 mg m−3, respectively. (4) After using the calcined dolomitic siliceous limestone instead of clay mixed with coal, gaseous fluoride and SO2 concentration in the traditional flue-curing barn air decreased of 45% and 91%, respectively. The gaseous fluoride and SO2 pollution in the traditional flue-curing barn is very serious. The corn and chili baked by open stoves in traditional flue-curing barn (baking room) was also seriously polluted by fluoride and sulfur. After using the calcined dolomitic siliceous limestone instead of clay mixed with coal, gaseous fluoride and SO2 concentration in the traditional flue-curing barn air have declined markedly. The way of adding calcined dolomitic siliceous limestone instead of clay as a binder for briquette-making is an economically feasible way to control the indoor pollution of fluorine and sulfur in coal-burning endemic in Zhaotong, Yunnan.