Characterization of acidity and sulfate in dust obtained from the Wuda coal base, northern China: spatial distribution and pollution assessment.

The coal fire in Wuda, Inner Mongolia of China, is one of the most serious coal fires in the world with a history over 50 years and endangers the neighboring downwind urban area. A lack of effective measures to control coal fires in this region can aggravate environmental pollution. In this study, the levels and spatial distributions of acid (pH) and SO42- in dust in the Wuda coalfield and its surrounding areas in Inner Mongolia, North China, were reported to identify the potential acid and SO42- pollution in the local environment with an area of 270 km2. The mean pH and SO42- content was to found to be 7.44 and 5981 μg·g-1, respectively. Through the analysis of the spatial distribution of pH and SO42- concentrations, it was found that most of contaminated areas are mainly distributed in coalfield and its affiliated industrial parks, and the Wuda urban area also suffered from pollution. Based on chemical equilibrium, the surface acid pollution might have resulted in the change of the dust type from the original weakly alkaline CaCO3 type to the CaSO4 type in coalfield and industrial parks. Finally, the pollution assessment revealed that the coalfield and industrial parks are both at heavy pollution levels, and the urban area is mostly moderately polluted, followed by farm and peripheral region with a certain pollution risk. The results indicated that the long-term release of acidic gas from the coal fires and industrial parks can led to significantly elevated acidity and SO42- levels in the dust of the local environment, while coal fires can aggravate surface pollution in industrial parks, but the extent of contamination was also closely related to the terrain and wind direction in the study area.