Researchers in California, Oregon and Washington noticed specks of sulfur compounds, carbon and other byproducts of coal combustion coating the silvery surfaces of their mountaintop detectors.

• 研究人员在加里福尼亚、勒冈、盛顿发现硫化物、及其他燃烧副产品在其山顶的银色探测器上留下了斑点。