US regulators are proposing to weaken air quality laws, which would allow new coal-fired power plants to pollute US parks from Shenandoah in Virginia to the Great Basin in Nevada, a new report said on Thursday. Amid rising power demand and flat US natural gas output, electricity generators are seeking to build power plants fired by abundant coal. The fuel is cheap compared with other fossil fuels, but emits more pollutants, such as mercury and smog components sulfur dioxide and nitrogen oxides, as well as the greenhouse gas carbon dioxide.