It was caused by local pollution.
adopting pollution prevention and control technologies sufficient to permit the enterprises to comply with national or local pollution discharge standards and total volume control quotas for pollutants.
"Clean coal" is a term coined by the industry decades ago, referring to its efforts to reduce local pollution.
Even the telephone numbers of many government bureaus are secret, and until the late 1990s, local pollution indices were often classified as neibu to avoid embarrassing the authorities.
In India the gains from the Green Revolution are already shrinking because of local pollution, global warming and waning resistance to pests and disease.
Coal from the Powder River Basin of Montana and Wyoming tends to be low in sulfur, for example, allowing power plants to burn more without exceeding local pollution limits.
