Power generation technology options also differ widely on how much they can pollute the air, at least without appropriate environmental controls in place. A big part of the reason for the number of regulations and policies put in place that penalize power plants burning fossil fuels (and reward power generated from wind and solar) is the large social cost of air pollution. Emissions of oxides of sulfur and nitrogen degrade air quality in cities, and emissions of carbon dioxide contribute to global climate change. A comparison of some of the air quality impacts of power generation technologies is shown in Table 2.
The air emissions figures in Table 2 don’t really present the whole environmental impact, however – they just measure how much pollution comes from the plant’s smokestack. Any fuel, however, has to be harvested from the ground (or sun or sky), possibly refined to remove impurities, and transported. All of these other stages of the “life cycle” of fuels for power generation have environmental impacts. Compared to the environmental impacts of burning fuel in a power plant, however, most of these other life-cycle impacts are probably pretty small. Figure 6 shows an example for Pennsylvania’s power grid. The figure shows the contribution of the life cycle of different fuels to the total quantity of greenhouse gases emitted in Pennsylvania (one of the largest electricity-producing states in the U.S.). More than 80% of the greenhouse-gas emissions from electricity production in Pennsylvania is due to the burning of coal in power plants. Mining, processing and fuel transportation impact Pennsylvania’s environment in other ways but add very little to the overall quantity of greenhouse gases.