The main focus here in terms of pollutants is on criteria pollutants, especially sulfur dioxide (SO2) and oxides of nitrogen (NOx) but also including carbon monoxide (CO), particulate matter (PM) with an aerodynamic diameter smaller than about 10 micrometers (µm) (PM10), and PM with an aerodynamic diameter smaller than about 2.5 µm (PM2.5). An ozone precursor of volatile organic compounds (VOCs) is also included.

With respect to identifying technology options, the focus here is on the current status of emission-source technologies and current options for repair and replacement. However, because technology changes over time, explicit consideration is given to the process of technology change and the implications for technology change in the future. Furthermore, we consider both pollution control and pollution prevention technologies. Typically, “pollution control” refers to “end-of-pipe” techniques for removing pollutants from an exhaust gas after the pollutants have been formed in an upstream process. For example, in a coal-fired power plant, pollutants such as NOx, SO2, and PM are formed during combustion. Postcombustion control technologies such as selective catalytic reduction, fuel gas desulfurization, and electrostatic precipitation, respectively, can be used to reduce or capture these pollutants. In contrast, pollution prevention approaches are aimed at reducing or eliminating sources of pollution, typically through feedstock substitutions or process alterations. For example, in the case of a coal-fired power plant, methods that more carefully control and stage mixing of fuel and air can prevent the formation of a portion of NOx that otherwise would have been created. As another example, evaporative VOC emissions can be prevented by substituting water-based solvents for VOC-based solvents used at a manufacturing facility. A way to evaluate the effect of pollution prevention measures is to compare emissions and energy use with those of a more traditional feedstock or facility design.

In addition, cost is always a consideration when evaluating and choosing options for repair and replacement. Therefore, cost implications of alternatives for repair and replacement are summarized.


The purpose of this section is to identify and evaluate the frequency of NSR permitting activity with respect to industrial categories for the purpose of determining which emission sources represent the highest priority for assessment. However, a substantial challenge is that there is

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