| ULE | Ultra-low Emission |
| DID | Difference-in-Difference |
| Btu | British Thermal Unit |
| SO2 | sulfur dioxide |
| NOx | nitrogen oxide |
| kWh | kilowatt hour |
| tce | Ton (Tonne) of Coal Equivalent |
| Obs | number of observations |
| Mean | mean value |
| St.d | standard deviation |
| Min | minimum value |
| Median | Median value |
| Max | maximum value |
| R2 within | goodness of fit within the group |
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