Ozone Season Performance Grades

First Annual Report Card for Coal-fired Power Plants in The Eastern United States

This page presents the first annual report card for the performance of coal-fired power plants across the eastern United States. The Report card covers coal-fired Electricity Generating Units (EGUs) that have installed advanced nitrogen oxide (NOx) pollution control technologies. Many of these EGUs have already spent billions of dollars on advanced technology to control NOx, yet they do not always use the technology effectively. This is especially important during the summer months when NOx can combine with sunlight and heat to form ground-level ozone or smog. Research shows that ozone is often transported - by westerly and southerly winds - into the northeast from upwind states at levels that are already approaching the 70 parts per billion ozone standard.

The report card covers 323 coal-fired EGUs that have already installed advanced NOx control technology. The report card focuses on EGUs in the eastern U.S. and is based on the actual emissions reported by sources to the EPA's Clean Air Markets Division (CAMD).

MDE's analysis demonstrates that by running pollution controls effectively throughout the 2017 ozone season (May-September) up to 400 tons of NOx emissions per day could have been reduced. This equates to over 46,000 tons of NOx emissions reductions that could have been reduced over the 153-day ozone season. The data for this analysis is available by clicking here. The report is available here.

2017 Ozone Season Total NOx Emissions:

Actual and Best Rates

Data submitted to the CAMD shows that the use of control technologies varies by state, with many units in some states performing well and many units in other states consistently performing poorly. 28 states were analyzed in 2017. 

Mouse over the states in the map below to view the performance status. Click on a state shaded in either red for states exceeding best historical rates or blue for states that are optimizing controls to see data for the facilities that were part of this study. To zoom in on individual facilities, click and drag your mouse over the chart. For additional information on individual units included in the study, click here.

Determining Letter Grades

The methodology to distribute letter grades to individual EGUs builds from Maryland's 2017 ozone season analysis of control optimization at coal-fired EGUs with Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR) controls across the eastern United States. MDE developed a grading system based on individual EGU performance rates.

Binning Methodology

MDE assessed SCR/SNCR control optimization for a specific year by comparing ozone season data for that year to a series of NOx emission rates reflecting various levels of optimization for each unit. These optimized rates are derived from the unit's 2005-2016 ozone season data (adjusted if controls were installed after 2005), available in the EPA's Air Market Programs Database. For initial screening, the lowest ozone season average NOx emission rate was selected for each unit. If the unit installed an SCR or SNCR in 2005 or a later year, the data collection period was narrowed to the first ozone season in the year following the installation to 2016.

A deviation percentage was then calculated for each unit by dividing the current ozone season average emission rate by the identified best ozone season average emission rate. Units were then subdivided into three categories, or bins, based on the calculated percent deviation. Each of these bins represents a different level of optimization based on the unit's own previously demonstrated performance. 

Table 1. Description of Three Bins for EGU Optimization Performance

Bin Percent Deviation Description​
1 <0% 2017 NOx rate is less than past best rate. Equal or better performance compared to past
2 0-100% 2107 NOx rate is greater than past best rate but less than double. Slightly poorer performance compared to past
3 >100% 2017 NOx rate is more than double past best rate. Noticeably poorer performance compared to past 

Grading Scale

While MDE's binning methodology allows comparison of a unit's control performance in a particular year to its own previously demonstrated capabilities, it does not allow comparison of units to each other. In order to assign a letter grade to each unit, MDE used the binning methodology in conjunction with performance rates for SCR and SNCR technologies to provide an indication of the unit's overall efforts to optimize controls. The following charts illustrate the methodologies used for grading EGU units. The methodologies are identical, but with different rate performance standards for SCR and SNCR units. Under this methodology, any SCR unit that achieved a 2017 rate less than 0.10 lb/mmBtu and any SNCR unit under 0.15 lb/mmBtu would receive a grade of A or A+ depending on their designated bin.

Grading Strategy for SCR Units


Grading Strategy for SNCR Units


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