Progress Report - Emission Controls and Monitoring
Emission Controls and Monitoring
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Last updated on November 21, 2024
Data current through 2023
ARP and CSAPR SO2 Program Controls and Monitoring
Sources have a number of options to control emissions of SO2, NOX, and hazardous air pollutants (HAPS) including mercury. Under Acid Rain Program (ARP) or the Cross-State Air Pollution Rule (CSAPR) programs, sources may reduce SO2 emissions by switching to low sulfur coal or natural gas, employing various types of flue gas desulfurization (FGDs, or scrubbers), or, in the case of fluidized bed boilers, injecting limestone into the furnace. FGDs on coal-fired electricity generating units are the principal means of controlling SO2 emissions.
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- Units with FGD controls accounted for 75.2 percent of coal-fired units and 83.6 percent of coal-fired electricity, measured in megawatt hours, or MWh, in 2023.
- In 2023, 16.4 percent of the CSAPR units (including 100 percent of coal-fired units) monitored SO2 emissions using CEMS. 99 percent of SO2 emissions were measured by CEMS.
CSAPR NOX Annual Program Controls and Monitoring
To control NOX emissions under these programs, sources can employ advanced post-combustion controls such as selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR), as well as combustion controls, such as low NOX burners.
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- 83.1 percent of fossil fuel-fired generation was produced by units with advanced add-on controls (either SCR or SNCR).
- In 2023, the 211 coal-fired units with advanced controls (either SCRs or SNCRs) generated 80.5 percent of coal-fired electricity. At oil- and natural gas-fired units, SCR- and SNCR- controlled units produced 84.9 percent of electricity.
- In 2023, 66.3 percent of the CSAPR units (including 100 percent of coal-fired units) monitored NOX emissions using CEMS. 97.1 percent of NOX emissions were measured by CEMS.
CSAPR NOX Ozone Season Program Controls and Monitoring
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- 73.5 percent of all the fossil fuel-fired generation was produced by units with advanced add-on controls (either SCRs or SNCRs).
- In 2023, 190 units with advanced add-on controls (either SCR or SNCR) accounted for 72.2 percent of coal-fired electricity. At oil- and natural gas-fired units, SCR- and SNCR-controlled units produced 74.1 percent of electricity.
- In 2023, 74.3 percent of the CSAPR units (including 100 percent of coal-fired units) monitored ozone season NOX emissions using CEMS. 96.3 percent of ozone season NOX emissions were measured by CEMS.
MATS Controls and Monitoring
Sources in MATS can improve operation of existing controls, add pollution controls, and switch fuels (including coal blending). Specific pollution control devices that reduce mercury include wet FGDs, activated carbon injection (ACI), dry sorbent injection (DSI), and fabric filters.
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- In 2023, 47 percent of the MATS units reporting mercury emissions and 54 percent of the electricity at the MATS reporting units used activated carbon injection (ACI), a mercury-specific pollution control method to reduce mercury emissions and SO2.
- About 96 percent of units that reported continuous mercury emissions data (or 98 percent of the total electricity from units that reported data) reported the use of advanced controls, such as wet scrubbers, dry scrubbers, or ACI, to reduce hazardous air pollutant emissions in 2023. These controls also reduce other pollutants, including SO2. Some oil-fired units can meet the MATS emission limits through the use of particulate matter (PM) controls such as electrostatic precipitators (ESPs) or fabric filters (FFs).
Mercury Compliance and Monitoring Methods used by Units Reporting Hourly Data under MATS, 2023
| Reporting Hourly Data | Compliance Method (# of Units) | Monitoring Method | ||||
|---|---|---|---|---|---|---|
| Number of reporting units | Number of reporting facilities | Electrical Output | Heat Input | Sorbent Trap | CEMS | CEMS and Sorbent Trap |
| 352 | 161 | 97 | 255 | 150 | 166 | 36 |
EPA has developed detailed procedures codified in federal regulations (40 CFR Part 75) to ensure that sources monitor and report emissions with a high degree of precision, reliability, accuracy, and timeliness. Most EGUs must continuously monitor their emissions of SO2, NOX, and CO2. For EGUs that burn coal or other solid fuel, this can be done with continuous emission monitoring systems (CEMS) to measure SO2, NOX CO2, and mercury or sorbent trap monitoring systems for mercury. Most EGUs that burn natural gas or oil have the option of continuously measuring fuel quantity and evaluating fuel quality to determine SO2 and CO2 emissions. Some qualifying units with low emissions can conduct periodic stack tests in lieu of continuous monitoring.
Sources must also conduct stringent quality assurance tests of their monitoring systems to ensure the accuracy of emissions data and to provide assurance that a quantity of emissions measured at one facility is equivalent to the same quantity measured at a different facility. EPA conducts comprehensive electronic and desk data audits to validate the reported data. The hourly CEMS data consists of greater than 99% quality assured measurements and less than 1% calculated values used to provide a complete record of all emissions. For more information on substitute data refer to Substitute data in EPA CAPD's Power Sector Emissions Data (pdf)