Overview of ETS/CEM Data

Under Title IV of the Clean Air Act Amendments of 1990 (CAAA), Congress established an innovative program using emissions trading and similar incentive-based regulatory strategies to reduce emissions from electric utilities, requiring the utilities to monitor and report hourly NOx emission rate, SO2, and CO2 emissions, and heat input data to EPA.

As of January 1, 1994, the larger coal-fired units, designated Phase I units, were required to report hourly emissions data to EPA's Emissions Tracking System/Continuous Emissions Monitoring (ETS/CEM).  Starting in January 1, 1995, Congress also required reporting by all the other units affected by Title IV, the Phase II units;  EPA made exceptions by providing six- month extensions to units reporting NOx emissions by oil- and gas-fired units and for units located in ozone nonattainment areas, and one-year extensions to units located in ozone attainment areas.  Note that NOx data may not be complete for 1995, in light of these extensions.

Coal-fired units are required to use CEMs to monitor emissions.  However, other units can use alternate methods to measure their data.  Oil- and gas-fired units have the option to use CEMs or to measure fuel flow hourly and estimate SO2, CO2, and heat input based on fuel sampling; for NOx, only oil- and gas-fired peaking units are allowed to use hourly estimation procedures (based on heat input) instead.

Hourly, quarterly, and annual data are reported quarterly to EPA's Emission Tracking System ETS/CEM in ASCII files formatted according to the requirements contained in the Electronic Data Reporting (EDR) V1.3 (EPA, 1995).  Because the reporting requirements are new and complicated, it takes time for the reporting to be completely accurate; each year, the data quality improves over the previous year.