Code of Federal Regulations Title 40. Protection of Environment 40 CFR Pt. 72, App. A—METHODOLOGY FOR ANNUALIZATION OF EMISSIONS LIMITS

For the purposes of the Acid Rain Program, 1985 emissions limits must be expressed in pounds of SO₂ per million British Thermal Unit of heat input (lb/mmBtu) and expressed on an annual basis.

Annualization factors are used to develop annual equivalent SO₂ limits as required by section 402(18) of the CAA. Many emission limits are enforced on a shorter term basis (or averaging period) than annually. Because of the variability of sulfur in coal and, in some cases, scrubber performance, meeting a particular limit with an averaging period of less than a year and at a specified statutory emissions level would require a lower annual average SO₂ emission rate (or annual equivalent SO₂ limit) than would the shorter term statutory limit. EPA has selected a compliance level of one exceedance per 10 years. For example, an SO₂ emission limit of 1.2 lbs/MMBtu, enforced for a scrubbed unit over a 7–day averaging period, would result in an annualized SO₂ emission limit of 1.16 lbs/MMBtu. In general, the shorter the averaging period, the lower the annual equivalent would be. Thus, the annualization of limits is established by multiplying each federally enforceable limit by an annualization factor that is determined by the averaging period and whether or not it's a scrubbed unit.