StacksVerified U.S. regulatory reference

40 CFR Part 72, Appendix C

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov

The equation used to calculate the yearly SO2 emissions (SO2) is as follows:

If gas is the only fuel, gas emissions are defaulted to 0.

Each fuel type SO2 emissions is calculated on a yearly basis, using the equation:

For coal, the yearly fuel burned is in tons/yr and the AP-42 factor (which accounts for the ash retention of sulfur in coal), in lbs SO2 ton coal, is by coal type:

Coal typeAP-42 factor
Bituminous, anthracite39 lbs/ton
Subbituminous35
Lignite30

For oil, the yearly fuel burned is in gal/yr. If it is in bbl/yr, convert using 42 gal/bbl oil. The AP-42 factor (which accounts for the oil density), in lbs SO2/thousand gal oil, is by oil type:

Oil typeAP-42 factor
Distillate (light)142 lbs/1,000 gal
Residual (heavy)157

For all fuel, the units conversion factor is 1 ton/2000 lbs.