Q553. When using Calculation Method 2 to calculate vented CO2 emissions from an AGR unit (Equation W-3), what are the required units of measure for the calculated CO2 emissions? May we use a flow meter to calculate annual emissions of CO2?

A553. The units of measure for E_a,CO2, the annual volumetric CO₂ emissions at actual conditions calculated in Equation W-3, are cubic feet per year. If you wish to use the methodology set forth in 40 CFR 98.233(d)(2), then yes, a vent flow meter must be used to determine the total annual volume of vent gas flowing out of the AGR unit (V_s in Equation W-3). The units of measure for the total annual volume of vent gas are actual cubic feet per year. As an alternative to determining the volumetric emissions at actual conditions, the introductory paragraph in 40 CFR 98.233 allows for the calculation directly in standard cubic feet per year if the flow meter determines the volume at standard conditions. (Effective January 1, 2025 (i.e., beginning with Reporting Year 2025), you must provide the temperature and pressure that correspond to the measured total annual volume of vent gas (40 CFR 98.236(d)(2)(i)(D) and (E), respectively).)

If the volumetric emissions are determined at actual conditions, 40 CFR 98.233(d)(9) (40 CFR 98.233(d)(10) beginning on January 1, 2025) requires that the volumetric emissions of Equation W-3 be converted to standard conditions using the methods in 40 CFR 98.233(t). 40 CFR 98.233(d)(10) (40 CFR 98.233(d)(12) beginning on January 1, 2025) then requires that the volumetric emissions of Equation W-3 in standard conditions be converted into mass emissions using the methods in 40 CFR 98.233(v).  You must report emissions in metric tons of CO₂ to meet the reporting requirements in 40 CFR 98.236(d)(1)(v).