Method disagreement could be compounded by changing operating states during the measurement period. Eliminating the 3 facilities where the operating state changed during measurement increased the fraction of comparisons that agree by ≈3%, from 2 of 28 to 2 of 20, and decreased the fraction of comparisons that disagree by a similar amount; this is likely not a signicant source of disagreement between methods. See Table , column "State Change" for the specic facilities. While emissions could change while the facility is in one operating state, operational knowledge indicates that large changes were unlikely. Therefore, since both methods measured when emissions were essentially stable, it is likely that the TD methods, in eld conditions at midstream facilities, have uncertainties larger than indicated by controlled testing, likely due to multiple emission sources and complex wind elds at these facilities.