University of California Press

Figure 1.

Dashed vertical lines at 91% and 97% CH4 content show thresholds associated with the reported, possible malfunction of the Bacharach Hi Flow® Sampler (BHFS) used to make these measurements (Howard et al., 2015; Howard, 2015b). Summarized above the figure are our calculations of the mean emission rate of the complete, unfiltered dataset (0.11 scfm) and of the subsets obtained by filtering out measurements below 91% and 97% CH4 content (0.15 and 0.19 scfm, respectively). Because BHFS malfunction has not been reported to occur for sources with CH4 content >97%, our analysis assumes such measurements are unaffected. We thus use the 80% difference in mean CH4 emissions between the full dataset and the filtered subset >97% CH4 content (i.e., 0.19 vs 0.11 scfm) to constrain the potential impact of BHFS malfunction on the results of BHFS-based measurements in Allen et al. (2013a). Symbols indicate the region where measurements were made: AP=Appalachian (circles); GC=Gulf Coast (squares); MC=Midcontinent (triangles); RM=Rocky Mountains (crosses). Vertical axis units are standard cubic feet per minute (scfm).

Measurements of CH₄ emissions from equipment leaks at natural gas production sites as reported in Allen et al. (2013a, 2013b).

Dashed vertical lines at 91% and 97% CH₄ content show thresholds associated with the reported, possible malfunction of the Bacharach Hi Flow^® Sampler (BHFS) used to make these measurements (Howard et al., 2015; Howard, 2015b). Summarized above the figure are our calculations of the mean emission rate of the complete, unfiltered dataset (0.11 scfm) and of the subsets obtained by filtering out measurements below 91% and 97% CH₄ content (0.15 and 0.19 scfm, respectively). Because BHFS malfunction has not been reported to occur for sources with CH₄ content >97%, our analysis assumes such measurements are unaffected. We thus use the 80% difference in mean CH₄ emissions between the full dataset and the filtered subset >97% CH₄ content (i.e., 0.19 vs 0.11 scfm) to constrain the potential impact of BHFS malfunction on the results of BHFS-based measurements in Allen et al. (2013a). Symbols indicate the region where measurements were made: AP=Appalachian (circles); GC=Gulf Coast (squares); MC=Midcontinent (triangles); RM=Rocky Mountains (crosses). Vertical axis units are standard cubic feet per minute (scfm).

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