Reply to “Reply to ‘Comment on “Hydrocarbon emissions characterization in the Colorado Front Range – A Pilot Study”’ by Michael A. Levi” by Gabrielle Pétron et al.

The reply by Pétron et al. (2012a) to my comment, Levi (2012), on their paper, Pétron et al. (2012a), defends their original conclusion: fugitive emissions in an area that they observed in 2008 were likely larger than those indicated by previous estimates. The reply also claims to have now better characterized the uncertainties in their and my approaches. In particular, they question the representative nature of a data set that Pétron et al. (2012) relied on, and that Levi retained, although they do not recalculate their estimates. Pétron et al. (2012) also claim to show that the analysis in Levi (2012) is flawed because, they argue, it implies the physically unrealistic conclusion that fugitive emissions from the natural gas operations that Pétron et al. (2012) studied may be negative. Pétron et al. (2012a) are reasonable to be skeptical of the data set that they highlight. I show in this reply that if that data set is indeed not representative of condensate tank flashing in the area under study, it is impossible to produce the results in Pétron et al. (2012a) that the authors now defend. I also show that the other critique of Levi (2012) offered by Pétron et al. (2012a), i.e., that Levi's analysis has physically unrealistic implications, relies on an incorrect interpretation of the formulas in that comment. Only one of two conclusions is possible: the results in Levi (2012) are correct, or the conclusions in both Levi (2012a) and Pétron et al. (2012a) are unjustified.