Please find the attachment.

Methodology and uncertainty estimation for measurements of

methane leakage in a manufactured house

Anna Karion, Michael F. Link, Rileigh Robertson, Tyler Boyle, Dustin Poppendiec

Top-down (atmospheric) and bottom-up (inventory) methods of determining greenhouse gas emissions are complementary approaches, with the goal of providing feedback as to the most effective mitigation strategies.  There is a significant discrepancy between these approaches for methane, and in-home emissions are probably a major contributor.  The EPA methane inventory now includes an estimate of these emissions, but the emission factors are all based on one study.  This manuscripts documents controlled release experiments to optimize the methods to determine these emission factors and to quantify the uncertainty using the mass balance method which quantifies whole-house emissions rates as a sum of all of the leaks in the house.  This work is an important first step, laying the groundwork for future studies of different types of homes in different cities (with different types and ages of infrastructure) and in different climates.  The manuscript is well-organized and well-written and I feel it should be published with very minor changes. 

Abstract:  Don’t need to specify “recently” AND “latest”. 

Section 2: Confusing wording to discuss the overall 3-part plan in the previous paragraph and then specify measuring whole-house emissions rates of methane (part 2 of the plan) as the first sentence of the methods.  Suggest changing ” We measured whole-house emission rates of methane in a manufactured …” to a more general statement along the lines of “We performed the controlled experiments described above in a manufactured house…” 

Section 2.1: “A flush pump pulled air at 10 L min-1 through whichever inlet line the valve was set to.” Awkward  wording. Maybe “through the appropriate inlet line”

I’m confused about the flowrates but I think it’s just that there are three total tubes: indoor for CO2/CH4, outdoor for CO2/CH4, and indoor for SF6.  First two lines: 10 L/min flush, CRDS sipping.  Third line: PTR-MS flowrate of 15 L/min with inlet flowrate of 120 mL/min.  Should this be PTR-MS flush rate of 15 L/min with inlet flowrate of 120 mL/min?

The gas heating component of the furnace and the HVAC gas heating element are the same things, so the sentences in lines 113-115 in this section were confusing to me.  I think the tracer experiments were in October(?) and then the heating element was turned on in December during quiescent emissions measurements. 

How far away is the weather station in Arlington, VA?

It’s obvious, but consider specifying that the windows were closed.

Section 2.3: You used mean indoor, but median outdoor.  I’m not sure which is correct here. The spikes are real, so isn’t the mean more appropriate since some of that air exchanges with the indoor air? During the afternoon, it’s hopefully a small difference.  How different would the results be if you used mean for outdoor? 

Section 2.6:  For the first experiment, does the ERquiescent have to be taken into account?  I see that you do mention that in Section 3.2  (This should be moved to the methods.)

Section 3.1 You didn’t find any correlation with wind speed like Nabinger et al did?

Fig 6:  maybe should expect error bars to be larger on the blue symbols (low ACR)

Fig 6: The average seems lower in October than the rest of the analysis period.

Line 302 in Section 3.3 Consider rewording “The electric house cooling system was in operation with the heating system disabled for most of the study, including for all the tracer injection experiments.”to “ The electric house HVAC system was in operation for all of the study, with the heating system disabled for most of the study, including for all the tracer injection experiments.  “ or something along those lines.