While the daily BU estimates may not accurately reect emissions at the facility (see Brown et al. 1 ), changes in the BU estimate provide an estimate of how emissions likely diered between baseline and EOP based on operational conditions which is independent of either TD method. Most BU estimates in this study utilized prior onsite direct measurements of emissions (stack tests, high-ow sampler, etc.) rather than emission factors, and are therefore site-specic estimates. As a result, facilities may have the same number of compressors operating in both baseline and EOP deployments, but have dierent compressors running, creating substantially dierent BU emissions estimates.