The in-stack tracer method was used during the field campaign to measure unburned methane entrained in the exhaust of natural gas compressor engines ("combustion slip"). Combustion slip was estimated by injecting a tracer gas into the exhaust stream at a known flow-rate and measuring concentrations of both the tracer gas and methane at the exhaust stack exit. The total exhaust flow was estimated from the diluted tracer gas concentration measured at the exhaust stack exit.
