Development of Atmospheric Tracer Methods To Measure Methane Emissions from Natural Gas Facilities and Urban Areas

Abstract

A new, integrated methodologyto locate and measure methane emissions from natural gas systems has been developed. Atmospheric methane sources are identified by elevated ambient CH4 concentrations measured with a mobile laser-based methane analyzer. The total methane emission rate from a source is obtained by simulating the source with a sulfur hexafluoride (SFS) tracer gas release and by measuring methane and tracer concentrations along downwind sampling paths using mobile, real-time analyzers. Combustion sources of methane are distinguished from noncombustion sources by concurrent ambient carbon dioxide measurements. Three variations on the tracer ratio method are described for application to (1) small underground vaults, (2) aboveground natural gas facilities, and (3) diffuse methane emissions from an entire town. Results from controlled releases and from replicate tests demonstrate thatthe tracer ratio approach can yield total emission rates to within approximately &15%. The estimated accuracy of emission estimates for urban areas with a variety of diffuse emissions is &50%.

Natural gas facility methane emissions: measurements by tracer flux ratio in two US natural gas producing basins

“…The tracer flux ratio method (sometimes "tracer release" or "tracer method") involves releasing known quantities of tracer gas(es) close to a suspected source at a facility (Lamb et al, 1995;Roscioli et al, 2015). In this study, N 2 O and C 2 H 2 were used as tracer gases to measure CH 4 emissions.…”

“…The ratios of measured species' mixing ratios, combined with known tracer release rate, determine emission rates. Such methods have been in use since the 1990's (Lamb et al, 1995;Shorter et al, 1997), and unlike dispersion methods, tracer flux ratio measurements do not require knowledge of atmospheric stability and transport, and are independent of exact wind measurements and their timescales (Mønster et al, 2014;Roscioli et al, 2015). The use of two tracers allows for a self-contained quality check for each measurement (Allen et al, 2013;Roscioli et al, 2015).…”

Emissions from oil and gas operations in the United States and their air quality implications

“…Ground-level measurements, made downwind of petroleum and natural gas supply chain sites, have been made using a variety of techniques designed to infer emission rates from ambient concentrations. A procedure that enables some of the most precise measurements is generally referred to as a tracer technique (Lamb et al, 1995;Shorter et al, 1997;Kolb et al, 2004;Herndon et al, 2005Herndon et al, , 2013Allen et al, 2013). In this method, tracer compounds (e.g., SF 6 , N 2 O, C 2 H 2 ) are released at a known rate at or near an emission source; downwind measurements of the target pollutant (minus background) and the tracers (minus background) are equal to the ratio of emission rates, if the dispersion of the target pollutant and the tracer are identical.…”

Methane emissions from above ground open manure slurry tanks

“…Calculation of the CH 4 source strength resulted in estimates within 14% of the true emission strength, and no significant difference was found in emission estimates between colocated and separated sources. It was concluded that the tracer underwent adequate mixing with the CH 4 at those length scales [Lamb et al, 1995]. Thus, as long as both plumes are approximately coincident, SF 6 is a suitable tool in simulating the diffusion of methane.…”