Towards accurate quantification of New Zealand’s methane emissions from waste and agriculture

Methane emissions from waste and agriculture account for 46.6 % of Aotearoa New Zealand’s (ANZ) gross greenhouse gas emissions in 2023. Despite the significance of methane emissions, the only way to estimate their magnitude is based on emission factor methods, which include large uncertainties. We present newly developed tools to directly measure methane emissions from wastewater treatment facilities, animal effluent storage systems and herds of dairy cows. We deploy in situ analysers on mobile observation platforms (vehicle and drone) and quantify methane emission fluxes using the tracer gas technique. The accuracy of this method is estimated in multiple ways: i) a controlled release experiment, ii) through comparison to a mass-balance modelling approach, iii) through comparison to co-located chamber measurements for methane emissions from effluent ponds, iv) through comparison to co-located measurements of animal emissions using the “GreenFeed” technique. The comparisons show excellent agreement, providing much needed assurance of analytical performance to our mobile techniques. Our tools support ANZ’s farmers and waste managers to better understand current emissions, as well as to assess the efficacy of investments into emission mitigation. Additional tests explore new isotope techniques with the goal to quantify methane fluxes from different components within a plant, for example methane derived from digestors versus methane derived from biosolids in wastewater treatment systems, or methane from the open face of a landfill versus emissions from an area that is covered.