Methane and nitrous oxide emission factors for windrow composting of garden waste in Denmark based on ground-based remote sensing measurements

National methane and nitrous oxide emission factors for composting garden waste were determined using ground-based remote sensing. Emission factors were determined to enable lifecycle assessment studies on alternative treatment options for garden waste management. Four emission measurement campaigns were performed at each site over a calendar year, to account for seasonal variation in emissions. Average emission rates varied between 0.47 to 10.8 kg CH₄ h^-1 and 0.01 to 0.14 kg N₂O h^-1. The highest emission rates were observed at the locations with most waste on-site. Compiling these observations with results from recent, similar measurement campaings at Danish composting facilities, average emission factors of 2.54 kg CH₄ and 0.058 kg N₂O per ton waste treated were obtained. Both proposed emission factors are lower than the national emission factors considered in the most recent National Inventory Report from Denmark, which were derived from observations at a single site.