Good Practice Guidance and Uncertainty Management in National Greenhouse Gas

The purpose of this paper is to support the development of so-called good practice guidelines for the estimation of methane (CH4) emissions from solid waste (SW) disposal for national greenhouse gas inventories. The paper reviews and discusses the emission estimation methods given in the IPCC 1996 Revised Guidelines (IPCC Guidelines), and uncertainty and quality management issues related to the emission estimation. At solid waste disposal sites (SWDS) the degradable organic carbon in waste is decomposed by bacteria under anaerobic conditions into methane (CH4) and other compounds. The CH4 emissions from SWDS are important contributors of global anthropogenic CH4 emissions. The IPCC Guidelines give two methods for estimation CH4 emissions from solid waste disposal. The IPCC default method is a simple mass balance calculation which estimates the amount of CH4 emitted from the SWDS assuming that all CH4 is released the same year the waste is disposed of. The other method outlined in the IPCC Guidelines is the so-called First Order Decay (FOD) method. The FOD method takes the time factors of the degradation process into account, and produces annual emission estimates that reflect this process, which can take years, even decades. The estimates on annual emissions produced by the two methods are therefore not comparable. The FOD method produces better estimates on annual emissions, whereas the IPCC default method has merits e.g. in studies comparing the potential to reduce the CH4 emissions by alternative waste treatment methods. The use of the IPCC default method and FOD method require as input annual SW disposal data including information on the composition of the waste and on the conditions at the SWDS. The IPCC default method requires this data only for the inventory years, whereas the FOD method requires data for also the past 20-25 or more years. In addition, the rate of degradation for waste disposed at SWDS needs to be determined in the FOD method. The IPCC Guidelines contain default values for most of the data needed in the use of the default method, whereas the guidance and default values needed in the use of the FOD method are insufficient. The uncertainties in the emission estimates produced by both the IPCC method and the FOD method are large in most countries. Even few industrialised countries have good SW disposal data based on weighing of amounts disposed and frequent sampling to determine the composition of waste at the SWDS. The SW disposal data in many developing countries is especially poor and some concern is expressed also on the suitability of some of the default parameters in their conditions. More frequent aerobic decomposition, scavenging and fires in the conditions prevailing in many developing countries may cause much lower emissions from SW disposal than in industrialised countries. Improvements in activity data collection and emission factors (parameters used in the calculation) are needed in many countries. Also some of the IPCC default values should be reviewed and updated.