In June 1992 more than 150 countries signed the United Nations Framework Convention on Climate Change (UNFCCC) at the Earth Summit in Rio de Janeiro. The Convention entered into force in 1994 after 50 signatories had officially ratified the agreement. UNFCCC requires signatories to prepare inventories of their greenhouse gas emissions sources and sinks. While Ukraine was the 6th largest emitter of greenhouse gases among Annex I (developed) countries. Ukraine submitted its first draft inventory to the UNFCCC Secretariat in autumn 1998. Monitoring and reporting greenhouse gas emissions are both key elements of compliance under the UNFCCC, which requires that Ukraine constantly investigates and develops inventories and monitors emissions.

Compliance with UNFCCC requirements is a compulsory precondition of Ukraine's participation in the international process of GHG mitigation. This will allow Ukraine to significantly improve the energy efficiency of its economy.

Two factors impede Ukraine's ability to prepare accurate inventories of GHGs. The first is the lack of statistical data, which makes it extremely difficult to prepare transparent IPCCcompatible inventories. The second is lack of knowledge about global climate change and the purpose and methodology of greenhouse gas inventories at the local level, where data are initially collected.

The documents of the Intergovernmental Panel on Climate Change (IPCC) show that the solid waste (SW) sector contributes from 5 to 20% into global anthropogenic methane emissions (IPCC, 1996). Preliminary estimates showed that the SW sector in Ukraine generated approximately 4.3% of the total volume of ÑÎ2-equivalent emissions in 1990.

The SW sector is a key source category of GHG emissions in Ukraine.

In order to assist a GHG inventory in Ukraine, Proposals to a Concept of the Ukrainian National GHG Inventory System have been developed. This document suggests the terms and prioritization for carrying out detailed GHG inventories in key source categories of GHG emissions to ensure Ukraine's participation in international activities on climate change mitigation. According to methodological guidance a key source category is one that is prioritized within the national inventory system because it is estimated to have a significant influence on a country's total GHG inventory in terms of the absolute level of emissions. These include economic sectors that account for 95% of cumulative country's GHG emissions with a 90% probability. The largest emissions source in Ukraine is the energy sector, followed by industrial processes and construction, metallurgy, natural gas and coal extraction, agriculture and solid waste.

Among methane emissions sources the SW sector is the fourth after natural gas and coal extraction and, enteric fermentation in livestock. The preliminary estimates showed that the SW sector in Ukraine generated approximately 4.3% of the total volume of ÑÎ2-equivalent emissions in 1990.

Methane (CH4) is an important greenhouse gas and a major environmental pollutant.

Methane is also the primary component of natural gas and, as such, can be a valuable energy source. Since methane is a source of energy as well as a greenhouse gas, reducing methane emissions from SWDSs is economically beneficial. Methane emission reduction strategies offer one of the most effective means of mitigating global warming in the short term for the following reasons:

Methane is one of the principal greenhouse gases, second after carbon dioxide (CO2) in its contribution to global warming. In fact, methane is responsible for 18 percent of the total contribution in 1990 of all greenhouse gases. Ìethane is a more potent greenhouse gas than CO2;

Methane concentrations in the atmosphere have risen rapidly. Atmospheric concentrations of methane have been increasing at about 0.6 percent per year and have more than doubled over the last two centuries. In contrast, CO2 atmospheric concentration is increasing at about 0.4 percent per year;

Methane has a shorter atmospheric lifetime than other greenhouse gases - methane lasts around 11 years in the atmosphere, whereas CO2 lasts about 120 years. Due to methane's high potency and short atmospheric lifetime, stabilization of methane emissions will have an immediate impact on mitigating climate change.

The unique characteristics of methane emissions make methane recovery one of the most attractive and efficient ways to mitigate climate change.

Methane is generated in SWDSs as a direct result of the natural decomposition of solid waste under anaerobic (in the absence of oxygen) conditions. The organic component of landfill waste is decomposed by bacteria in a complex biological process that produces methane, carbon dioxide, and other trace gases. It should be noted that CO2 emissions from landfills do not contribute to the increase in CO2 abundance in the atmosphere because the carbon in the CO2 is of recent biogenic origin (e.g., from crops and trees). Estimates of global methane emissions from SWDSs range from 20 to 70 millions tonnes per year, accounting for about six to twenty percent of total annual anthropogenic methane emissions.

The process of decomposition of organic matter depends on a number of factors. Microbial populations, which actually produce methane, vary significantly among landfills due to differences in conditions. Consequently, characteristics of landfills influence the generation of methane and its emission from SWDSs. The key factors that determine methane production are:

Waste composition. Methane is produced from the organic component of solid waste (e.g., food scraps, paper, and other biodegradable materials). The decomposition (fermentation) of this organic material leads to methane emissions. Therefore, high levels of organic materials in the waste increase the amount of landfill gas and the share of methane in it.

Anaerobic environment. In order to produce methane, organic material must break down in an anaerobic environment (i.e. in the absence of oxygen). Deliberate covering of solid waste with dirt in a landfill leads to the creation of anaerobic conditions. Similarly, the organic material in large open dumps becomes effectively covered by the other waste, thereby leading to anaerobic conditions and methane generation. Waste compaction also reduces the availability of oxygen, thus creating favorable conditions for methane generation.

Moisture content. Moisture is essential for anaerobic decomposition (i.e., fermentation). Water provides the medium for cell growth and metabolism, and transportation of nutrients and bacteria within the landfill.

Acidity and chemical composition of SW. Living systems are sensitive to pH (a measure of acidity) and hazardous chemicals. The optimal pH for methane production is between 6.8 and 7.2. Methane production decreases sharply with pH values below 6.5.

Temperature. Methanogenic bacteria are affected by temperature. The rate of methane production is maximized between 50° and 60°C, but can occur anywhere from between 10° to 60° C.

In addition, the refuse consistency, the landfill design and area, availability of liquid control (surface drainage, facilities to control leachate) and other specific factors can affect the quantity and rate of methane generation.