Trace gas emissions from municipal solid waste landfills: A review.

Trace gas emissions from municipal solid waste (MSW) landfills have received increasing attention in recent years. This paper reviews literature published between 1983 and 2019, focusing on (i) the origin and fate of trace gas in MSW landfills, (ii) sampling and analytical techniques, (iii) quantitative emission measurement techniques, (iv) concentration and surface emission rates of common trace compounds at different landfill units and (v) the environmental and health concerns associated with trace gas emissions from MSW landfills. Trace gases can be produced from waste degradation, direct volatilisation of chemicals in waste products or from conversions/reactions between other compounds. Different chemical groups dominate the different waste decomposition stages. In general, organic sulphur compounds and oxygenated compounds are connected with fresh waste, while abundant hydrogen sulphide, aromatics and aliphatic hydrocarbons are usually found during the methane fermentation stage. Selection of different sampling, analytical and emission rate measurement techniques might generate different results when quantifying trace gas emission from landfills, and validation tests are needed to evaluate the reliability of current methods. The concentrations of trace gases and their surface emission rates vary largely from site to site, and fresh waste dumping areas and uncovered waste surfaces are the most important fugitive emission sources. The adverse effects of trace gas emission are not fully understood, and more emission data are required in future studies to assess quantitatively their environmental impacts as well as health risks.