Methane Concentration in Fiji Air: A Study of its Emission Trends and Source Strengths

Abstract

In this study we have developed an in house capacity at the Chemistry Department, the University of the South Pacific, to analyze methane in ambient air to a precision of 1.5% using a custom converted Gas Chromatograph with FID detector. The technical support to develop this capacity was provided by our overseas partner, National Institute of Water and Atmospheric Research (NIWA). The air samples were collected from known sources of methane such as the digester at the sewage treatment plant, rubbish dump, wetlands, sugar cane burning in the western side of Viti Levu, geothermal emission in Vanua Levu, rice farms and cattle farms from September 2001 to June 2002 and were analyzed. Through inter-laboratory measurements involving NIWA a mean drift of 0.8% was obtained. The methane concentration in the ambient air has a seasonal cycle with a minimum during late January and a maximum during the July to August period. The digester at the sewage plant recorded the maximum concentration of approximately 70 ppmv followed by Lami rubbish dump with values ranging from 4.37 – 13.35 ppmv. The data from cattle farms, wetlands, rice farms and hot springs recorded emissions in the range of 2.00 – 5.11 ppmv, 1.85 – 4.25 ppmv, 1.77 – 2.62 ppmv and 2.06 – 1.90 ppmv respectively.