As a result, a part of the measurement path is not perpendicular but parallel to the plume axis. Variations in wind direction have a more pronounced effect on the concentrations on this part of the path which caused the variation in the subsequent emission estimates. The emission levels in 1999 were significantly higher than obtained in 1997 and 1998. Also the main source area on the landfill changed from the south east to the middle on the south side compared to the previous years. The air pressure showed a minimum of 1000 mbar the day before measurements.
Low temperatures inhibit methane oxidation activity in the topsoil of the landfill.