Estimates of methane emissions in Beijing using a backward trajectory inversion model

Abstract

From July to December 2000, ambient methane concentrations were continuously monitored at one sampling site 92 m above ground in Beijing city. Together with meteorological data measured at 22 municipal stations, a backward trajectory inversion model was developed to calculate methane emissions in the city. Model results were compared with a methane emission inventory established with updated emission factors and intensive survey of sources.

From the source inventory, the total methane emissions were estimated to be 296.4Gg/yr, while municipal solid waste and fossil fuel account for 54.5% and 32.4% of total emissions. This showed that methane emissions in Beijing were dominated by anthropogenic sources. The inversion model described real-time methane emitted into the mixing layer along a backward trajectory path and also the exchange between reservoir layer and mixing layer. The Singular Value Decomposition (SVD) matrix inversion technique was used to calculate the methane emissions in each grid in the simulated region. The source distribution and quantitative results from model agreed well with the emission inventory, and the largest uncertainty in it was the distribution of methane emission from coal mines due to lack of trajectories covering coal mine areas.