Spatial variations of atmospheric methane concentrations in China

Methane (CH4) is regarded as one of the most important greenhouse gases due to its radiative forcing. Therefore, in running climate models, it is important to have accurate estimates of CH4 concentrations at an appropriate scale. Although great efforts have recently been undertaken to quantify atmospheric CH4 concentrations based on extensive ground-based measurements, it is still difficult to obtain the spatial variations of the CH4 volume mixing ratio (VMR) on a regional scale. This study analyses the spatial variations of CH4 VMRs in China, based on the retrieved CH4 data from Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) spectra. The results showed that the spatial distribution of CH4 VMRs presented decreasing gradients from south-east to north-east and the lowest CH4 concentrations were located on the Qinghai-Tibet Plateau. Paddy fields were the main sources of CH4 in China, as shown through spatial analysis. Natural wetlands and population also contributed to CH4 VMRs. Plant, climate and soil properties presented a strong positive influence on CH4 concentrations, which could be used to interpret the spatial variations. Stepwise multiple regression modelling results showed that temperature, normalized difference vegetation index (NDVI) and soil total nitrogen could explain 76.9% of the differences in CH4 throughout China, and the average difference between the retrieved and the modelled methane concentrations was 14 ppb.