Spatiotemporal Variations in Atmospheric CH4 Concentrations and Enhancements in Northern China Based on a Comprehensive Dataset: Ground-based Observations, TROPOMI Data, Inventory Data and Inversions

Abstract. Methane (CH4) is a potent greenhouse gas with a global warming potential that is 28–36-fold higher than that of CO2 at the 100-year scale. Northern China notably contributes to CH4 emissions. However, high uncertainties remain in emissions, and observation gaps exist in this region, especially in urban areas. Here, we compiled a comprehensive dataset (available at https://doi.org/10.5281/zenodo.10957950) (Han et al., 2024), including ground- and satellite-based observations, inventory data and modeling results, to study the CH4 concentration, enhancement and spatiotemporal variation in this area. High-precision in situ observations from Beijing and Xianghe revealed that obvious seasonal cycles and notable enhancements (500–1500 ppb) occurred at a regional background site (Shangdianzi). We found significant increasing trends in the CH4 concentration over time in both the ground- and satellite-based observations and positive correlations between these observations. Anthropogenic emissions largely contributed to surface concentration variations and their increases in middle and southern Shanxi Province and northern Hebei Province. However, a spatially inconsistent pattern was observed between the results of optimized simulations driven by surface atmospheric inversion data and Tropospheric Monitoring Instrument (TROPOMI) column CH4 observations in summer. Further validation on the basis of this comprehensive dataset indicated that the TROPOMI data may exhibit systematic bias in summer. The posterior concentrations generally agreed well with the surface in situ observations (mean biases ranging from -2.3~80.7 ppb). The posterior surface CH4 concentrations (with a spatial resolution of 0.5°× 0.625°) revealed that southern Shanxi, northern Henan, and Beijing exhibited relatively high levels (an increase of ~300 ppb), which were positively correlated with the PKU-CH4-v2 emission inventory data. This study provides a comprehensive dataset of CH4 concentrations and enhancements in high-emission areas, which can benefit the research community and policy-makers for designing future observations, conducting atmospheric inversions and formulating policies.