Emission factors of fugitive methane from underground coal mines in China: Estimation and uncertainty

Fugitive methane from underground coal mining is the main source of methane emissions in China. Accurate and updateable methane emission factors for underground coal mining are of great significance for the accounting of methane emissions in China. In this paper, 10,951 underground coal mines are investigated for developing an emission factor matrix for national and provincial scales. For national emission factors, 27 types of emission factors are determined according to the classification of the ownership of the enterprise, gas emission rate, and maximum mining depth. For provincial emission factors, three types of emission factors for 25 provinces are determined based on gas emission rates. Based on these metrics, this paper uses bootstrap and Monte Carlo simulations to determine the uncertainty range of different emission factors at the 95% confidence interval (CI). The results show that emission factors at the national scale ranged from 3.005 m(3)/t to 54.487 m(3)/t, with a 95% CI of 2.735 m(3)/t to 76.082 m(3)/t, and that emission factors at the provincial scale ranged from 0.58 m(3)/t to 56.19 m(3)/t, with a 95% CI of 0.347 m(3)/t to 108.115 m(3)/t. By comparison, the emission factors calculated in this paper are more representative than the default values recommended by the Intergovernmental Panel on Climate Change (IPCC). In addition, these results are more specific and updateable than those in previous studies, which lays a foundation for the future study of fugitive methane emissions from underground coal mines at different scales.