Methane Emissions in Melbourne, Australia; Part 1: Prior Estimates Using Global and National Data

Abstract This paper is the first part of a comprehensive study that enhances the understanding of methane emissions in Melbourne, Australia, by combining emission inventories and atmospheric observations. We utilized global, national and regional datasets to produce prior gridded estimates of methane emissions for the Melbourne region. We ran an atmospheric transport model with these prior emissions and boundary conditions from the Whole Atmosphere Community Climate Model (WACCM), and compared the calculated mole fractions with observations at five stations during January to June 2023. Our comparisons revealed a mismatch in the boundary conditions from WACCM and the long‐term national baseline data. We adjusted the boundary condition information using long‐term in situ observations, which significantly reduced a nearly 50 ppb offset in the global boundary condition data. Our results indicate that the model driven by prior emission estimates reproduces the observed temporal variability of atmospheric methane reasonably well, but systematically underestimates mole fraction magnitudes. We see biases for each month and site of approximately 20–196 ppb without data selection, reducing to about 5–52 ppb when nighttime low wind‐speed data are excluded. This suggests that the prior methane emissions are underestimated in the Melbourne region.