Seasonally resolved excess urban methane emissions from the Baltimore/Washington, DC metropolitan region

Urban areas are increasingly recognized as an important source of methane (CH4), but we have limited seasonally resolved observations of these regions. In this study, we quantify seasonal and annual urban CH4 emissions over the Baltimore, Maryland and Washington, DC metropolitan regions. We use CH4 atmospheric observations from four tall tower stations and a Lagrangian Particle Dispersion Model to simulate CH4 concentrations at these stations. We directly compare these simulations with observations, and use a geostatistical inversion method to determine optimal emissions to match our observations. We use observations spanning four seasons and employ an ensemble approach considering multiple meteorological representations, emission inventories, and upwind CH4 values. Forward simulations in winter, spring and fall underestimate observed atmospheric CH4 while in summer simulations overestimate observations due to excess modeled wetland emissions. With ensemble geostatistical inversions, the optimized annual ...