Atmospheric Simulation of Time-Dependent Landfill Methane Emissions

Landfill methane emissions are difficult to estimate due to limited observations and data uncertainty. A surface flux drag law for landfill methane emissions is added to the Weather Research and Forecasting model (WRF) to predict emissions based on soil and atmospheric methane concentrations and horizontal wind speed, based on similar surface flux equations used by WRF for heat and moisture. Simulations of landfill methane emissions and the tracer dilution method used to estimate landfill methane emissions are run over different time periods for Sandtown Landfill in Delaware, USA. Two questions are explored through analysis of the simulations: how does the accuracy of the tracer dilution method change over the course of the day, and how do variations in wind speed affect the variability of landfill methane emissions on short time scales (a few hours). Models and observations show that soil methane concentration does not change significantly on small time scales, so variability in emissions over a one to two hour measurement period can be attributed to variations in wind speed. The values used for soil methane concentration in the daily cover and intermediate cover are taken from the California Landfill Methane Inventory Model (CALMIM), which is used to simulate soil processes and predict soil methane concentrations for Sandtown Landfill.