Seasonal Variations in CH4 Emissions from Central California

Methane emissions constitute an uncertain yet likely significant fraction of California’s greenhouse gas emissions burden. Here, we determine CH4 emissions from Central California using tower measurements, and an inverse model approach combining Weather Research and Forecast meteorology (WRF) predictions with the stochastic timer-inverted Lagrangian transport (STILT) model (henceforth WRF-STILT). We evaluate transport model errors due to uncertaintiesy in planetary boundary layer (PBL) and wind velocities by comparing model predictions with PBL heights and wind velocities determined from a radar wind profiler near located near (within 8 km) of the primary tower site (38.26o,-121.49o). Comparing PBL heights from two different boundary layer schemes in WRF-STILT (the Eta (TKE) scheme and the Penn State (PSU) scheme using a Richardson number approach), we found that the TKE scheme more accurately captures the seasonal variations in PBL height at the Sacramento River Delta. Incorporating the error analysis results, we report initial estimates of seasonal variations in CH4 emissions from either source sectors (e.g., livestock, natural gas infrastructure, landfills, etc.) or total emissions from distinct spatial sub-regions in Central California.