The proposed work will produce robust estimates for emission rates of methane and nitrous oxide from California, spatially distributed, disaggregated by major sector or emission process, time resolved during spring and early summer, and rigorously assessed for accuracy. We will use the CalNex data set obtained by the NOAA P-3 aircraft in May and June, 2010. The principal data sets we will use are our own measurements of CO2, CO, CH4 and N2O concentrations, combined with data for CO2, CO, CH4, NOx, NOy, SO2, solvent gases, black carbon, NH4+, and other species measured by NOAA investigators on the P-3 aircraft. Our approach uses a high resolution assimilated meteorological model (WRF) with a Lagrangian Particle Dispersion Model (STILT) to produce a �??footprint�?� (transfer function between surface emission flux and concentration increment at a receptor). We overlay the footprint onto a priori surface flux fields to simulate the measured concentrations of CH4 and N2O at receptor points that cover California in space and time (the P-3 aircraft in CalNex). We will determine the optimal constraints on upwind emission rates by adjusting process-specific emissions from a priori flux inventories, focusing on those in current use by California regulators to guide planning for reductions in Greenhouse Gas emissions (EDGAR, GEIA, and California GHG Inventory, plus process-based emission models DLEM and DNDC). Geostatistical inverse analyses will also be carried out, to derive fluxes independent of a priori fluxes. The work involves close collaboration with more than a half dozen NOAA colleagues involved with CalNex.