Seasonal variations in N₂O emissions from central California

We estimate nitrous oxide (N₂O) emissions from Central California for the period of December 2007 through November 2009 by comparing N₂O mixing ratios measured at a tall tower (Walnut Grove, WGC) with transport model predictions based on two global a priori N₂O emission models (EDGAR32 and EDGAR42). Atmospheric particle trajectories and surface footprints are computed using the Weather Research and Forecasting (WRF) and Stochastic Time-Inverted Lagrangian Transport (STILT) models. Regression analyses show that the slopes of predicted on measured N₂O from both emission models are low, suggesting that actual N₂O emissions are significantly higher than the EDGAR inventories for all seasons. Bayesian inverse analyses of regional N₂O emissions show that posterior annual N₂O emissions are larger than both EDGAR inventories by factors of 2.0 ± 0.4 (EDGAR32) and 2.1 ± 0.4 (EDGAR42) with seasonal variation ranging from 1.6 ± 0.3 to 2.5 ± 0.4 for an influence region of Central California within approximately 150 km of the tower. These results suggest that if the spatial distribution of N₂O emissions in California follows the EDGAR emission models, then actual emissions are 2.7 ± 0.5 times greater than the current California emission inventory, and total N₂O emissions account for 8.1 ± 1.4% of total greenhouse gas emissions from California.