A continuous record of atmospheric N2O measured from a tower in northern California captures strong pulses of N2O released by coastal upwelling events. The atmospheric record offers a unique, observation-based method for quantifying the coastal N2O source. A coastal upwelling model is developed and compared to the constraints imposed by the atmospheric record in the Pacific Northwest coastal region. The upwelling model is based on Ekman theory and driven by high-resolution wind and SST data and by relationships between subsurface N2O and temperature. A simplified version of the upwelling model is extended to the world's major eastern boundary regions to estimate a total coastal upwelling source of ~0.2 ¿ >70% Tg N2O-N/yr. This flux represents ~5% of the total ocean source, estimated here at ~4 Tg N2O-N/yr using traditional gas-transfer methods, and is probably largely neglected in current N2O budgets.