Aircraft Observations of Nitrous Oxide (N2O) Wintertime Spatiotemporal Vertical Variability in the San Joaquin Valley of California

Nitrous oxide (N2O) is a long-lived and highly potent greenhouse gas that also destroys stratospheric ozone. N2O sources are uncertain, with documented differences between bottom-up and top-down emission estimates. We present a unique N2O dataset that captures the spatial and temporal variability in N2O in the atmospheric boundary layer (ABL) in the San Joaquin Valley (SJV) of California during wintertime. N2O measurements were collected as part of the NASA DISCOVER-AQ (Deriving Information on Surface Conditions from COlumn and VERtically Resolved Observations Relevant to Air Quality) campaign SJV-deployment (January–February, 2013), during which the NASA P-3 aircraft sampled more than 60 N2O vertical profiles over agricultural, urban, and rural source areas. We describe the influence of diurnal ABL dynamics and source proximity on N2O spatiotemporal vertical variability at multiple SJV locations. To infer N2O source type, we investigate enhancement ratios of N2O, methane, ammonia, carbon dioxide, and carbon monoxide separately within the nocturnal boundary, residual, and convective boundary layers, which show dairy/livestock operations are the primary wintertime N2O source. We use a nocturnal boundary layer budgeting model, constrained with aircraft vertical profiles, to estimate N2O emission rates of 60–860 mg N2O-N ha–1 h–1 across the SJV.