Nitrous Oxide (N2O) Emissions from California based on 2010 CalNex Airborne Measurements

Author: B. Xiang and Thomas Nehrkorn
December 7, 2012
Poster presentation
AgU Fall Meeting 2012

Bin Xiang; Scot Miller; Eric A. Kort; Gregory W. Santoni; Bruce Daube; Roisin Commane; Wayne M. Angevine; Thomas B. Ryerson; Michael Trainer; Arlyn E. Andrews; Thomas Nehrkorn; Hanqin Tian; Steven C. Wofsy (2012) Nitrous Oxide (N2O) Emissions from California based on 2010 CalNex Airborne Measurements. AGU Fall Meeting 2012, San Francisco, CA.

Nitrous oxide (N2O) is an important gas for climate and for stratospheric chemistry, with an atmospheric lifetime exceeding 100 years. Global concentrations have increased steadily since the 18th century, apparently due to human-associated emissions, principally from application of nitrogen fertilizers. However, quantitative studies of agricultural emissions at large spatial scales are lacking, inhibited by the difficulty of measuring small enhancements of atmospheric concentrations. Here we derive regional emission rates for N2O in the Central Valley of California, based on analysis of in-situ airborne atmospheric observations collected using a quantum cascade laser spectrometer. The data were obtained on board the NOAA P-3 research aircraft during the CalNex (California Research at the Nexus of Air Quality and Climate Change) program in May and June, 2010. We coupled WRF (Weather Research and Forecasting) model to STILT (Stochastic Time-Inverted Lagrangian Transport) to link our in-situ observations to surface emissions, and then used a variety of statistical methods to identify source areas and to extract optimized emission rates from the inversion. Our results support the view that fertilizer application is the largest source of N2O in the Central Valley. But the spatial distribution of derived surface emissions, based on California land use and activity maps, was very different than indicated in the leading emissions inventory (EDGAR 4.0), and our estimated total emission flux of N2O for California during the study period was 3 - 4 times larger than EDGAR and other inventories.