Nitrous oxide (N sub(2)O) emissions from California based on 2010 CalNex airborne measurements

• Published in: Journal of geophysical research. Atmospheres 2013-04, Vol.118 (7), p.2809-2820
• Main Authors: Xiang, Bin, Miller, Scot M, Kort, Eric A, Santoni, Gregory W, Daube, Bruce C, Commane, Roisin, Angevine, Wayne M, Ryerson, Tom B, Trainer, Michael K, Andrews, Arlyn E, Nehrkorn, Thomas, Tian, Hanqin, Wofsy, Steven C
• Format: Article
• Language: English
• Subjects: Atmospherics; Emission; Fertilizers; Inventories; Mathematical models; Nitrous oxides; Pollution sources; Stockpiling
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1002/jgrd.50189

Nitrous oxide (N sub(2)O) is an important gas for climate and for stratospheric chemistry, with a lifetime exceeding 100years. Global concentrations have increased steadily since the 18th century, apparently due to human-associated emissions, principally from the application of nitrogen fertilizers. However, quantitative studies of agricultural emissions at large spatial scales are lacking, inhibited by the difficulty of measuring small enhancements in atmospheric concentration. Here we derive regional emission rates for N sub(2)O in the agricultural heartland of California based on analysis of in-situ airborne atmospheric observations collected using a new quantum cascade laser spectrometer. The data were obtained on board the NOAA WP-3 research aircraft during the CalNex (California Research at the Nexus of Air Quality and Climate Change) program in late spring 2010. We coupled the WRF (weather research and forecasting) model, a meso-scale meteorology model, with the STILT (stochastic time-inverted Lagrangian transport) model, a Lagrangian particle dispersion model, to link our in-situ airborne observations to surface emissions. We then used a variety of statistical methods to identify source areas and to optimize emission rates. Our results are consistent with the view that fertilizer application is the largest source of N sub(2)O in the Central Valley. The spatial distribution of surface emissions, based on California land use and activity maps, was very different than indicated in the leading emission inventory (EDGAR 4.0). Our estimated total emission flux of N sub(2)O for California in May and June was 3 - 4 times larger than the annual mean given for the state by EDGAR and other inventories, indicating a strong seasonal variation. We estimated the statewide total annual emissions of N sub(2)O to be 0.042 plus or minus 0.011 Tg N/year, roughly equivalent to inventory values if we account for seasonal variations using observations obtained in the midwestern United States. This state total N sub(2)O emission is 20.5 Tg CO sub(2) equivalent (100year global warming potential=310 CO sub(2) eq/g N sub(2)O), accounting for approximately 4% of the state total greenhouse gas emissions. Key Points * Bottom-up N2O inventories have erroneous spatial information. * Agriculture is the dominant N2O source in California Central Valley. * Estimated annual state emissions are 1~2 times higher than inventory values.