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NOVA Field Experiment

NOVA Field Site From mid-July to mid-August 1996, scientists from NOAA's Air Resources Laboratory participated in the Project NOVA (Natural emissions of Oxidant precursors: Validation of techniques and Assessment) field experiment in rural northeastern North Carolina. The primary purpose of the project was to compare different methodologies for estimating the release of nitric oxide (NO) from agricultural soils. Secondary goals of the project included the quantification of emission estimates of NO from agricultural crop land, and characterization of tropospheric photochemistry at a rural site in the southeastern U.S.

NOVA Field Site The site of the NOVA field project was a private farm near Plymouth, NC. The experiment was conducted over a field of soybeans, with an upwind fetch of 1 kilometer. Fast-response NO sensors were deployed at 3, 5, and 10 meters to provide emission flux estimates via eddy correlation. Additionally, eddy correlation flux measurements of NO2 and O3 were also conducted, by scientists at ATDD and Argonne National Laboratory (ANL). Slow-response concentration measurements of NO, NOx, and O3 were conducted by ARL to provide selective, specific measurements with which the photochemical perturbation to the NO emission flux profiles could be inferred. Scientists from ARL/ATDD deployed two eddy correlation systems (at 3 and 10 m), consisting of fast response measurements of 3-D winds and temperature (sonic anemometers); ozone (coumarin chemiluminescence); NO2 (luminol chemiluminescence), and water vapor and CO2 (IRGA). Additionally, a flux-gradient tower was erected to provide gradient measurements of temperature and water vapor concentrations, and wind speed and direction; eddy diffusivities/transfer coefficients of sensible and latent heat, and momentum were thus derived. Soil moisture and heat fluxes were also measured, as were net radiation, PAR, and UV radiation, to investigate and close the energy balance at the site.

NOVA Field Site Despite the impact of Hurricane Bertha before, and numerous heavy and prolonged precipitation events during the project, NOVA was an operational success, and most systems performed well. Only 5-6 days of in-sector winds (SW flow) were observed, making for a limited data set. However, initial observations show excellent agreement among the three eddy correlation measurements of NO, excellent agreement between static and dynamic chamber (enclosure) methods, and reasonable agreement between the micrometeorological and enclosure techniques. The three fast response NO sensors were co-located at 10 m for a side-by-side flux intercomparison at the end of the project. Nitric oxide calibration standards were cross-compared to ensure consistency of calibration. Finally, while nitrogen-fixing crops such as soybean are not generally fertilized, arrangements were made with the farmer to apply ammonium nitrate fertilizer to a portion of the field, in order to stimulate NO emission. Nitric oxide emission fluxes of up to 1 ng N m-2 s-1 were observed prior to fertilization; emission rates approximately doubled with the application of NH4NO3


  • To Compare NO Emission fluxes Derived from Micrometeorological Techniques with Those from Chamber (Enclosure) Methods.
  • To Quantify the NO Emission Flux from Agricultural Lands Representative of the Southeastern U.S.
  • To Measure Flux Profiles of NO and NO2 and to Investigate the Role of Tropospheric Photochemistry in Modifying the Surface Fluxes of NO and NO2 (Flux Divergence).
  • To Characterize the Air Quality and Tropospheric Photochemistry at a Rural Site in the Southeastern United States.
Sponsors Participants
Environmental Protection Agency,
With In-Kind Contributions from:



QA/QC Protocols

  • NIST-Traceable Calibration and Flow Measurement Standards
  • Baseline Correction and Twice-Daily Calibrations of ARL NO and NOx Sensors
  • Cross-Calibrations of All NO Calibration Standards (NOAA, NASA, UMD, NCSU)
  • Common Sonic Anemometry and NO Flux Measurements at 10 m (NOAA, DOE. UMD)

Preliminary Results -- DO NOT CITE!

  • Mid-Day NO emission fluxes from a soybean field in July-August 1996 were typically less than 1 ng N/m2 sec, and almost always less than 2 ng N/m2 sec. Emission fluxes doubled immediately after fertilization with NH4NO3 (ca. 25 Kg/Ha)
  • Under convectively unstable conditions and light winds, all 3 E/C NO flux estimates agreed well with one another
  • Enclosure (static and dynamic) measurements of NO emission flux agreed well with each other, but only sometimes agreed with micromet methods.
  • Cross calibration of NO standards revealed significant (>40%) errors in some of the calibration standards. Correcting for calibration errors significantly improved agreement.
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