Nitrous-Net: An Experimental and Modelling Approach To Constrain Nitrogen Emission From Agriculture

Abstract:

Researchers from Mesa Photonics, LLC, George Washington University (GWU), Washington College (WC), and the University of Minnesota Twin Cities (UM) are proposing a remote sensing method to inform N₂O flux determination from large scale agricultural actives, including intensive bio-crop production. Ground based remote sensors will be combined into a network called Nitrous-Net. Sensor nodes will be deployed at 1 to 15-km spacing with each sensor covering between 1,000 and 40,000 hectares. The sensors measure gas concentration profiles that, when combined with meteorological data, are converted to fluxes.

The approach builds on recent success by the Mesa Photonics and GWU team members for remote sensing of CO₂, CH₄, and water vapor, and on work by Tsai et al on N₂O sensing, both using a variant of Laser Heterodyne Radiometry (LHR). LHR provides concentration measurements similar to those obtained from airborne platforms including satellites at a fraction of the cost and with much higher duty factors.

To test this approach two or more LHR vertical profiling systems will be built and deployed to help constrain “farm-scale” N₂O emissions. We plan to test our experimental and modeling approach at Washington College’s River and Field Campus with validation from an array of flux chambers. In this approach, we will combine LHR measurements with the Weather Research and Forecasting Chemistry (WRF-Chem) model to constrain N₂O emissions using boundary layer budget and inverse modeling. The N₂O concentration profiles will provide a rich dataset with detailed behavior of N₂O temporal dynamics in the lower planetary boundary layer and will also provide information about the slowly evolving “background” N₂O concentration in the free atmosphere (i.e. above the planetary boundary layer). This information, with other “background” estimates of N₂O from NOAA sites, can be used to calculate the enhancement of N2O concentrations within the air column of the experimental and modeling domain and can provide a powerful constraint on the farm-scale N₂O flux.