REAL-TIME MAPPING OF HYDROXYLAMINE AND OTHER TRACE GASES IN SOIL

The nitrogen cycle is a foundational process in the critical zone that enables Earth's soils to sustain plant and animal life. Although many of the transformations that make up the nitrogen cycle occur in aerobic and anaerobic regions of the vadose zone, they are intimately connected to the atmosphere and biosphere.Soil is both a source and a sink of atmospheric dinitrogen (N2) as well as a source of nitrous oxide (N2O), nitric oxide (NO), and other compounds that play key roles in local air quality and global climate change.Understanding the mechanisms that drive subsurface nitrogen transformations is important for improving agricultural productivity and unraveling the contributions of natural and agricultural soil microbiomes to air pollution and climate change. Controlling the depositions, transformations, and losses of nitrogen in soil is a primary goal in efforts to maximize crop yield, reduce production costs, and minimize the environmental impact of agricultural activities.While great strides have been made toward understanding these transformations, there remain fundamental mechanistic questions that are presently difficult to address due to the heterogeneous and fluctuating nature of real-world soil environments. New, nondestructive experimental tools are needed to interrogate these processes on spatial and temporal scales that are relevant to the nitrogen cycling microbiome.The major goals of this project are to i) combine novel subsurface solute extraction with spectroscopic gas-phase detection to enable new in situ observations of key subsurface nitrogen cycling pathways with high spatial and temporal resolution; and ii) develop a commercially viable sampling and detection system based upon these technical efforts.The central concept behind this Phase II SBIR project is to couple a microdialysis-based soil water extraction methodwith a high precision infrared trace gas analyzer for detection of nitrate, nitrite, and hydroxylamine with micromolar sensitivity. Achievingthese major goals requires successful completion of the following objectives:Interfacing mL liquid sample to the TILDAS: further modifying the TILDAS absorption cell design and choosing materials to best operate with liquid samples. Phase I results suggest that the major challenge for quantitative measurement of liquid injections is analyte losses to absorption cell surfaces in the infrared gas analyzer. In Phase II, we will pursue a multi-pronged approach to limit surface losses including modifying the cell body design, heating the cell, and changing cell surfaces to limit losses.Flow design and sample preparation: designing and building the sample multiplexing system and optimizing automated sample preparation.In Phase II we will design and assemble an on-line, automated, multiplexed microdialysis (MD) flow system for integration with a TILDAS. This consists of two components: the multiplexing system and sample preparation. The multiplexing system will utilize multiselector and trapping valves to extract microliter sample volumes from microdialysis probes. Development of a commercializable hardware and software package will allow for automated, hands off sampling from an array of microdialysis probes. The sample preparation component consists of testing and automating simple chemical reaction (acidfication) steps to detect nitrate and nitrite with high sensitivity.Optimizing spectroscopy and building a TILDAS. Hydroxylamine, nitric acid and nitrous acid will be simultaneously detected with a dual-laser TILDAS instrument. One laser will be used to measure NH2OH and the second laser will measure both HNO3 and HONO. We will purchase and install both lasers at appropriate wavelengths for optimal detection of all three species and characterize spectroscopic parameters in the hydroxylamine spectral region.Given the linestrengths used in the simulation, we expect a sensitivity of~30 nM for nitrite and ~260 nM for nitrate.Testing, refining, and challenging the system.This objective will be achieved by i) assemblingthe multiplexed MD system in the laboratory, ii) optimizing operational parameters and best practices, iii) determiningmeasurement conditions under which this measurement approach is challenged, and implementing a simple calibration setup.Laboratory demonstration. This objective is aimed at demonstrating the system in a real world laboraotry environment to address and interesting scientific challenge.The microdialysis-based sampling technique will be used to expand mechanistic understanding of soil N cycling in post-fire environments and determine how novel pyrophilous or "fire-loving" microbiomes influence soil N transformations and emissions. These laboratory studies will be in collaboration with Prof. Peter Homyak at the University of California, Riverside.Commercialization.The efforts described here will allow us to develop a commerical system that will enable subsurface sampling of important nitrogen species relevant to the nitrogen cycle.The system will have substantial commercial potential due to its ability to quantify important chemical species in soil with high sensitivity and selectivity at unprecedented spatial and temporal scales. We will achieve this objective with the support of our commercialization assistance partner, Dawnbreaker.