Devices and systems for collecting and measuring subsurface soil gases

Abstract

Provided herein are devices and systems that can be used to measure subsurface gas concentrations in order to inform users about the soil health. Also provided herein are methods of using these devices and systems to measure the subsurface concentration of one or more gases present in the soil.

Description

[0001] DEVICES AND SYSTEMS FOR COLLECTING AND MEASURING SUBSURFACE SOIL GASES

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims benefit of U.S. Provisional Application No. 63 / 569,476, filed March 25, 2024, which is incorporated herein by reference in its entirety.

[0004] BACKGROUND

[0005] The plant rhizosphere contains billions of microorganisms per gram of soil. In many cases, these microorganisms are either beneficial or neutral to plant growth. A number of microorganisms are known to be present in soil ecological niche (rhizosphere) having beneficial effects on plant growth. These beneficial plant growth promoting properties can include nitrogen fixation, iron chelation, phosphate solubilization, and the inhibition of non-beneficial or harmful microorganisms. Some microorganisms can also improve the resistance to pests and / or can decompose plant material in soil to increase soil organic matter. During these processes, microorganisms can emit gases that are characteristic of ongoing biochemical processes within the soil. Likewise, geochemical processes can drive the evolution of gases within the soil

[0006] Soil health in agricultural settings could potentially benefit from a greater understanding of gas concentrations present within the soil over time, including the concentration of gases emitted and / or absorbed by bacteria and the concentration of gases generated or consumed by other processes (e.g., geochemical processes. In particular, a detailed understanding of such gas concentrations could improve management decisions and agricultural production. However, to allow for such advances, improved systems for characterizing gas concentrations within the soil are needed.

[0007] SUMMARY

[0008] Described herein are devices and systems that can be used to measure subsurface gas concentrations in order to inform users about the soil health.

[0009] For example, provided herein are gas measurement systems for measuring gas emissions from soil. These systems can comprise (a) a subsurface gas sampler positionable within the soil; and (b) a sensor assembly interfacing with the subsurface gas sampler. The subsurface gas sampler can comprise (i) a sampler housing at least partially defining a sampling chamber; (ii) one or more inlets for receiving gas emissions from soil into the sampling chamber; and (iii) a sampler outlet. The sensor assembly can comprise (i) a gas sensor unit for measuring a concentration of one or more gases within a gas sample; (ii) a sensor housing enclosing the gas sensor and comprising a sampler port coupled to the sampler outlet of the subsurface gas sampler; (iii) a sample inlet fluidly connecting the sampling chamber to the gas sensor unit; (iv) an ambient air inlet fluidly connected to the gas sensor unit via an ambient air control element, wherein the ambient air control element is configured to direct and control a flow of ambient air from a position external to the sensor housing to the gas sensor unit; and (v) a control unit operatively connected to the gas sensor unit and adapted to receive and store measurements from the gas sensor unit.

[0010] In some embodiments, the subsurface gas sampler further comprises a sample release valve controlling flow of gas emissions from the sampling chamber to the sample inlet when the sensor assembly is connected to the subsurface gas sampler. In some embodiments, the sample release valve can be actuatable between a first position where gas emissions present in the sampling chamber cannot flow from the sampling chamber to a second position wherein gas emissions present in the sampling chamber can flow from the sampling chamber.

[0011] In some embodiments, the control unit is operatively connected to the sample release valve such that the control unit directs actuation of the sample release valve between the first position and the second position. In certain embodiments, the control unit is wirelessly connected to the sample release valve.

[0012] In some embodiments, the subsurface gas sampler further comprises one or more inlet controls configured to control flow of gas emissions from the soil through the one or more inlets and into the sampling chamber. In some embodiments, the one or more inlet controls are actuatable between a first position where the one or more inlets are sealed and a second position wherein the one or more inlets are open and gas emissions can pass from soil into sampling chamber. For example, in some embodiments, the one or more inlet controls comprise a rotatable member that rotatably actuates between the first position and the second position. In some embodiments, the control unit is operatively connected to the one or more inlet controls such that the control unit directs actuation of the one or more inlet controls between the first position and the second position. In some embodiments, the control unit is wirelessly connected to the one or more inlet controls. In some embodiments, the one or more inlets selectively permit passage of gas emissions from soil while excluding water and soil from entering the sampling chamber. In certain embodiments, the one or more inlets comprise a membrane that permits transmembrane permeation of gas emissions from soil while excluding water and soil. In some embodiments, the membrane comprises a selectively permeable membrane.

[0013] In some embodiments, the one or more inlets are circumferentially disposed about the sampler housing.

[0014] In some embodiments, the sampler housing has a length, and wherein the one or more inlets comprise a plurality of inlets disposed at varying points along the length of the sampler housing.

[0015] In some embodiments, the one or more inlets comprise a plurality of inlets disposed at regular intervals along the length of the sampler housing. In certain embodiments, the regular intervals correspond to defined depths beneath the soil when the subsurface gas sampler is positioned within the soil. In some embodiments, the defined depths range from 2 cm to 60 cm beneath the soil when the subsurface gas sampler is positioned within the soil.

[0016] In some embodiments, the subsurface gas sampler further comprises one or more inlet controls configured to control flow of gas emissions from the soil through the one or more inlets and into the sampling chamber. In some embodiments, the one or more inlet controls are configured to allow a user to selectively control flow of gas emissions from the soil through selected inlets disposed at varying points along the length of the sampler housing.

[0017] In some embodiments, the one or more inlets comprise a plurality of inlets disposed at regular intervals along the length of the sampler housing. In certain embodiments, the regular intervals comprise every centimeter, every 2 cm, every 3 cm, every 4 cm, every 5 cm, every 6 cm, every 7 cm, every 8 cm, every 9 cm, or every 10 cm along the length of the sampler housing.

[0018] In some embodiments, the sampler housing has a length of from 5 cm to 75 cm. In some embodiments, the sampler housing has a diameter of from 5 cm to 50 cm, such as from 15 cm to 25 cm.

[0019] In some embodiments, the subsurface gas sampler further comprises a mesh or screen operatively coupled to the one or more inlets to prevent soil intrusion into inlets.

[0020] In some embodiments, the subsurface gas sampler further comprises a drain to remove accumulating water from sampling chamber. In some embodiments, the control unit is operatively connected to the drain to allow for opening and closing of the drain. In some embodiments, the system further comprises a pump to direct gas from the sampling chamber through the sample inlet and to the gas sensor unit. In some embodiments, the control unit is operatively connected to the pump.

[0021] In some embodiments, the subsurface gas sampler terminates at a distal end, and wherein the distal end is tapered, hardened, or a combination thereof to facilitate placement in the soil.

[0022] The gas sensor unit can comprise a nitrous oxide sensor, a NOx sensor, a CO2 sensor, a water sensor, a methane sensor, an ammonia sensor, or any combination thereof. In certain embodiments, the gas sensor unit comprises a nitrous oxide sensor and a NOx sensor.

[0023] In some embodiments, the NOx sensor comprises a base substrate; and a plurality of potentiometric sensor units connected in series and coupled to the base substrate. Each potentiometric sensor unit can comprise an electrolyte layer disposed on the base substrate; a two-part sensing electrode comprising a layer of tungsten oxide (WO3) disposed on a platinum (Pt) contact; and a reference electrode comprising platinum (Pt).

[0024] In some embodiments, the reference electrode comprises Pt-loaded zeolite Y (Pt-Y).

[0025] In some embodiments, the NOx sensor has a limit of detection of from 5 ppb to 5 ppm (e.g., from 5-100 ppb). In certain embodiments, the NOx sensor has a limit of detection of 50 ppb or less. In some embodiments, the NOx sensor has an upper limit of detection of greater than 1 ppm, such as an upper limit of detection of about 5 ppm or 10 ppm.

[0026] In some embodiments, the system further comprises a heater operatively coupled to the NOx sensor. In some embodiments, the heater is configured to heat the NOx sensor to a temperature of from 250°C to 500°C.

[0027] In some embodiments, the system further comprises a NOx scrubber for removing NO from a gas sample prior to a gas sample entering the NOx sensor. In certain embodiments, the NOx scrubber comprises KMnO-i.

[0028] In some embodiments, the nitrous oxide sensor comprises an NDIR sensor. In some embodiments, the nitrous oxide sensor has a limit of detection of 500 ppb or less. In certain embodiments, the nitrous oxide sensor has a limit of detection of from 100-500 ppb. In some embodiments, the nitrous oxide sensor has an upper limit of detection of greater than 1 ppm, such as an upper limit of detection of about 5 ppm or 10 ppm.

[0029] In some embodiments, the system further comprises a soda lime filter for removing CO2 from a gas sample prior to a gas sample entering the nitrous oxide sensor.

[0030] In some embodiments, the nitrous oxide sensor and the NOx sensor are fluidly connected in parallel. In some embodiments, the system further comprises a temperature control unit configured to regulate a temperature of the gas sample. In certain embodiments, the temperature control unit is configured to regulate the temperature of the gas sample at a temperature of from 15 °C to 40°C.

[0031] In some embodiments, the sample inlet further comprises a humidity control element. In certain embodiments, the humidity control element comprises a length of Nation tubing.

[0032] In some embodiments, the system further comprises a GPS unit. In some embodiments, the GPS unit is present in the subsurface gas sampler. In certain embodiments, the GPS reports a location of the subsurface gas sampler to the controller. In some embodiments, the GPS unit is present in the sensor assembly. In certain embodiments, the GPS reports a position to the controller.

[0033] In some embodiments, the sensor assembly is detatchably connectable to the subsurface gas sampler. In certain embodiments, the sampler port is detatchably connectable the sampler outlet of the subsurface gas sampler. In some embodiments, the sample inlet fluidly connects the sampling chamber to the gas sensor unit when the sensor assembly is connected to the subsurface gas sampler.

[0034] Also provided herein are gas measurement systems for measuring gas emissions from soil that comprise (a) a subsurface gas sampler positionable within the soil; and (b) a sensor assembly detatchably connectable to the subsurface gas sampler. The subsurface gas sampler can comprise

[0035] (i) a sampler housing at least partially defining a sampling chamber; (ii) one or more inlets for receiving gas emissions from soil into the sampling chamber; and (iii) a sampler outlet. The sensor assembly can comprise (i) a gas sensor unit for measuring a concentration of one or more gases within a gas sample; (ii) a sensor housing enclosing the gas sensor and comprising a sampler port detatchably connectable the sampler outlet of the subsurface gas sampler; (iii) a sample inlet fluidly connecting the sampling chamber to the gas sensor unit when the sensor assembly is connected to the subsurface gas sampler; (iv) an ambient air inlet fluidly connected to the gas sensor unit via an ambient air control element, wherein the ambient air control element is configured to direct and control a flow of ambient air from a position external to the sensor housing to the gas sensor unit; and (v) a control unit operatively connected to the gas sensor unit and adapted to receive and store measurements from the gas sensor unit.

[0036] Also provided herein are gas measurement systems for measuring gas emissions from soil that comprise (a) a subsurface gas sampler positionable within the soil; and (b) a sensor assembly interfacing with the subsurface gas sampler. The subsurface gas sampler can comprise (i) a sampler housing at least partially defining a sampling chamber; (ii) one or more inlets for receiving gas emissions from soil into the sampling chamber, wherein the one or more inlets selectively permit passage of gas emissions from soil while excluding water and soil from entering the sampling chamber; and (iii) a sampler outlet. The sensor assembly can comprise (i) a gas sensor unit for measuring a concentration of one or more gases within a gas sample; (ii) a sensor housing enclosing the gas sensor and comprising a sampler port coupled to the sampler outlet of the subsurface gas sampler; (iii) a sample inlet fluidly connecting the sampling chamber to the gas sensor unit; (iv) an ambient air inlet fluidly connected to the gas sensor unit via an ambient air control element, wherein the ambient air control element is configured to direct and control a flow of ambient air from a position external to the sensor housing to the gas sensor unit; and (v) a control unit operatively connected to the gas sensor unit and adapted to receive and store measurements from the gas sensor unit.

[0037] In some embodiments, the methods described herein are used to measure a subsurface concentration of a gas (or gases) present in the soil. In some embodiments, the methods can comprise making two or more measurements within a 24-hour time period (e.g., to evaluate changes in gas concentration in real time).

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1. Schematic illustration of example pathways that evolve and / or consume gas in the soil.

[0040] Figure 2 shows a perspective view of an example system described herein.

[0041] Figure 3 shows a side view of an example system described herein. Figure 4 shows a side view of an example system described herein. Figure 5 shows a side view of an example system described herein. Figure 6 shows a top view of an example system described herein. Figure 7 shows a bottom view of an example system described herein. Figure 8 shows a cutaway side view of an example system described herein. Figure 9 shows a cutaway perspective view of an example system described herein. Figure 10 shows a cutaway top view of an example system described herein.

[0042] Figure 11 shows an exploded view of an example system described herein, illustrating elements of the gas sensor present in the sensor assembly.

[0043] Figure 12 is a photograph illustrating a working prototype of a system described herein. Figure 13 is a photograph illustrating a working prototype of a system described herein.

[0044] Figure 14 shows a side view of an example system described herein.

[0045] Figure 15 is a schematic illustrating electrical connections present within the sensor assembly.

[0046] Figure 16 is a schematic illustrating gas flow through the systems described herein.

[0047] Figure 17 is a photograph illustrating the interior of the sensor assembly.

[0048] Figure 18 is a schematic illustration of an example nitrous oxide sensor.

[0049] Figure 19 is an example of the response of the example nitrous oxide sensor.

[0050] Figure 20 is a schematic illustration of an example NOx sensor.

[0051] Figure 21 is an example of the response of the example NOx sensor.

[0052] Figure 22 is a photograph showing an example NOx sensor module including a NOx sensor and NOx scrubber (catalytic filter).

[0053] DETAILED DESCRIPTION

[0054] Before the present methods and systems are disclosed and described, it is to be understood that the methods and systems are not limited to specific synthetic methods, specific components, or to particular compositions. It is also to be understood that the terminology used in this entire application is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0055] As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, to “about” another particular value, or from “about” one value to “about” another value. When such a range is expressed, another embodiment includes from the one particular value, to the other particular value, or from the one particular value to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0056] “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0057] Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises,” means “including but not limited to,” and is not intended to exclude, for example, other additives, components, integers or steps. “Exemplary” means “an example of’ and is not intended to convey an indication of a preferred or ideal embodiment. “Such as” is not used in a restrictive sense, but for explanatory purposes.

[0058] Described herein are devices and systems that can be used to measure subsurface gas concentrations in order to inform users about the soil health. Prototypes havebeen prepared using additive manufacturing. The system can include a soil subsurface gas collection chamber and a housing compartment for locating sensors and electronica. These systems can beused to measure subsurface nitrogen oxide concentrations emanating below the soil surface. Nitrogen oxides in this context include nitrous oxide (N2O) and nitric oxide and nitrogen dioxide (NO+NO2). The system can also accommodate other greenhouse gas sensors including methane (CH4) and CO2.

[0059] The systems can include an uppermost housing chamber that rests on top of the soil surface and houses sensors, batteries, and electronic components. This uppermost housing chamber can be attached to an in-ground probe chamber that is perforated and capable of penetrating into the soil surface at depths of up to, for example, 60 cm. The subsurface probe can allow for the collection of gases at depth within the soil profile. The system can have additional capability to assess differences in emissions between above and below-ground soil environments.

[0060] The system can include an electrochemical NOx solid-state sensor that has been demonstrated in the laboratory to measure NOx in the ppb-to-ppm range. The system can also include an optical N2O sensor. These sensors are placed inside the top chamber to make ppb-ppm concentrations of NOx and N2O without interferences from other gases. The system with the sensor packaging is demonstrating the potential to make in-field measurements.

[0061] Figures 2-17 provide detailed drawings of example systems and devices described herein. These example systems were manufactured using additive manufacturing techniques (3D printing) and have two compartments, a subsurface gas sampler and a housing for sensors and electronics. The subsurface gas sampler penetrates into the soil, and gases diffuse through the porous structure to the top chamber, which has the sensors and measurement electronics. In our first realization of the functioning of the device, we are focusing on N2O and NOX(NO+NO2).

[0062] In some embodiments, a partition is situated between the uppermost housing chamber and the in-ground probe chamber. This partition serves can offer flexibility to be opened or closed at will. Activation is achieved through a user-friendly switch mechanism, allowing for the isolation of the in-ground probe from the uppermost housing chamber and the sub-surface soil environment when needed. Conversely, by engaging another switch, one gains access to measure gas concentrations within the in-ground probe chamber or in the ambient above-ground surroundings.

[0063] The remarkable capability to seamlessly toggle this partition opens up exciting avenues for simultaneous and precise measurements of both subsurface soil emissions and ambient gas conditions, either through active gas sampling aided by micro-pumps or by passive diffusionbased methods. To facilitate this, micro-pumps are effectively employed to transport gases through the NOx and N2O microsensor module. In addition, the in-ground system harmonizes effortlessly with chambers equipped for venting and refreshing, enabling the tracking of emission flux changes over time.

[0064] In some embodiments, the system can allow for sampling of both the ambient and the gases generated from within the soil.

[0065] In some embodiments, the system can include a mechanism to shut off gases percolating from the soil into the probe, while measuring the collected gas within the probe.

[0066] In some embodiments, the subsurface gas sampler can be detatchable from the sensor assembly.

[0067] In some embodiments, the subsurface gas sampler can include a mechanism (e.g., a screen or mesh) to reduce or prevent the unwanted migration of soil particles into the subsurface gas sampler.

[0068] Referring now to Figures 2-17, provided herein are gas measurement systems (100) for measuring gas emissions from soil. These systems can comprise (a) a subsurface gas sampler (102) positionable within the soil; and (b) a sensor assembly (104) interfacing with the subsurface gas sampler.

[0069] The subsurface gas sampler (102) can comprise (i) a sampler housing (106) at least partially defining a sampling chamber (108); (ii) one or more inlets (110) for receiving gas emissions from soil into the sampling chamber (108); and (iii) a sampler outlet (112).

[0070] The sensor assembly (104) can comprise (i) a gas sensor unit (114) for measuring a concentration of one or more gases within a gas sample; (ii) a sensor housing (116) enclosing the gas sensor unit and comprising a sampler port (118) coupled to (or couplable to) the sampler outlet (112) of the subsurface gas sampler; (iii) a sample inlet (120) fluidly connecting the sampling chamber (108) to the gas sensor unit (114); (iv) an ambient air inlet (122) fluidly connected to the gas sensor unit (114) via an ambient air control element (124),; and (v) a control unit (126) operatively connected to the gas sensor unit (114) and adapted to receive and store measurements from the gas sensor unit.

[0071] In some embodiments, the subsurface gas sampler (102) and / or the sensor assembly (104) further comprises a sample release valve (128). Depending upon system design, the sample release valve can be incorporated in the subsurface gas sampler (102) and / or the sensor assembly (104). In the example embodiment illustrated in Figure 8, the release valve is present within the sensor assembly (104) (attached to the end of sample inlet (120) which extends into the sampling chamber (108). In other cases, the release valve can be present within the subsurface gas sampler (102), where is seals the sampling chamber (108) and mates with the sample inlet (120) present within the sensor assembly (104). In some detachable systems (e.g., where the subsurface gas sampler (102) and the sensor assembly (104) detachable), release valves can be incorporated in both the subsurface gas sampler (102) and the sensor assembly (104). The sample release valve can be operatively positioned to control the flow of gas emissions from the sampling chamber (108) to the sample inlet (120) when the sensor assembly is connected to the subsurface gas sampler. In some embodiments, the sample release valve can be actuatable between a first position where gas emissions present in the sampling chamber cannot flow from the sampling chamber to a second position wherein gas emissions present in the sampling chamber can flow from the sampling chamber.

[0072] In some embodiments, the control unit (126) is operatively connected to the sample release valve such that the control unit directs actuation of the sample release valve between the first position and the second position. In certain embodiments, the control unit is wirelessly connected to the sample release valve.

[0073] The inlets can have varying dimensions. In some embodiments, the inlets can comprise roughly circular or circular openings. In some embodiments, the inlets can have diameters of from 0.5 mm to 2 mm.

[0074] In some embodiments, the subsurface gas sampler can comprise a plurality of inlets (e.g., 5 or more, 10 or more, 20 or more, 25 or more, 50 or more, 75 or more, or 100 or more). In some examples, the subsurface gas sampler can comprise from 5 to 250 inlets (e.g., from 5 to 200 inlets, from 5 to 150 inlets, from 5 to 100 inlets, from 25 to 200 inlets, from 25 to 150 inlets, from 25 to 100 inlets, from 50 to 200 inlets, from 50 to 150 inlets, from 50 to 100 inlets, or from 75 to 200 inlets, from 75 to 150 inlets, from 75 to 100 inlets). In some examples, the plurality of inlets have a total surface area of from 100 mm2to 1000 mm2(e.g., from 250 mm2to 750 mm2). In some embodiments, the subsurface gas sampler further comprises one or more inlet controls ( 130) configured to control flow of gas emissions from the soil through the one or more inlets (110) and into the sampling chamber (108). In some embodiments, the one or more inlet controls are actuatable between a first position where the one or more inlets are sealed and a second position wherein the one or more inlets are open and gas emissions can pass from soil into sampling chamber.

[0075] For example, in some embodiments, the one or more inlet controls (130) can comprise a rotatable member that rotatably actuates between the first position and the second position. The rotatable member can comprise a sleeve that includes pores that can are sized to overlap the inlets. As the rotatable member actuates, the rotatable member can move from a first position in which the pores are registered with the inlets (allowing gas to pass) to a second position where registration is broken, such that the sleeve seals the inlets (preventing gas flow through the inlets). In some embodiments, the control unit is operatively connected to the one or more inlet controls such that the control unit directs actuation of the one or more inlet controls between the first position and the second position. In some embodiments, the control unit is wirelessly connected to the one or more inlet controls.

[0076] In some embodiments, the one or more inlets selectively permit passage of gas emissions from soil while excluding water and soil from entering the sampling chamber. In certain embodiments, the one or more inlets comprise a membrane that permits transmembrane permeation of gas emissions from soil while excluding water and soil. In some embodiments, the membrane comprises a selectively permeable membrane (e.g., a polymeric membrane that is selectively permeable to one or more of nitrous oxide, NOx, CO2, water, methane, ammonia, oxygen, or any combination thereof).

[0077] In some embodiments, the one or more inlets are circumferentially disposed about the sampler housing.

[0078] In some embodiments, the sampler housing has a length (132), and the one or more inlets comprise a plurality of inlets disposed at varying points along the length of the sampler housing. In some embodiments, the one or more inlets comprise a plurality of inlets disposed at regular intervals along the length of the sampler housing. In certain embodiments, the regular intervals correspond to defined depths beneath the soil when the subsurface gas sampler is positioned within the soil. In some embodiments, the defined depths range from 2 cm to 60 cm beneath the soil when the subsurface gas sampler is positioned within the soil. As discussed above, in some embodiments, the subsurface gas sampler further comprises one or more inlet controls (132) configured to control flow of gas emissions from the soil through the one or more inlets and into the sampling chamber. In some embodiments, the one or more inlet controls are configured to allow a user to selectively control flow of gas emissions from the soil through selected inlets disposed at varying points along the length of the sampler housing.

[0079] In some embodiments, the one or more inlets comprise a plurality of inlets disposed at regular intervals along the length of the sampler housing. In certain embodiments, the regular intervals comprise every centimeter, every 2 cm, every 3 cm, every 4 cm, every 5 cm, every 6 cm, every 7 cm, every 8 cm, every 9 cm, or every 10 cm along the length of the sampler housing.

[0080] In some embodiments, the sampler housing has a length (132) of from 5 cm to 75 cm. In some embodiments, the sampler housing has a diameter (1 8) of from 5 cm to 50 cm, such as from 15 cm to 25 cm.

[0081] In some embodiments, the subsurface gas sampler further comprises a mesh or screen (134) operatively coupled to the one or more inlets to prevent soil intrusion into inlets.

[0082] In some embodiments, the subsurface gas sampler further comprises a drain (136) to remove accumulating water from sampling chamber. In some embodiments, the control unit is operatively connected to the drain to allow for opening and closing of the drain.

[0083] In some embodiments, the subsurface gas sampler terminates at a distal end (140), and wherein the distal end is tapered, hardened, or a combination thereof to facilitate placement in the soil.

[0084] The control unit can function to operate the gas sensor unit, operate other elements of the system modulating gas flow through the system, and receive and store measurements from the gas sensor unit. In some embodiments, the control unit can communicate with an external computing system (e.g., wirelessly, for example, via Bluetooth or cellular communication). The external computing system can direct sensor operation and received and process measurements from the gas sensor unit (e.g., along with other information such as sensor location, for example from an onboard GPS unit, time / date of measurement, weather information, etc.).

[0085] The ambient air control element (124) can comprise, for example, a valve configured to direct and control a flow of ambient air from a position external to the sensor housing to the gas sensor unit (114). In some embodiments, the system further comprises a pump (158) to direct gas from the sampling chamber through the sample inlet and to the gas sensor unit. In some embodiments, the control unit is operatively connected to the pump.

[0086] In some embodiments, the system further comprises a temperature control (150) unit configured to regulate a temperature of the gas sample. In certain embodiments, the temperature control unit is configured to regulate the temperature of the gas sample at a temperature of from 15 °C to 40°C.

[0087] In some embodiments, the sample inlet further comprises a humidity control element (152). In certain embodiments, the humidity control element comprises a length of Nafion tubing.

[0088] In some embodiments, the system further comprises a GPS unit (154). In some embodiments, the GPS unit is present in the subsurface gas sampler. In certain embodiments, the GPS reports a location of the subsurface gas sampler to the controller. In some embodiments, the GPS unit is present in the sensor assembly. In certain embodiments, the GPS reports a position to the controller.

[0089] In some embodiments, the sensor assembly is detatchably connectable to the subsurface gas sampler (e.g., between 118 and 112). In certain embodiments, the sampler port is detatchably connectable the sampler outlet of the subsurface gas sampler. In some embodiments, the sample inlet fluidly connects the sampling chamber to the gas sensor unit when the sensor assembly is connected to the subsurface gas sampler.

[0090] Gas Sensor Units

[0091] The gas sensor unit (114) can comprise a nitrous oxide sensor, a NOx sensor, a CO2 sensor, a water sensor, a methane sensor, an ammonia sensor, or any combination thereof. In certain embodiments, the gas sensor unit (114) comprises a nitrous oxide sensor (142) and a NOx sensor (144).

[0092] Figure 16 illustrates gas flow through the example systems described herein, including through the gas sensor unit. In some embodiments, the nitrous oxide sensor and the NOx sensor are fluidly connected in parallel, as schematically illustrated in Figure 16.

[0093] The rationale for measuring certain gases in the soil as well as example sensors that can be incorporated within the gas sensor units are described in more detail below. The concentration of gases, including nitric oxides (NOX), nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) can be measured using a variety of sensors. In some embodiments, one or more sensors can be positioned within a probe that can be used to measure subsurface gas concentrations. Use of sensors provide a major advantage over use of instruments (such as FTIR, gas chromatography, laser spectroscopy) in that sensors require minimal human intervention and can provide real time data over extended periods of time.

[0094] Target Gases

[0095] The motivation for measuring NOx and N2O, as well as suitable sensor designs for measuring NOx and N2O, are described below. Sensors for other gases (e.g., methane, carbon dioxide, ammonia, water vapor, etc.) can also be incorporated into the gas sensor unit, if desired for particular applications. Measurement of these gases can provide a fingerprint of metabolic activity ongoing within the soil that can be used to determine one or more characteristics of soil microbial health within a soil sample. Measurement of these gases can be used by farmers, agronomists, and others to monitor soil health and make informed soil management and / or crop management decisions.

[0096] Nitrification and denitrification determine the evolution of the nitrogen oxides within the soil. Nitrification reactions occur when there is source of nitrogen (such as fertilizer N) resulting in the formation of nitrates. Under conditions where the level of oxygen is deficient, the denitrification process will begin, resulting in conversion of nitrates to nitrogen oxides, and eventually to nitrogen. If the soil is wet, then diffusion of oxygen will be impeded resulting in situation more favorable for denitrification.

[0097] Methane and CO2 can be considered as the most reduced and most oxidized species of carbon present in soils, all other organic molecules are intermediates in this redox reaction. Methane producing bacteria known as methanogens in soils only become active in anaerobic, highly reducing conditions, this being the reason why in anaerobic soils such as rice paddies are a source of methane. Methane oxidizing bacteria, known as methanothrops function in an aerobic environment. Nitrogenous fertilizers will inhibit methane oxidation.

[0098] Production of ammonia from fertilizers such as urea is mediated by the urease enzyme. Ammonium salts as fertilizers usually do not lead to NH3 production. Applying urea fertilizers to subsurface soils will lead to NH3 production in the subsurface. Ammonia volatilization and thereby loss is a significant economic loss and well as cause of air pollution.

[0099] As described herein, the gaseous end products of soil biological cycles, including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), nitric oxides (NO and NO2), and combinations thereof, can serve as measurable analytes that can be quantified to assess the microbial health of soil samples. The levels of other relevant gaseous analytes (e.g., ammonia, water, etc.) can also be measured. For example, the levels of one or more of these gases present within a soil surface (e.g., measured by a probe placed within the soil, such as at a depth of from 1 inch to 24 inches) can be correlated to the concentration of microbes in the soil (e.g., by comparison to, for example, a standard curve), allowing the measurement of the levels of one or more of these gases to readily provide information regarding the presence of microbes within a soil sample (e.g., the concentration of microbes, the species of microbes present, or a combination thereof). This information can be used to assess the microbial health of soil, which can then be used, for example, to inform soil microbial management and / or crop management decisions. In some embodiments, the concentration of multiple gases in the soil can be measured (e.g., by a probe placed within the soil, such as at a depth of from 1 inch to 24 inches) simultaneously and then correlated to provide information regarding the presence of microbes within a soil sample (e.g., the concentration of microbes, the species of microbes present, or a combination thereof). In certain examples, the concentration of two, three, four, five, or six of CO2, CH4, N2O, NO, NO2, or ammonia gas can be measured within the soil sample, and fed into a model that provides information regarding the presence of microbes within a soil sample (e.g., the concentration of microbes, the species of microbes present, or a combination thereof).

[0100] Besides the microbes, gas emissions can be dependent on other factors, including pH, soil texture, soil mineralogy, temperature, and soil water content, which combined together gives the status of soil health. The gases above are products of metabolism of carbon and nitrogen containing species is the soil. The concentrations of the microbe-initiated gases can be input to model(s) that integrate the data to provide information about the soil microbial health, which in a global sense involves microbial biomass, microbe community composition and group abundance. The model(s) outputs can provide information regarding nutrient cycling and soil fertility. Along with other physical and chemical information, agriculturalists can use the microbe-initiated gas emissions to make informed decisions regarding soil management (e.g., the addition of soil amendments), crop selection, etc.

[0101] In some embodiments, methods can involve real time and continuous measurement of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and nitric oxide (NO and NO2) gases present in the subsoil and real-time modeling of this data to generate a comprehensive picture of the soil microbial health. Highly selective and sensitive small-footprint sensors provide information on the gas concentrations. For a certain area under consideration, multiple measurements spread across the land can be used to provide statistically sound data for reliable predictions and / or to assess variations in soil quality, for example, in different regions of a field. In order to make the predictions robust, surface measurements of these gases, along with temperature, soil moisture and soil pH are also relevant. Because of the complexity of the soil microbiome, the models can employ pattern recognition techniques and inform about the global nature of the microbial health. Model prediction examples include extent of microbial diversity and microbial mass. Based on the model output, active intervention can include microbial addition, suppression or need for soil management practices.

[0102] Soil microbes, biological communities and the functions they perform are very complex and dynamic and not easily interpreted for field practices. These methods can provide an opportunity for agriculturalists to obtain information about the microbial community of their fields, and will inform their crop management strategies, including tillage, crop rotation cover cropping, and adding compost, manure, and adding and suppressing microbes.

[0103] N2O Emissions

[0104] N2O is 298 times more potent as a greenhouse gas (GHG) as compared to CO2, persists in the atmosphere for about 116 years, and N2O emissions are increasing at a faster rate than other GHGs, with a 30% increase observed just over the last forty years. N2O also contributes to stratospheric ozone depletion. Its concentration is increasing with industrial and agricultural development, from 270 parts per billion (ppb) in 1750 to 331 in 2018.

[0105] NOx Emission

[0106] Reaction of nitrogen oxides NOX(= NO+NO2) with hydroxyl radicals (OH) is responsible for the formation of O3 and aerosols, which impact human health. NOx also decreases crop production. Globally, fossil fuel, biomass, and biofuel burning and wildfires account for 76% of total NOx emissions. Natural soils account for 12%, agricultural soils 8%, and aviation and lightning around 4% of NOx. EPA estimates that in the US for 2005-2018, there was a 54% decrease in NOx from anthropogenic sources due to regulations, but, possibly due to soil emissions, tropospheric NOx did not decrease post 2009, and O3 concentration actually saw a rise.

[0107] Agricultural practices lead to NOx and N2O

[0108] As illustrated in Figure 1, N-based synthetic fertilizers include ammonia-based compounds: urea-ammonium-nitrate, calcium- ammonia-nitrate, anhydrous ammonia, ammonium sulfate, and urea. Soil microorganisms convert N in the fertilizer to NOx and N2O via enzymatic reactions. This chemistry is complex and dependent on the fertilizers, soil texture, bulk density, precipitation and microbial activity in soils, temperature, and soil pH. Simplified, nitrification involves the oxidation of NH3 into nitrates: NH3 — NO2 — NO3-(dependent on alkalinity, aerobic conditions), whereas denitrification produces NO and N2O: NO2— NO— N2O— N2 (dependent on acidity, anaerobic conditions). N losses arising from excess fertilizer use impacts the environment via leaching, run-off, and eutrophication of vulnerable ecosystems. One study which measured both NO and N2O after fertilization of maize fields with NH3 fertilizer (280 kg(N) ha-1) found that the total N loss to the atmosphere is between 30-110 kg(N) ha1(average is 28% of fertilizer(N) used) and appear as 1% NH3, 40% and NO, 14% as N2O and 46% as N2. In California, fertilized croplands account for 20 to 32% of total NOXemissions, whereas natural soils account for 5 to 9%.

[0109] Climate change also exacerbates global NOXand N2O, manifested by alteration in rain patterns. Reduction in rainfall and drought, dry and well-aerated soils favor NOXover N2O, whereas lower O2 promotes N2O. Soil nitrification and denitrification increases with ambient temperature, with subsequent growth in NOx and N2O emissions. Climate change induced arid soils enhance NOx production relative to N2O, and nitrate formation via nitrification.

[0110] N2O sensors

[0111] In some embodiments, the nitrous oxide sensor comprises a non-dispersive infrared sensor (NDIR) sensor.

[0112] In some embodiments, the nitrous oxide sensor has a limit of detection of 500 ppb or less. In certain embodiments, the nitrous oxide sensor has a limit of detection of from 100-500 ppb. In some embodiments, the nitrous oxide sensor has an upper limit of detection of greater than 1 ppm, such as an upper limit of detection of about 5 ppm or 10 ppm.

[0113] An example N2O sensor is shown in Figure 18. This sensor is capable of N2O measurements in the 300 ppb to 10 ppm range suitable for agricultural applications.

[0114] The principal components of an NDIR sensor are an infrared source, a sample chamber, a light filter, and an infrared detector. IR light is emitted from the infrared source and directed to the sample chamber as shown in Figure 18. The gas in the sample chamber absorbs the IR light at wavelengths specific to the gas species. The absorption of IR light by the gas depends on the species concentration according to the Beer-Lambert Law. After passing through the sample chamber, the attenuated IR light passes through a filter at the end of the optical path. Light filters are selected to allow through only the specific wavelengths of light that are absorbed by the gas species of interest. The filtered light is then detected by the infrared detector. Quantitative gas species measurement is achieved by back calculating from the IR attenuation the concentration through the Beer-Lambert Law. The IR absorption spectrum and light filter wavelengths are shown in Figure 19. In some embodiments, the system further comprises a soda lime filter (148) for removing CO2 from a gas sample prior to a gas sample entering the nitrous oxide sensor.

[0115] NOx sensor

[0116] In some embodiments, the NOx sensor can comprise a potentiometric NOx sensor. In some embodiments, the NOx sensor comprises a base substrate; and a plurality of potentiometric sensor units connected in series and coupled to the base substrate. Each potentiometric sensor unit can comprise an electrolyte layer disposed on the base substrate; a two-part sensing electrode comprising a layer of tungsten oxide (WO3) disposed on a platinum (Pt) contact; and a reference electrode comprising platinum (Pt). In some embodiments, the reference electrode comprises Pt- loaded zeolite Y (Pt-Y).

[0117] In some embodiments, the NOx sensor has a limit of detection of from 5ppb to 5 ppm (e.g., from 5-500 ppb, or from 5-100 ppb). In certain embodiments, the NOx sensor has a limit of detection of 50 ppb or less. In some embodiments, the NOx sensor has an upper limit of detection of greater than 1 ppm, such as an upper limit of detection of about 5 ppm or 10 ppm.

[0118] An example electrochemical NOx solid state sensor that has been demonstrated to measure NOx in the ppb-to-ppm range is shown in Figure 20. Figure 20 (panel a) is a schematic of the total NOx sensor design. The sensor works on the well-studied principle of mixed- potential potentiometric sensing. The sensor uses WO3 sensing electrode and Pt-loaded zeolite Y (PtY) acting as the reference electrode in a planar geometry. WO3 has a very poor catalytic reactivity for NOx equilibration, therefore the gas will pass through the WO3 layer without light filter being modified and then take part in the NOXelectrochemistry at the triple-point boundary (TPB: WOVYSZ / gas). On the other hand, Pt-loaded zeolite Y (Pt-Y) has a very high catalytic reactivity with NOx. The NOx gas passes through the PtY is equilibrated, prior to reaching the TPB, and acts as a suitable reference. The measured signal is due to the electrochemical reaction happening at the sensing electrode. The second innovation was to use a Pt- zeolite Y filter separate and ahead of the potentiometric YSZ based sensor. The NOx passing through the zeolite gets equilibrated to a particular NO + NO2 composition depending on the temperature of the zeolite layer and gives the same response to NO and NO2 or mixtures, thereof (Figure 21). By maintaining a temperature differential between the filter and the sensor, the sensitivity of the sensor can be increased. A zeolite catalytic layer can be included to eliminate interference to other oxidizable gases, such as carbon monoxide, ammonia and hydrocarbons which can all be found in soil. The sensors can be packed in series in series as shown in Figure 20 (dimensions of 4 mm), which allows for measurement of ppb range total NOX. The NOx sensor can be manufactured by ceramic screen-printing methods with a dynamic range of 10ppb-300ppb NOx with + / - 10% accuracy. An example NOx sensor package is shown in Figure 22.

[0119] In some embodiments, the system further comprises a heater operatively coupled to the NOx sensor. In some embodiments, the heater is configured to heat the NOx sensor to a temperature of from 250°C to 500°C.

[0120] In some embodiments, the system further comprises a NOx scrubber (146) for removing NO from a gas sample prior to a gas sample entering the NOx sensor. In certain embodiments, the NOx scrubber comprises KMnO4.

[0121] Such sensors are described, for example, in WO 2008 / 103311, WO 2014 / 143782, U.S. Patent No. 8,012,323, and U.S. Patent No. 6,764,591, each of which is hereby incorporated by reference in its entirety.

[0122] Carbon Dioxide

[0123] If desired, the gas sensor unit can comprise a carbon dioxide sensor.

[0124] In some embodiments, CO2 concentrations can be measured using a potentiometric sensor with a L13PO4 electrolyte and a BaCOrcoated LECO3 sensing electrode. Such sensors can be used to measure CO2 over a wide range of concentrations (100 ppm to 20%) at 500°C with minimal interference to humidity. The active element in the sensing electrode for CO2 detection is Li2CO3. However, sensors with just Li2CO3 electrodes showed interference from humidity, which was eliminated by use of the BaCCh layer. Infrared spectroscopy as well as electrode preparations involving heating above the eutectic temperature of BaCO3-Li2CO3 suggests that the BaCO i layer wets the Li2CO3 electrode surface, making it more hydrophobic and thereby reducing the interference from humidity. Humidity interference in agricultural applications would be a major impediment. These CO2 sensors can be readily miniaturized with footprints of the order of millimeters.

[0125] Examples of carbon dioxide sensors include those described in U.S. Patent No. 8,057,653, which is incorporated herein by reference in its entirety.

[0126] Methane

[0127] If desired, the gas sensor unit can comprise a methane sensor. Example methane sensors can employ non-dispersive infrared (NDIR) technology using a compact pentahedron gas-cell. A paraboloid concentrator, two biconvex lenses and five planar mirrors were used to set up the pentahedron structure. The gas cell is endowed with a 170 mm optical path length with a volume of 19.8 mL. The gas-cell was integrated with a mid-infrared light source and a detector as the optical part of the sensor. Concerning the electrical part, a microcontroller was used to generate the driving signal for the IR source, and the signal from the detector was sampled by an analog- to-digital converter. A static volumetric method was employed for the experimental setup, and 20 different concentration CH4 samples were prepared to study the sensor’s evaluation, which revealed a lo detection limit of 2.96 parts-per-million (ppm) with a 43 s averaging time.

[0128] Ammonia

[0129] If desired, the gas sensor unit can comprise a ammonia sensor. Examples of ammonia sensors include resistance-based sensors, such as those described in WO 2017 / 095475, which is incorporated herein by reference in its entirety.

[0130] Methods of Use

[0131] Currently, farmers follow fertilizer recommendations for the respective crop and soil type and try not to overapply fertilizers. However, it has been pointed out that the NO and N2O production from fertilized lands varies widely with the soil chemistry, climate, and cultivation practices and coupled with the spatial and temporal heterogeneity of the emissions requires field measurements for the emission gases to accurately track the emissions. If inexpensive and highly selective NOXand N2O sensors that provide real-time soil subsurface data over annual cultivation cycles are available, then field measurements become possible on a large scale.

[0132] Using the devices and systems described herein (e.g., equipped to quantify subsurface NOXand N2O gas concentrations), NOXand N2O can measured over the entire growing season to account for seasonal changes, the influence of crops can be evaluated, and tillage, irrigation, and manure practices can be optimized. Optimization of N-species would also lead to a decrease in NO3" leaching in water. The result will be to increase N use efficiency of fertilizers. Currently, N2O emissions from all fertilizers is typically estimated at 1% of applied N (IPCC, 2006). Success of more precise nitrogen management will also help farmers with obtaining carbon credit. Soil subsurface creates NOXand N2O and when this NOXand N2O moves beyond the surface, they become a significant source of surface-emitted NOXand N2O. The devices and systems presented here can measure concentrations subsurface as well as above ground (e.g., ambient gas concentrations), and can be readily installed at different locations without disturbing normal field operations.

[0133] Sampler locations can measured and / or tracked using GPS, and placed at intervals within a field to provide information about gas concentrations across and / or at particular locations within a field. In some cases, the subsurface gas sampler can be detachable from the sensor assembly. In these embodiments, multiple subsurface gas samplers can be positioned within the soil, and the sensor assembly can be periodically attached to subsurface gas samplers to collect gas readings. These systems and devices make it practical for farmers to have detailed knowledge of the state of their agricultural field.

[0134] An economical and practical approach to measuring nitrogen oxide emissions will enable better measurements and data collection regarding greenhouse gas emissions in agricultural management systems. Based on the ground-truth data, better decisions can be made and fertilizer can be used more efficiently. Farmers will be able to decrease the contribution of greenhouse gas N2O and air-polluting NOx without influencing crop yields and can realize carbon credits in a meaningful fashion. This product will help bridge the data gap critical to catalyzing new market incentives for innovative practices that reduce agricultural production-related emissions. The systems and methods described herein can be used to improve fertilizer-use management, soil health, and greenhouse gas emissions reduction.

[0135] To minimize the impact of climate change on agriculture, several strategies including sequestering carbon in the soil, reducing soil erosion, conserving soil moisture and temperature, enhancing soil fertility, and reducing NOXand N2O gas emissions are necessary. In particular, for minimizing NOXand N2O emissions, agricultural management practices focused on fertilization, irrigation, and tillage and cover crops are necessary. This will require appropriate use of fertilizers, conservation tillage, use of biochar and balancing soil nutrients and acidification, avoiding eutrophication and nutrient run-off, and promoting biological diversity. Fertilizer inputs that exceed crop N requirements need to be monitored. It has been pointed out that NOXand N2O emissions can be reduced by 1) making changes in the rates, timing and type of nitrogen fertilizer applications; 2) using slow-release fertilizers that control the formation of nitrates; 3) using fertilizers with nitrification agents (prevent NH4+to NO3 ) and urease inhibitors (control NH? formation); 4) using organic fertilizers (manure, compost and plant residues) with appropriate timing relative to N fertilizers; 5) influencing the biological processes that cause nitrate leaching and produce GHG; 6) use cover crops that consume residual N; and 7) minimizing soil disturbance using conservation tillage practices But how can farmers make these decisions? If farmers have easy-to-use tools to measure N2O and NOX(such as the devices and systems described herein), then decisions about fertilizer management can be made based on sound data.

[0136] Example instructions for measuring the soil gas emissions can include the following: • Insert the subsurface gas sampler (probe) into the soil

[0137] • Warm up the sensors

[0138] • Rotate the bottom core of the probe to make sure that gases from the soil can enter the bottom chamber for a defined period of time extending from minutes to hours

[0139] • Block the pore system

[0140] • Sweep the collected gases into the sensing chamber and make measurements with the sensors

[0141] • Close the valve between the probe extending into the soil and the top chamber

[0142] • Make sensing measurements for estimating ambient gases

[0143] Some example implications of the devices and systems described herein include the following (e.g., as the devices and systems described herein relate to modern agriculture).

[0144] • By 2050 we will need 50% more food, this necessitates the increase of N input via fertilizers.

[0145] • N input into soils helps with plant yield.

[0146] • N input into soils not taken up by plants leads to production of environmentally adverse nitrates and polluting NOx and greenhouse N2O gas.

[0147] • It is necessary to figure out how to accomplish the increased N input yet minimizing nitrate run off and minimizing NOx and N2O emissions.

[0148] • Another option is to increase agricultural land, which is not good for the environment

[0149] • Need to match N input via fertilizers to crop need for the N.

[0150] • 4R related to optimum fertilizer use for increased nitrogen use efficiency (NUE): Right time, Right place, Right nutrient, Right Rate.

[0151] • By measuring nitrogen oxide emissions from within the soil, the devices and systems described herein can promote optimum fertilizer use by promoting the 4Rs.

[0152] • the devices and systems described herein can also help in lowering NOx and N2O emissions, and nitrate production.

[0153] • the devices and systems described herein can also assist in enforcing regulations related to polluting and greenhouse gas emissions.

[0154] While the methods and systems have been described in connection with preferred embodiments and specific examples, it is not intended that the scope be limited to the particular embodiments set forth, as the embodiments herein are intended in all respects to be illustrative rather than restrictive. Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; the number or type of embodiments described in the specification.

[0155] Throughout this application, various publications may be referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the methods and systems pertain.

[0156] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope or spirit. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit being indicated by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A gas measurement system for measuring gas emissions from soil, the device comprising:(a) a subsurface gas sampler positionable within the soil, the subsurface gas sampler comprising:(i) a sampler housing at least partially defining a sampling chamber;(ii) one or more inlets for receiving gas emissions from soil into the sampling chamber; and(iii) a sampler outlet; and(b) a sensor assembly interfacing with the subsurface gas sampler; the sensor assembly comprising:(i) a gas sensor unit for measuring a concentration of one or more gases within a gas sample;(ii) a sensor housing enclosing the gas sensor and comprising a sampler port coupled to the sampler outlet of the subsurface gas sampler;(iii) a sample inlet fluidly connecting the sampling chamber to the gas sensor unit;(iv) an ambient air inlet fluidly connected to the gas sensor unit via an ambient air control element, wherein the ambient air control element is configured to direct and control a flow of ambient air from a position external to the sensor housing to the gas sensor unit; and(v) a control unit operatively connected to the gas sensor unit and adapted to receive and store measurements from the gas sensor unit.

2. The system of claim 1 , wherein the subsurface gas sampler further comprises a sample release valve controlling flow of gas emissions from the sampling chamber to the sample inlet when the sensor assembly is connected to the subsurface gas sampler.

3. The system of claim 2, wherein the sample release valve is actuatable between a first position where gas emissions present in the sampling chamber cannot flow from the sampling chamber to a second position wherein gas emissions present in the sampling chamber can flow from the sampling chamber.

4. The system of claim 3, wherein the control unit is operatively connected to the sample release valve such that the control unit directs actuation of the sample release valve between the first position and the second position.

5. The system of claim 4, wherein the control unit is wirelessly connected to the sample release valve.

6. The system of any of claims 1-5, wherein the subsurface gas sampler further comprises one or more inlet controls configured to control flow of gas emissions from the soil through the one or more inlets and into the sampling chamber.

7. The system of claim 6, wherein the one or more inlet controls are actuatable between a first position where the one or more inlets are sealed and a second position wherein the one or more inlets are open and gas emissions can pass from soil into sampling chamber.

8. The system of any of claims 6-7, wherein the one or more inlet controls comprise a rotatable member that rotatably actuates between the first position and the second position.

9. The system of any of claims 7-8, wherein the control unit is operatively connected to the one or more inlet controls such that the control unit directs actuation of the one or more inlet controls between the first position and the second position.

10. The system of claim 9, wherein the control unit is wirelessly connected to the one or more inlet controls.

11. The system of any of claims 1-10, wherein the one or more inlets selectively permit passage of gas emissions from soil while excluding water and soil from entering the sampling chamber12. The system of claim 11 , wherein the one or more inlets comprise a membrane that permits transmembrane permeation of gas emissions from soil while excluding water and soil.

13. The system of claim 12, wherein the membrane comprises a selectively permeable membrane.

14. The system of any of claims 1-13, wherein the one or more inlets are circumferentially disposed about the sampler housing.

15. The system of any of claims 1-11, wherein the sampler housing has a length, and wherein the one or more inlets comprise a plurality of inlets disposed at varying points along the length of the sampler housing.

16. The system of claim 15, wherein the one or more inlets comprise a plurality of inlets disposed at regular intervals along the length of the sampler housing.

17. The system of claim 16, wherein the regular intervals correspond to defined depths beneath the soil when the subsurface gas sampler is positioned within the soil.

18. The system of claim 17, wherein the defined depths range from 2 cm to 60 cm beneath the soil when the subsurface gas sampler is positioned within the soil.

19. The system of any of claims 1-18, wherein the subsurface gas sampler further comprises one or more inlet controls configured to control flow of gas emissions from the soil through the one or more inlets and into the sampling chamber; wherein the one or more inlet controls are configured to allow a user to selectively control flow of gas emissions from the soil through selected inlets disposed at varying points along the length of the sampler housing.

20. The system of claim 19, wherein the one or more inlets comprise a plurality of inlets disposed at regular intervals along the length of the sampler housing.

21. The system of claim 20, wherein the regular intervals comprise every centimeter, every 2 cm, every 3 cm, every 4 cm, every 5 cm, every 6 cm, every 7 cm, every 8 cm, every 9 cm, or every 10 cm along the length of the sampler housing.

22. The system of any of claims 1-21 , wherein the sampler housing has a length of from 5 cm to 75 cm.

23. The system of any of claims 1-22, wherein the subsurface gas sampler further comprises a mesh or screen operatively coupled to the one or more inlets to prevent soil intrusion into inlets.

24. The system of any of claims 1-23, wherein the subsurface gas sampler further comprises a drain to remove accumulating water from sampling chamber.

25. The system of claim 24, wherein the control unit is operatively connected to the drain to allow for opening and closing of the drain.

26. The system of any of claims 1-25, wherein the sampler housing has a diameter of from 5 cm to 50 cm, such as from 15 cm to 25 cm.

27. The system of any of claims 1-26, further comprising a pump to direct gas from the sampling chamber through the sample inlet and to the gas sensor unit.

28. The system of claim 27, wherein the control unit is operatively connected to the pump.

29. The system of any of claims 1-28, wherein the subsurface gas sampler terminates at a distal end, and wherein the distal end is tapered, hardened, or a combination thereof to facilitate placement in the soil.

30. The system of any of claims 1-29, wherein the gas sensor unit comprises a nitrous oxide sensor, a NOx sensor, a CO2 sensor, a water sensor, a methane sensor, an ammonia sensor, or any combination thereof.

31. The system of any of claims 1-30, wherein the gas sensor unit comprises a nitrous oxide sensor and a NOx sensor.

32. The system of any of claims 30-31, wherein the NOx sensor comprisesa base substrate; and a plurality of potentiometric sensor units connected in series and coupled to the base substrate, each potentiometric sensor unit comprising: an electrolyte layer disposed on the base substrate; a two-part sensing electrode comprising a layer of tungsten oxide (WO3) disposed on a platinum (Pt) contact; and a reference electrode comprising platinum (Pt).

33. The system of claim 32, wherein the reference electrode comprises Pt-loaded zeolite Y (Pt-Y).

34. The system of any of claims 30-33, wherein the NOx sensor has a limit of detection of from 5ppb to 5 ppm.

35. The system of claim 34, wherein the NOx sensor has a limit of detection of from 5-100 ppb.

36. The system of claim 35, wherein the NOx sensor has a limit of detection of 50 ppb or less.

37. The system of any of claims 30-33, wherein the NOx sensor has an upper limit of detection of greater than 1 ppm, such as an upper limit of detection of about 5 ppm or 10 ppm.

38. The system of any of claims 1-37, wherein the system further comprises a heater operatively coupled to the NOx sensor.

39. The system of claim 38, wherein the heater is configured to heat the NOx sensor to a temperature of from 250°C to 500°C.

40. The system of any of claims 1-39, wherein the system further comprises a NOx scrubber for removing NO from a gas sample prior to a gas sample entering the NOx sensor.

41. The system of claim 40, wherein the NOx scrubber comprises KMnO4.

42. The system of any of claims 1-41, wherein the nitrous oxide sensor comprises an NDIR sensor.

43. The system of any of claims 1-42, wherein nitrous oxide sensor has a limit of detection of 500 ppb or less.

44. The system of any of claims 1-43, wherein nitrous oxide sensor has a limit of detection of from 100-500 ppb.

45. The system of any of claims 1-44, wherein nitrous oxide sensor has an upper limit of detection of greater than 1 ppm, such as an upper limit of detection of about 5 ppm or 10 ppm.

46. The system of any of claims 1-45, wherein the system further comprises a soda lime filter for removing CO2 from a gas sample prior to a gas sample entering the nitrous oxide sensor.

47. The system of any of claims 1-46, wherein the nitrous oxide sensor and the NOx sensor are fluidly connected in parallel.

48. The system of any of claims 1-47, further comprising a temperature control unit configured to regulate a temperature of the gas sample.

49. The system of claim 48, wherein the temperature control unit is configured to regulate the temperature of the gas sample at a temperature of from 15°C to 40°C.

50. The system of any of claims 1-49, wherein the sample inlet further comprises a humidity control element.

51. The system of claim 50, wherein the humidity control element comprises a length of Nafion tubing.

52. The system of any of claims 1-51, wherein the system further comprises a GPS unit.

53. The system of claim 52, wherein the GPS unit is present in the subsurface gas sampler.

54. The system of claim 53, wherein the GPS reports a location of the subsurface gas sampler to the controller.

55. The system of claim 53, wherein the GPS unit is present in the sensor assembly.

56. The system of claim 55, wherein the GPS reports a position to the controller.

57. The system of any of claims 1-56, wherein the sensor assembly is detatchably connectable to the subsurface gas sampler.

58. The system of claim 57, wherein the sampler port is detatchably connectable the sampler outlet of the subsurface gas sampler.

59. The system of any of claims 57-58, wherein the sample inlet fluidly connects the sampling chamber to the gas sensor unit when the sensor assembly is connected to the subsurface gas sampler.

60. A gas measurement system for measuring gas emissions from soil, the device comprising:(a) a subsurface gas sampler positionable within the soil, the subsurface gas sampler comprising:(i) a sampler housing at least partially defining a sampling chamber;(ii) one or more inlets for receiving gas emissions from soil into the sampling chamber; and(iii) a sampler outlet; and(b) a sensor assembly detatchably connectable to the subsurface gas sampler; the sensor assembly comprising:(i) a gas sensor unit for measuring a concentration of one or more gases within a gas sample;(ii) a sensor housing enclosing the gas sensor and comprising a sampler port detatchably connectable the sampler outlet of the subsurface gas sampler;(iii) a sample inlet fluidly connecting the sampling chamber to the gas sensor unit when the sensor assembly is connected to the subsurface gas sampler;(iv) an ambient air inlet fluidly connected to the gas sensor unit via an ambient air control element, wherein the ambient air control element is configured to direct and control a flow of ambient air from a position external to the sensor housing to the gas sensor unit; and(v) a control unit operatively connected to the gas sensor unit and adapted to receive and store measurements from the gas sensor unit.

61. A gas measurement system for measuring gas emissions from soil, the device comprising:(a) a subsurface gas sampler positionable within the soil, the subsurface gas sampler comprising:(i) a sampler housing at least partially defining a sampling chamber;(ii) one or more inlets for receiving gas emissions from soil into the sampling chamber, wherein the one or more inlets selectively permit passage of gas emissions from soil while excluding water and soil from entering the sampling chamber; and(iii) a sampler outlet; and(b) a sensor assembly interfacing with the subsurface gas sampler; the sensor assembly comprising:(i) a gas sensor unit for measuring a concentration of one or more gases within a gas sample;(ii) a sensor housing enclosing the gas sensor and comprising a sampler port coupled to the sampler outlet of the subsurface gas sampler;(iii) a sample inlet fluidly connecting the sampling chamber to the gas sensor unit;(iv) an ambient air inlet fluidly connected to the gas sensor unit via an ambient air control element, wherein the ambient air control element is configured to direct and control a flow of ambient air from a position external to the sensor housing to the gas sensor unit; and(v) a control unit operatively connected to the gas sensor unit and adapted to receive and store measurements from the gas sensor unit.

62. The use of the system of any of claims 1-61 to measure a subsurface concentration of a gas present in the soil.

63. The use of claim 62, comprising making two or more measurements within a 24-hour time period.

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