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. 2021 Mar 2;21(5):1701.
doi: 10.3390/s21051701.

Low-Cost Fluorescence Sensor for Ammonia Measurement in Livestock Houses

Jesper Nørlem Kamp  1 , Lise Lotte Sørensen  2 , Michael Jørgen Hansen  1 , Tavs Nyord  1 , Anders Feilberg  1
Affiliations

Low-Cost Fluorescence Sensor for Ammonia Measurement in Livestock Houses

Jesper Nørlem Kamp et al. Sensors (Basel). .

Abstract

Measurements of ammonia with inexpensive and reliable sensors are necessary to obtain information about e.g., ammonia emissions. The concentration information is needed for mitigation technologies and documentation of existing technologies in agriculture. A flow-based fluorescence sensor to measure ammonia gas was developed. The automated sensor is robust, flexible and made from inexpensive components. Ammonia is transferred to water in a miniaturized scrubber with high transfer efficiency (>99%) and reacts with o-phthalaldehyde and sulfite (pH 11) to form a fluorescent adduct, which is detected with a photodiode. Laboratory calibrations with standard gas show good linearity over a dynamic range from 0.03 to 14 ppm, and the detection limit of the analyzer based on three-times the standard deviation of blank noise was approximately 10 ppb. The sampling frequency is 0.1 to 10 s, which can easily be changed through serial commands along with UV LED current and filter length. Parallel measurements with a cavity ring-down spectroscopy analyzer in a pig house show good agreement (R2 = 0.99). The fluorescence sensor has the potential to provide ammonia gas measurements in an agricultural environment with high time resolution and linearity over a broad range of concentrations.

Keywords: NH3; ammonia; fluorescence sensor; pigs.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure A1
Figure A1
Picture of the scrubber with water inflow at the top (1) and water outflow at the bottom (4). Air inlet is at the bottom (3) and air outlet is at the top (2).
Figure A2
Figure A2
Picture of the fluorescence detector unit with the detector on the left and UV LED on the front.
Figure 1
Figure 1
Schematics of the fluorescence sensor system with scrubber on the right and detector on the left. Six pumps handle the liquid and gas flow.
Figure 2
Figure 2
Polyether ether ketone (PEEK) flow cell with photo diode and LED installed in mounts. (a) shows an end view of a computer aided design (CAD) drawing of the flow cell. The two circles indicate the two ball lenses. (b) shows a side view of a CAD drawing of the flow cell. The two circles indicate the two ball lenses and water flow is from left to right.
Figure 3
Figure 3
Laboratory calibration of the NH3 sensor with a dynamic dilution system of NH3 and N2 standard gasses. The blue line shows the linear regression line, y = 5.84x + 12121, R2 = 0.9990.
Figure 4
Figure 4
Fluorescence sensor output response to changes in UV LED current with a fixed NH3 gas concentration of 13.958 ppm. The blue line shows the linear regression line, y = 82.14x − 5591.1, R2 = 0.9965. The two red point show the saturated points, which are not included in the linear regression.
Figure 5
Figure 5
Linear regression between NH3 concentrations measured with a cavity ring-down spectroscopy (CRDS) analyzer and fluorescence detector in pig houses. The blue line shows the linear regression line, y = 0.97x + 45, R2 = 0.9903.
Figure 6
Figure 6
Minutely mean concentration for all fluorescence sensor data and only CRDS from the same position, i.e., two measurement cycles per hour for the CRDS.
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