HT8700E Open-path NH3 Analyzer

HT8700E Open-path NH₃ Analyzer
 
Fast Atmospheric Ammonia Measurements
High Sensitivity & Resolution
Portable Design & Low Power Consumption



Introduction
Atmospheric ammonia (NH₃) is a precursor to fine particulate matter, with implications for air quality and climate change. In the past, measurements of ammonia flux were limited by detection challenges, resulting in large errors in the estimation of NH₃ emissions around the world.
Our HT8700E is an open-path atmospheric NH₃ analyzer based on the next-generation mid-infrared laser spectroscopy, which ensures high precision and high sensitivity of the analyzer. Compared to the traditional closed-path analyzers, the open-path configuration minimizes sampling artifacts associated with NH₃ surface adsorption onto tubing, ensuring the high-speed NH₃ measurements.
HT8700E overcomes the limitations of traditional instruments and fully satisfies the requirements of Eddy Covariance technique. The analyzer is low power, lightweight, and easy to maintain. It can adapt to a variety of remote ecological environments or be installed on a moving vehicle.
 
Features
Open Path, High Sensitivity, and Fast Response

• Ultra-sensitive NH₃ density measurement using laser spectroscopy
• No pump required
• No time delays or attenuation from adsorption on the tubing
• Fast response to large NH₃ concentration changes

Portable Design for Versatile Field Deployment

• Strong environmental adaptability and vibration resistance
• Enhanced carbon fiber opto-mechanics that minimize system drift and weight
• Heated mirrors that avoid signal loss due to condensation

Remote Field and Mobile Measurement

• Low power that can be supplied by a solar panel or battery
• Lightweight (<10kg)
• Easy installation and maintenance in a remote field or on a vehicle

Our Technology
HT8700E is based on the state-of-the-art Wavelength-Modulated Quantum Cascade Laser Absorption Spectroscopy (WM-QCLAS) technology. Recently, the advancement of QCL technology has enabled HealthyPhoton to introduce this QCL-based analyzer, which utilizes the strong absorption line of NH₃ in the mid-infrared spectral band to achieve unprecedented high-precision and high-selectivity analysis.
The basic method is to calibrate the QCL wavelength that sweeps a specific absorption spectrum line of the NH₃ molecule. The transmitted light is received by the photodetector, and the harmonic component of the transmission spectrum is extracted and analyzed.

Mid-infrared Laser Spectroscopy
Near-infrared diode lasers have been used for NH₃ detection. However, the absorption peak intensity of NH₃ molecules in the near-infrared region (~1.5um) is very low, which limits the detection accuracy. Compared to the near-infrared region, Fig. 1 shows that NH₃ has 100x stronger absorption peaks in the mid-infrared band (8-10um). We use the world's leading semiconductor QCL as an infrared laser source. Multiple reflections of the laser beam between two high-reflection mirrors exposing to the atmosphere create an effective optical path-length of several tens of meters. The absorption of the laser energy at the spectral peak is extracted using lock-in amplification of the modulated laser signal (shown in Fig. 2). There is no overlap of absorption peaks with H₂O, CO, and other atmospheric trace gases in the band we use, which ensures the anti-interference NH₃ measurement. Combined with a proprietary signal processing technology, the NH₃ fundamental transitions are efficiently detected and gas concentration is retrieved with sub-ppb sensitivity.


Fig. 1 Absorption peaks of NH₃ in the near-infrared (blue block) and mid-infrared (red block) bands

Fig. 2 Schematic diagram of the system. P&T is the environmental pressure and temperature sensor. LD&TC is the laser current drive and temperature controller. L is a QC laser source. BS is a beam splitter. M1 and M2 are two high-reflectivity mirrors in an open-path Herriott cell configuration. M3 is a mirror and R is the reference gas cell. D1/Pre-amp1 and D2/Pre-amp2 are infrared photodetectors with low noise preamplifiers for the signal and reference path, respectively. FPGA+MCU are responsible for data acquisition, processing, spectrum retrieval, and system control/communication.

The Open-path Configuration
Previously, NH₃ surface adsorption and desorption effects in closed-path analyzers limit the response time to a few seconds or longer. Our open-path configuration minimizes sampling artifacts associated with NH₃ surface adsorption onto inlet tubing. The HT8700E ensures short response time and data output at 10Hz, which meet the requirements for transient NH₃ emission measurements on a mobile platform and eddy covariance flux measurements.
 
Specifications

Items	Specifications
Resolution (1s; 0.1s/1s/10s)	0.5 ppb/ 0.15 ppb/ 0.05 ppb
Measurement Range	Typ. 0 - 10 ppm (optional 0 - 20 ppm)
Output Bandwidth	10 Hz (optional 20 Hz)
Operating Pressure Range	70 - 110 kPa
Operating Relative Humidity Range	0 - non-condensing
Operating Temperature Range	-20 ~ 45 ℃
Data Communication	RS-232
Detection Method	Wavelength Modulating Quantum Cascade Laser Absorption Spectroscopy
Power Requirements	18 to 29 VDC
Power Consumption	Nominal 50 W
Dimensions	20 cm dia, 83.4 cm height
Optical Path	0.5 m physical path; 49 m measurement path
Weight	5 kg
Environmental Adaptability	IP67

 

Items	Description
HT8700E	QCL based open-path NH3 analyzer Includes: 24VDC power adapter×1, mirror cleaning kit×1, circulating water cooling system×1, transportable instrument case×1
HT8700E-GPSv (optional)	GPS module with RS-232 output

Application Notes
On-Site Measurements at Livestock Farm
Fig. 3 shows a typical ammonia mobile analyzing system. It contains HealthPhoton HT8700E ammonia analyzer, Campbell’s CR3000 data acquisition module, GPS module, anemometer module, and real-time data processing module. The whole system can be installed on the automobile roof rack and collect 10Hz high-speed ammonia concentration data in real-time. The latitude, longitude location data, wind direction, and wind speed data are collected simultaneously by the GPS module and anemometer module. Data is synchronized and transmitted to cloud for remote data processing. The real-time concentration analysis provides a complete solution for high-speed and accurate ammonia emission monitoring and tracing.
Fig. 4 shows the tested atmospheric ammonia concentration surrounding a livestock farm. The red pin indicates the location of the farm, and the color trace is the testing route. Blue means low concentration while red means high. We found two peaks of concentration (>250 ppb) in the experiment, which are at the main entrance of the farm (349.3 ppb) and the manure dumping area, respectively. They are both ammonia emission sources, and the concentration decreases gradually as the distance increases. Fig. 5 is a sample of transient ammonia concentration data showing a short response time (< 1 second) to concentration changes. The experiment proves the system stability and reliability on a vehicle traveling for hundreds of kilometers while achieving high-speed and high-accuracy measurements of sub-ppb level ammonia.
 

Fig. 3 An ammonia mobile analyzing system based on HT8700E

Fig. 4 Map of atmospheric ammonia concentration around a livestock farm

Fig. 5 Data showing the concentration change response time less than 1 second