Natural ammonia levels in the atmosphere are in the low ppb range. Ammonia is a toxic gas and a severe irritant to the respiratory tract. Several international standards exist that define the level of toxicity for humans. Generally, short-term exposure over 15 minutes needs to be limited to 25-35 ppm and the Time-Weighed-Average (TWA) over a 8-hour period should not exceed 25 ppm. Values for Immediate Danger to Life & Health (IDLH) are at 300 ppm. Concentrations of 1’500 ppm and more can cause fatal pulmonary oedema and ammonia becomes irritating to moist skin at about 10’000 ppm. The Lower Explosive Limit (LEL) for ammonia is 15 %. Depending on conditions and sensibility, humans can first notice the smell of ammonia anywhere between a few and 50 ppm. Accidental ammonia releases are far from being rare. A survey has shown that over a 5-year period in the 90ies a total of 40’000 people were evacuated as a result of roughly 600 incidents, whereas 250 led to a total of 1’400 injuries. This shows the critical need of reliable and effective ammonia monitoring in the industry sectors mentioned below. Ammonia also contributes to poor air quality by fostering the formation of noxious dust-size airborne particles and by serving as a precursor for gound-level ozon generation.

The trend for monitoring, control and reduction of ammonia emissions has significantly increased over the past few years - mostly driven by increasingly strict environmental standards and regulations.

Emission control
While NOx reduction by 3-way catalysts has found a lot of attention in environmental protection in the past, there is a growing awareness to reduce significant NH3 emission from fuel-rich operated thermal engines or in power generation.

Heat & Power Generation: Gas and oil power & heat plants, as well as stationary diesel engines for power generation use selective catalytic reduction (SCR) to reduce NOx emissions. In this process an aqueous urea solution is injected to react with the exhaust gas. Ammonia slip occurs when over-stoichiometric amounts of urea are present. NH3 detection in mobile diagnostics and engine management can be used to optimize the catalytic process, reduce NOx and NH₃ emission, increase catalyser life span and reduce urea injection.

Truck Emission Control: Compliance with 2005 (Euro IV) and 2008 (Euro V) emission standards for heavy-duty trucks will require exhaust after-treatment. Selective Catalytic Reduction (SCR) to reduce NO_x emission has been adopted for mid- and heavy-duty trucks by several major manufacturers. In order to optimize performance and to reduce cost, the ammonia slip related to the necessary urea solution injection may need to be monitored, as NH₃ levels in transient regimes reach up to 50 ppm.

Axetris LGD advantages:

• 190° hot-gas measurement
• Compensated for high moisture
• High NH₃ selectivity
• Low ppm-level detectivity.

Agriculture and Livestock Farming
Most ammonia emissions result from metabolic activities related to bacteria in livestock farming of poultry, cattle and pigs. Ventilation in the stables must be managed in order to avoid long-term over-critical exposure of the animals to ammonia, causing stress, pour health and reduced productivity. In poorly ventilated stables the health of the personnel also can be endangered. At the same time, ventilation and heating must be minimized/optimized to safe energy while keeping temperatures at an adequate level, especially when young livestock is present. Regulations in the EU are pushing toward a reduction of NH₃ emissions from livestock operations and scrubbing in washers must be monitored. Fertilization in intensive agriculture is another source of ammonia.

Axetris LGD advantages:

• No ageing or degradation
• Calibration-free
• High NH₃ selectivity
• Low ppm-level detectivity

Industrial Applications
Refrigeration: Due to its interesting thermo-dynamic properties ammonia has been used for decades in industrial style refrigeration. Apart from its toxic properties in case of an accidental release, it is considered to be efficient, economical and environmentally friendly because it does not deplete the ozone layer or contribute to global warming, which is not the case for most other refrigerants.

Applications include:

• Cold storage
• Food manufacturing, processing & preservation
• Beverage production Ice rinks

Chemical Industry:Today’s ammonia production of more than 100 million tons per year principally uses hydrocarbons as an educt in a catalyzed process. Applications include:

• Fertilizer production (more than 80% of the produced ammonia)
• Explosives production
• Plastic manufacturing
• Pharmaceutical products.

Axetris LGD advantages:

• Calibration-free
• Continous sensor status monitoring
• High NH3 selectivity
• Low ppm-level detectivity

“Axetris allows system integrators to access innovative laser gas detection technology”

Axetris’ LGD gas sensors are stand-alone, ready-to-use OEM subsystems for selective detection and monitoring of gases. The sensor is based on a technology called “TDLS” – or Tunable Diode Laser Spectrometry, which has proven its validity in high-end laboratory and process control applications. It uses a laser to scan the specific absorption lines of a target gas with an extremely high resolution, which enables a precise measurement of the gas concentration without any cross-sensitivity. Axetris’ proprietary approach to TDLS leverages this technology to low-cost, high-volume gas detection & monitoring applications: The use of low-cost telecom-type laser diodes as light source, combined with Axetris’ intellectual property of reference channel-free devices, reduces the gas sensor to a set of generic components and enables significant cost synergies across applications.

The LGD gas sensor technology brings a competitive solution to most of the drawbacks of current sensors:

• Extremely high selectivity to the target gas
• Functional safety, continuous status reporting
• Long lifetime (10+ years)
• Fast response times
• Low power consumption possible
• Very low cost-of-ownership (no regular replacement and/or calibration)
• Low cost of the gas sensor through excellent scaling costs of the components

The following shows typical test data of the LGD Ammonia Sensor in terms of detection limit, repeatability, drift and stability against temperature variations for an operation between -40°C and +40°C, and 0 to 1,000 ppm NH₃.

For a better control of the set concentration values, the LGD Ammonia Sensor was operated in a “flow-through” configuration.

The span data shows high linearity over the entire range of concentration, and the calibration is highly stable after 11 weeks of operation.

Detection Limit
The low RMS noise of 150 ppb gives an accuracy of 300 ppb, and a detection limit of 500 ppb at 3s, or a detection limit of 1 ppm at 6s.

Repeatability
The figure below shows a perfect repeatability test for set NH3 concentration values of 0 ppm, 5 ppm, 10 ppm, 20 ppm, 50 ppm, 70 ppm and 100 ppm.

Stability & Temperature Drift
Short-term stability (80 minutes) at 20 ppm yields a reading of (20.1  +/-0.45) ppm, corresponding to an extremely low RMS noise of 0.15 ppm.

The zero-concentration temperature drift (13.5 hours, see insert in above figure) was recorded under a variation of ambient temperature from +40°C to -40°C, yielding a reading of (-0.3 +-2.5) ppm, with a RMS noise of only 1 ppm.

High Concentration Temperature Drift
The zero-concentration temperature drift (13.5 hours, see insert in above figure) was recorded under a variation of ambient temperature from +40°C to -40°C, yielding a reading of (-0.3 +/-2.5) ppm, with a RMS noise of only 1 ppm.

Tests on Axetris’ LGD laser diode gas sensor have shown that stable, low ppm range measurements of ammonia are possible. This sensor positions itself as a real alternative to current electrochemical detectors that have serious shortcomings in terms of stability, lifetime, cross-sensitivity and speed.

The LGD NH₃ sensor thus opens a new perspective on applications in agriculture, industrial safety, automotive and medical technology.