Environmental pollution due to nitrogen compounds

Application Note16 Oct 2023

Nitrogen (N2) is the basis of all life and the total amount present on earth always remains the same. It is found in the air, water and soil and is an elementary component of humans, animals and plants. You can read why nitrogen can still be a problem in this blog post.

Author: Rui Protasio, Product Manager Laser Gas Detection, Axetris Switzerland

Nitrogen compounds can pose a threat to the environment and climate. However, this is not due to elemental nitrogen in the air, but to reactive nitrogen that combines with other substances. There are only a few natural processes and bacteria that can produce reactive nitrogen. However, reactive nitrogen generated by human activities has been increasing massively since the mid-19th century. Today, the permissible limits for reactive nitrogen compounds are exceeded around fourfold.

The conversion of N2 in the nitrogen cycle

Depending on the country, up to 70% of these reactive nitrogen compounds originate from agriculture. Both industrially-produced fertilisers and manure contain ammonia and ammonium compounds. They react with water in the soil to form ammonium ions, which are further processed by bacteria and absorbed by plants. In most cases, the use of fertilisers leads to nitrogen overload, since the plants can only absorb a small portion of it. The rest remains as nitrate in soils and waters or is released into the atmosphere as nitrous oxide. Reactive nitrogen compounds can drastically reduce forest ecosystems’ uptake capacity for methane (CH4) and carbon dioxide (CO2) and thus also increase the discharge of other climate-damaging gases.

Air pollutant ammonia

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Ammonia (NH3) released into the air reacts with other pollutants, forming the basis for particulate matter. Impacts on health cannot be ruled out, especially cardiovascular problems and respiratory diseases. Particulate matter is becoming a serious problem, especially with pollutants from exhaust fumes in large cities. But even pure ammonia in the air has negative consequences for the health of humans, animals and entire ecosystems. Ammonia has both a corrosive effect on plants and leads to their overfertilisation (eutrophication) and thus to acidification. In agriculture, increased ammonia concentrations can negatively effect the health of livestock.

Challenges in ammonia monitoring

Reliable and continuous monitoring of ammonia is still proving difficult, as it is a very reactive gas that adsorbs easily to surfaces. It is also often surrounded by a gas matrix, which is usually complex and can lead to interference with other gases. Fortunately, the TDLS technology used in the LGD sensor modules from Axetris has an excellent track record in this area. By using narrow-band laser diodes, the gas absorption lines are selectively scanned, practically ruling out interference with other gases. The innovative LGD Compact NH3 combines this technology with a small, lightweight multi-pass gas cell and active noise reduction on a modulation basis. This also minimises the loss of performance due to contamination. This LGD sensor module is thus perfect for a wide range of ammonia applications where performance and long-term stability are vital. The economic advantages are especially obvious in agriculture because the measurement technology used does not require regular maintenance and calibration.

Environmental protection as a mission

Axetris sensor technology is an established authority in the measurement of industrial emissions and the monitoring of greenhouse gases. With the growing awareness of climate change, the measurement of greenhouse gases in particular has become a mission for Axetris. The first LGD Compact was developed directly for the measurement of methane (CH4). The challenge was reliable detection of even the smallest concentrations in the lowest ppm range. This is particularly important because methane from leaks into the atmosphere quickly becomes highly diluted.

Thanks to the LGD Compact’s optical path length of 80 cm, high sensitivity was achieved with low-cost lasers from the telecommunications sector. This also offers great advantages when measuring ammonia. Ammonia’s odor threshold is already very low and should not permanently exceed 20 ppm on average.

Following the successful introduction of continuous detection for these two gases, development at Axetris is now focusing on the next greenhouse gases. The reduction of reactive nitrogen compounds such as nitrous oxide and nitrogen oxides shows great potential for protecting the climate.