A Brief Guide to NOx Emmissions

July 21, 2022 2 min read


NOx is a generic term for the nitrogen oxides namely nitric oxide (NO) and nitrogen dioxide (NO 2), classified as air pollutants.

NOx formation

NOx can form naturally during a thunderstorm due to extreme heat from lightning and during forest fires. Also produced by living organisms in agricultural fertilization.

However, most of the NOx emitted into the environment is from man-made industrial processes, where the combustion of fossil fuels is present (mobile or stationary processes). The combustion of transportation fuels (engines/vehicles) and industrial combustion processes (power generation/plant boilers) are the main contributors of NOx emissions.

Controlling NOx emissions

NOx reacts with moisture, Ammonia, and other compounds in the air to form Nitric Acid vapour. Therefore, releasing high levels of NOx emissions into the atmosphere has widescale environmental impacts like acid rain formation and contributes to global warming. Humans exposed to excessive NOx emissions are also susceptible to respiratory issues, with prolonged exposure leading to irreversible damage. Asthma sufferers being more susceptible to intense attacks.

According to the World Health Organisation (WHO) 99% of the global population breathe air that exceeds the WHO air quality limits. Seven million deaths globally are attributable to air pollution each year. Therefore, it is vital that policies and investments are made globally to support cleaner transport, energy, and waste management in order to improve the quality of the air

Regulating NOx Emissions

Manufacturers who produce NOx emissions are responsible for ensuring the emissions produced are an acceptable level within the regulations.

Combustion processes are typically regulated in the UK by the Environmental Permitting Regulations (2010). Shortly the Medium Combustion Plant Directive will be written into UK law.

Both of these statutory tools ensure that regular accredited NOx monitoring (and other pollutants such as VOC Emissions) is undertaken on relevant process to quantify emissions (Emission Limit Values) so that they can be better recorded and understood.

Lowering NOx Emissions

Historically secondary solutions such as Selective Catalytic Reduction (SCR) or Selective Non-Catalytic Reduction (SNCR) have been employed to lessen the NOx levels at places like conventional power plants that burn biomasswaste and coal. SCR and SNCR both use ammonia for the conversion of NOx into Nitrogen and water. SCR uses a catalytic bed to accelerate the chemical reaction. Practical constraints however of temperature, time and mixing often lead to worse results in practice.

Emerging oxidation technologies work by using ozone gas, injected directly into the flue, (including dirty flues), to oxidise the NOx into water soluble and reactive Nitrogen Pentoxide (N2O5), combined with an Aqueous Scrubbing System that then absorbs the N2O5. De-NOx systems using combined ozone and scrubbing technologies deliver SCR performance without its limitations.

For companies looking for NOx reduction solutions and support, get in touch with the team at SOS Hygiene.