Nitrogen Oxides (NO)

UNICERT is the leading inspection body in the area of Air Quality test for Nitric Oxide (NO) and objectives to reduce environmental emission/pollution and enhance environmental performance to the society.

Nitric oxide (NO):

Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula NO. It is one of the principal oxides of nitrogen. Nitric oxide is a free radical, i.e., it has an unpaired electron, which is sometimes denoted by a dot in its chemical formula, i.e., ·NO. Nitric oxide is also a heteronuclear diatomic molecule, a historic class that drew researches which spawned early modern theories of chemical bonding.

An important intermediate in chemical industry, nitric oxide forms in combustion systems and can be generated by lightning in thunderstorms. In mammals, including humans, nitric oxide is a signaling molecule in many physiological and pathological processes. It was proclaimed the “Molecule of the Year” in 1992. The 1998 Nobel Prize in Physiology or Medicine was awarded for discovering nitric oxide’s role as a cardiovascular signaling molecule.


Effects of Nitric oxide (NO) on human health:

NOx mainly impacts on respiratory conditions causing inflammation of the airways at high levels. Long term exposure can decrease lung function, increase the risk of respiratory conditions and increases the response to allergens. NOx also contributes to the formation of fine particles (PM) and ground level ozone, both of which are associated with adverse health effects.

NO exerts crucial roles in vascular and neuronal signal transduction, smooth muscle contractility, bioenergetics, platelet adhesion and aggregation, immunity, and cell death regulation. The evidence accumulated over the last 25 years suggests that a defective control of the NO levels causes pathologies, such as hypertension, cardiovascular dysfunctions, neurodegeneration, arthritis, asthma and septic shock.


Environmental effects of Nitric oxide (NO):

Acid deposition

Nitric oxide reacts with the hydroperoxy radical (HO2•) to form nitrogen dioxide (NO2), which then can react with a hydroxyl radical (•OH) to produce nitric acid (HNO3):

Nitric acid along with sulfuric acid, contribute acid rain deposition.


Ozone depletion

Furthermore, ·NO participates in ozone layer depletion. In this process, nitric oxide reacts with stratospheric ozone to form O2 and nitrogen dioxide:

As seen in the Concentration Measurement section, this reaction is also utilized to measure concentrations of ·NO in control volumes.


Precursor to NO2

As seen in the Acid deposition section, nitric oxide can transform into nitrogen dioxide (this can happen with the hydroperoxy radical, HO2•, or diatomic oxygen, O2). Symptoms of short-term nitrogen dioxide exposure include nausea, dyspnea and headache. Long-term effects could include impaired immune and respiratory function.


Occupational safety and health:

In the U.S., the Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for nitric oxide exposure in the workplace as 25 ppm (30 mg/m3) over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 25 ppm (30 mg/m3) over an 8-hour workday. At levels of 100 ppm, nitric oxide is immediately dangerous to life and health.


Interested Parties including Regulatory Authorities:

  1. Persons affected by NO
  2. Industries, Laboratories using/ Generating NO
  3. Warehouses Containing Chemicals of NO
  4. Motor Vehicles for personal and commercial uses
  5. Private / Govt. Projects to control NO
  6. Handling and transportation of chemical containing NO
  7. Local Environmental Department/ Authorities
  8. Local Government Authorities like Municipalities, City Corporation etc.
  9. Local Law Enforcing Agencies like Police, Magistrate and Regulatory Authorities etc.


Benefit of Monitoring:

By monitoring long-term contamination trends, every country establishes baseline contamination levels, making it possible for early identification of contamination events. Daily events and long term trends are captured and taken step to reduce environmental emission/ pollution and enhance environmental performance of the society.