Nitrogen Oxides (NOx)

What is Nitrogen Oxides (NOx)?

Nitrogen oxides (NOx) are a group of gaseous compounds of nitrogen and oxygen — the most important are nitric oxide (NO) and nitrogen dioxide (NO₂). They form during any combustion process involving air, because atmospheric nitrogen reacts with oxygen at high temperatures. NO₂ is identified by WHO and EPA as the main cause of airway inflammation from traffic exhaust.

Why is Nitrogen Oxides (NOx) in cigarettes?

A cigarette's ember reaches about 800 °C — hot enough to make atmospheric nitrogen in the inhaled air react with oxygen to form nitrogen oxides. Add to that nitrogen compounds from the tobacco itself. Each cigarette produces 100 to 300 micrograms of NOx in the mainstream smoke (source: DKFZ). It's exactly the same mixture that comes from diesel exhausts — only significantly more concentrated per breath.

What Nitrogen Oxides (NOx) does to your body — short term

Nitrogen dioxide irritates the lower airways at concentrations already exceeded in busy inner cities. Inhaled, NO₂ reacts with water in the bronchial mucosa to form nitric acid — a direct chemical reaction with tissue. The WHO lowered its annual NO₂ guideline from 40 to 10 µg/m³ in its 2021 Global Air Quality Guidelines, after even small concentrations correlated with elevated asthma incidence in children.

What Nitrogen Oxides (NOx) does long term

Chronic NOx exposure drives inflammatory processes in the lung, promotes asthma, and amplifies the effect of other airway pollutants. In smokers, the effect lands on lungs already damaged by tar and acrolein — a multiplication of harm. Nitrogen oxides also contribute to the formation of peroxynitrite, a highly reactive compound that damages proteins and DNA directly and elevates cardiovascular risk.

How it compares

Germany's workplace exposure limit for nitrogen dioxide is 0.95 mg/m³ (0.5 ppm, DFG MAK 2023). A cigarette sets the NOx concentration in the breathing space to many times this value for a few seconds — inhaled as undiluted smoke directly into the bronchi.

Workplace exposure limit: 0.95 mg/m³ (0.5 ppm NO₂, DFG MAK 2023)