NO₂: nitrogen dioxide and the airways

A gas produced by combustion

Nitrogen dioxide is a reactive gas associated with fuel combustion. Road traffic and other combustion sources can contribute outdoors, while combustion appliances can contribute indoors. A reading alone does not identify the particular source responsible at a location, and NO₂ is not a measurement of particle concentration.

Why it matters for breathing

EPA describes irritation of the respiratory system and worsening of respiratory disease, particularly asthma, after breathing air with elevated NO₂. Children and people with asthma are among more susceptible groups. These public-health statements describe a hazard; they do not diagnose an individual effect from one app reading.

Check the unit and the period

NO₂ may be reported in µg/m³ or ppb, which are not interchangeable numbers. Conversion requires specified conditions. WHO recommendations, legal limits and AQI categories serve different purposes and can use different averaging periods. An hourly concentration does not establish a daily or annual average.

Match the next step to the situation

Use the advisory for the reported pollutant and local index when planning prolonged or strenuous activity. Follow an existing asthma action plan where relevant. Do not assume a particle-filtering mask protects against NO₂, or that outdoor data establish the air quality inside a building.

Sources

Educational information; personal health questions belong with your clinician.

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