Nitrogen dioxide
Nitrogen dioxide is a combustion gas from traffic, gas appliances and industry. Indoors it signals outdoor air pollution coming in — and gas cooking or heating producing it directly. It irritates the airways and is a recognised marker of overall air quality near busy roads.
The marker for traffic and combustion.
NO₂ tells you how much outdoor combustion pollution reaches your indoor air — and whether gas appliances are adding to it.
Respiratory effects
NO₂ inflames airways, worsens asthma and increases respiratory infections — children and people with lung conditions are most affected.
Outdoor-air marker
Indoor NO₂ closely tracks nearby traffic. It shows when and how much road pollution is entering the building.
Gas appliances
Gas hobs, ovens and unflued heaters emit NO₂ directly — a frequent, overlooked indoor source.
Compliance
WHO tightened NO₂ guidelines in 2021. Continuous data shows whether your indoor air meets them.
Lower than you might expect.
The WHO sharply tightened NO₂ guidance in 2021 to 25 µg/m³ over 24 hours. Healthy interiors aim below it; spikes usually mean traffic or gas combustion.
Combustion, indoors and out.
NO₂ is produced wherever fuel burns hot — so its indoor level reflects both the street outside and the appliances inside.
Road traffic
Vehicle exhaust is the dominant outdoor source. Buildings near busy roads see NO₂ enter with ventilation and infiltration.
Gas appliances
Gas cooking and unflued heaters release NO₂ straight into the room, often the highest indoor peaks.
Industry & generators
Nearby combustion plant, boilers and generators add to the outdoor background that seeps in.
Outdoor-air timing
Rush-hour peaks outside translate into indoor peaks; data helps time ventilation to cleaner periods.