Measurements · Gases & VOCs
Nitrogen Dioxide (NO₂)
Nitrogen dioxide: a criteria pollutant, respiratory irritant, and marker of traffic combustion.
What it is
What is nitrogen dioxide (NO₂)?
Nitrogen dioxide is a reddish-brown gas with a sharp odor, one of the family of nitrogen oxides (NOₓ) produced whenever fuel is burned at high temperature. Its dominant source is traffic (diesel engines in particular), along with power generation, industrial combustion, and, indoors, unvented gas cooking and heating. Because road transport is the main driver, NO₂ is a strong marker of combustion near roads and in cities, with concentrations that fall sharply just meters from a busy road.
It is one of the six criteria pollutants tracked in ambient air quality networks worldwide.
Health and operational effects
NO₂ inflames the airways, reduces lung function, and worsens asthma and respiratory infection; long-term exposure is associated with the development of asthma in children and with cardiovascular and respiratory mortality. It also acts as a precursor: in the atmosphere it drives the formation of ozone and of secondary particulate matter, so controlling NO₂ yields benefits beyond the gas itself.
For cities, schools near busy roads, and workplaces with combustion sources, NO₂ is both a public-health metric and a regulatory one, sitting under EPA, WHO, and EU limit values that increasingly shape low-emission zones and planning decisions.
Limits
Nitrogen Dioxide (NO₂) Limit Values
The published values, by averaging period; each links to the standard that sets it.
24-hour
8-hour TWA
1-hour
One-time test
- EU 2024/2881 20 µg/m³: 2030 limit value (previously 40)
- LEED v5 21 ppb: 40 µg/m³
NO₂ is reported in ppb or µg/m³. Compare annual averages against annual limits and 1-hour values against short-term ones: the US EPA NAAQS, the WHO 2021 guideline (which lowered the annual value substantially), and the EU 2030 limit values all appear in the limit table on this page. Roadside peaks during rush hour are expected. The compliance question is whether the relevant averaged value exceeds its limit.
How it is measured
How Nitrogen Dioxide (NO₂) Is Measured
Reference-grade ambient monitoring uses chemiluminescence analyzers, which measure the light emitted when NO reacts with ozone and infer NO₂ by difference. For distributed networks and lower-cost monitoring, electrochemical sensors produce a current proportional to NO₂ concentration; they are compact and real-time but require compensation for temperature, humidity, and cross-sensitivity to other gases such as ozone. Because NO₂ and ozone interfere with one another, monitors are often deployed as a pair, and low-cost sensors benefit from co-location against a reference for correction.
Aethair PRO cartridges3
A pre-calibrated cartridge in one of Aethair PRO's sockets: Aethair NO₂, Aethair MultiSense, and Aethair O₃+NO₂.
An instrument on Thiamis2
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing NO₂ sensors
For traffic and ambient monitoring, place sensors at the roadside or site boundary at breathing height, with an intake clear of obstructions, and record wind speed and direction to relate concentrations to traffic and sources. Indoors, monitor near unvented combustion appliances such as gas stoves. Because NO₂ gradients are steep near roads, sensor position relative to the traffic source strongly affects the reading, so consistency of placement matters for trends.
Every device and option that measures Nitrogen Dioxide (NO₂) 5
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
 Aethair NO₂ 0d05 | Gas sensor cartridge | Aethair PRO | Nitrogen Dioxide (NO₂)Dew PointHeat IndexRelative HumidityIlluminance / LightParticle Count (by size)PM1 |
 Aethair MultiSense 0d09 | MultiSense cartridge | Aethair PRO | |
 Aethair O₃+NO₂ 0d45 | Gas sensor cartridge | Aethair PRO | |
 RAE · MultiRAE Lite, MultiRAE, MultiRAE Pro… | Gas Detectors | Thiamis | |
 Trolex · Sentro X (TX6310) | Gas Detectors | Thiamis |
Where it is monitored
Solutions That Monitor Nitrogen Dioxide (NO₂)
Each one links to the solution page showing what that industry measures it for.
Outdoor Monitoring
Core parameterNitrogen dioxide is the ambient pollutant most closely tied to traffic, with concentrations that fall sharply just meters from a busy road.
Cabin Air Quality
Often addedRespirable dust, gases, and blast monitoring
Indoor Air Quality
Often addedOffices, schools, homes, and public buildings
Occupational Safety & Industrial Hygiene
Often addedWorker exposure, confined space, and heat stress
Oil & Gas / Petrochemical
Often addedFence-line VOC, H₂S, and methane leak detection
Perimeter Monitoring
Often addedSite boundary dust, silica, and noise compliance
Article Library
Reading on Nitrogen Dioxide (NO₂)
Ozone Exposure Limits and Monitoring: OSHA and NAAQS
OSHA's ozone PEL is 0.1 ppm as an 8-hour TWA. How NIOSH, ACGIH, and the 70 ppb NAAQS compare, and why ozone needs short-interval monitoring.
OSHA Air Quality Standards 2026: PELs & 29 CFR 1910.1000
OSHA air quality standards for indoor and outdoor work: permissible exposure limits, Table Z-1, 29 CFR 1910.1000, and the heat and wildfire smoke triggers.
Air Quality Near Data Centers: What Communities Should Know
Air quality near data centers: construction dust, diesel generator emissions, and noise, and how communities get independent monitoring data.
Data Center Air Quality Monitoring, Inside and Out
Data center air quality monitoring for operators: ISO 14644 cleanliness in the white space, construction dust, generator emissions, and perimeter noise.
Wildfire Smoke Air Quality Monitoring: Detection & Response
Wildfire smoke monitoring for EHS and public health teams: real-time PM2.5, the AQI 151 respirator trigger, and how to alert workers before smoke arrives.
Ambient Air Quality Monitoring: What Nonattainment Changes
Ambient air quality monitoring explained: how PM2.5 attainment is measured, what a nonattainment designation triggers, and what site-level monitoring adds.
Related
More in Gases & VOCs
Questions
Nitrogen Dioxide (NO₂) FAQ
Where does indoor NO₂ come from?
Indoors, the main source is unvented combustion: gas cooktops and ovens, gas or kerosene heaters. Cooking on a gas stove without a range hood can push kitchen NO₂ well above outdoor levels, which is why ventilation over gas appliances matters and why monitoring is useful in homes and commercial kitchens.
Why are NO₂ and ozone measured together?
The two are chemically linked: NO₂ helps form ozone in sunlight, and they cross-interfere in many sensors. Measuring them together gives a truer picture of the photochemical smog system and allows sensor readings to be corrected for the interference.
What is the limit for NO₂?
Limits vary by framework: the US EPA NAAQS, the WHO 2021 guideline, and the EU 2024 directive (with 2030 limit values) each set annual and short-term values, listed with their averaging periods in the limit table on this page. The WHO annual guideline is the strictest and was lowered sharply in 2021.
How do I monitor NO₂?
Aethair PRO measures NO₂ with a gas sensor cartridge, or Thiamis can connect an electrochemical multi-gas monitor or a dedicated NO₂ analyzer. For regulatory networks, reference chemiluminescence methods apply. Use the configurator to combine NO₂ with the other criteria pollutants for an ambient or roadside air-quality station.
Monitor Nitrogen Dioxide (NO₂) on the Record
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