Indoor environment factor · measured in µg/m³ or ppb (1 ppb ≈ 1.9 µg/m³)
Nitrogen dioxide (NO₂)
Part of: Nitrogen oxides (NOₓ)
Also: NO2, NO₂
A reddish-brown, irritant gas formed when fuel burns at high temperature. Indoors it comes chiefly from gas cooking and unvented gas or kerosene heaters; outdoors from traffic. It inflames the airways and is linked to childhood asthma.
Why it matters indoors
Nitrogen dioxide belongs to the nitrogen oxides produced in any hot flame. Indoors, a gas hob without an extractor hood can raise kitchen concentrations well above outdoor levels within minutes of cooking; unvented gas or paraffin heaters do the same in living rooms. It is also the traffic pollutant that most readily infiltrates buildings near busy roads.
Where it comes from indoors
Gas cooking and gas ovens, unflued gas and kerosene heaters, tobacco smoke, and infiltration of outdoor air near traffic.
Health effects
Airway inflammation, increased asthma symptoms and hospital admissions, reduced lung function growth in children, and higher susceptibility to respiratory infections. Children in homes with gas cooking show measurably more respiratory symptoms.
Exposure limits
| Jurisdiction | Value | Averaging time | Source |
|---|---|---|---|
| World Health Organization | 10 µg/m³ | annual | WHO AQG 2021 |
| World Health Organization | 25 µg/m³ | 24 hours | WHO AQG 2021 |
| World Health Organization (indoor) | 200 µg/m³ | 1 hour | WHO indoor air quality guidelines 2010 |
| European Union (ambient) | 20 µg/m³ annual · 200 µg/m³ 1 hour | from 2030 | Directive (EU) 2024/2881 |
Slovak, UAE and Hong Kong values are being compiled in the indoor air quality limits table.
How it is measured
Chemiluminescence analysers are the reference; electrochemical sensors track it continuously; passive diffusion tubes give weekly averages cheaply.
What the studies report
12 of 66 Findings — those with the strongest study design.
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| Biomass fuel | mean 63.84 | — · home | review of studies of indoor air pollution in Ethiopian households with calculated mean concentrations across the included studies: particulate matter, nitrogen dioxide, total volatile organic compounds, polycyclic aromatic hydrocarbons and carbon monoxide, by geography, stove type and household activity | F-1001 Asefa Human exposure to indoor air pollution in Ethiopian househol… (2022) | machine |
| Atopic dermatitis (eczema) | OR 1.30 (1.04–1.61) per 10 | adults | systematic review and meta-analysis (20 studies) | F-0002 The relationship between outdoor air pollutants and atopic d… (2022) | person |
| Air purifiers | difference 36 | low-income households with gas stoves · dwelling | intervention study in low-income homes with gas stoves in Lowell, Massachusetts: indoor NO2 and PM2.5 with stove use, temperature and humidity measured over 5-7 days per month, HEPA/carbon filter air purifiers introduced after the fourth month, linear mixed models with homes as random effects | F-0669 Kadiri et al. Effectiveness of HEPA/Carbon Filter Air Purifier in Reducing… (2025) | machine |
| — | mean 30.0 | inner-city children aged 2-6 years with asthma · child's bedroom | longitudinal study of 150 inner-city children aged 2-6 years with physician-diagnosed asthma in Baltimore: indoor air monitored for 72 hours in the child's bedroom at baseline, 3 and 6 months, caregiver questionnaire on asthma symptoms in the previous two weeks and health care use | F-0671 Bishop A Longitudinal Study of Indoor Nitrogen Dioxide Levels and R… (2008) | machine |
| Gas stoves | mean 33.1 | inner-city children aged 2-6 years with asthma · child's bedroom | longitudinal study of 150 inner-city children aged 2-6 years with physician-diagnosed asthma in Baltimore: indoor air monitored for 72 hours in the child's bedroom at baseline, 3 and 6 months, caregiver questionnaire on asthma symptoms in the previous two weeks and health care use | F-0672 Bishop A Longitudinal Study of Indoor Nitrogen Dioxide Levels and R… (2008) | machine |
| — | mean 16.8 | inner-city children aged 2-6 years with asthma · child's bedroom | longitudinal study of 150 inner-city children aged 2-6 years with physician-diagnosed asthma in Baltimore: indoor air monitored for 72 hours in the child's bedroom at baseline, 3 and 6 months, caregiver questionnaire on asthma symptoms in the previous two weeks and health care use | F-0673 Bishop A Longitudinal Study of Indoor Nitrogen Dioxide Levels and R… (2008) | machine |
| Asthma | OR 1.00 (0.93–1.07) per 20 ppb | inner-city children aged 2-6 years with asthma · child's bedroom | longitudinal study of 150 inner-city children aged 2-6 years with physician-diagnosed asthma in Baltimore: indoor air monitored for 72 hours in the child's bedroom at baseline, 3 and 6 months, caregiver questionnaire on asthma symptoms in the previous two weeks and health care use | F-0674 Bishop A Longitudinal Study of Indoor Nitrogen Dioxide Levels and R… (2008) | machine |
| Hospitalisation | OR 1.13 (0.69–1.09) per 20 ppb | inner-city children aged 2-6 years with asthma · child's bedroom | longitudinal study of 150 inner-city children aged 2-6 years with physician-diagnosed asthma in Baltimore: indoor air monitored for 72 hours in the child's bedroom at baseline, 3 and 6 months, caregiver questionnaire on asthma symptoms in the previous two weeks and health care use | F-0675 Bishop A Longitudinal Study of Indoor Nitrogen Dioxide Levels and R… (2008) | machine |
| Range hoods and kitchen exhaust | difference 12.7 | children's households with gas stoves · kitchen | pilot before-after trial in 14 homes with gas stoves and children: a video-based educational intervention on cooking ventilation plus range hood replacement where needed, with real-time NO2 and PM2.5 during cooking events and passive NO2 samplers over the pre- and post-intervention intervals | F-0676 Holm Measured air quality impacts after teaching parents about co… (2025) | machine |
| Range hoods and kitchen exhaust | difference 470 | children's households with gas stoves · kitchen | pilot before-after trial in 14 homes with gas stoves and children: a video-based educational intervention on cooking ventilation plus range hood replacement where needed, with real-time NO2 and PM2.5 during cooking events and passive NO2 samplers over the pre- and post-intervention intervals | F-0677 Holm Measured air quality impacts after teaching parents about co… (2025) | machine |
| Range hoods and kitchen exhaust | difference 1.0 | children's households with gas stoves · kitchen | pilot before-after trial in 14 homes with gas stoves and children: a video-based educational intervention on cooking ventilation plus range hood replacement where needed, with real-time NO2 and PM2.5 during cooking events and passive NO2 samplers over the pre- and post-intervention intervals | F-0678 Holm Measured air quality impacts after teaching parents about co… (2025) | machine |
| Unvented heaters | ratio 1.8 (1.6–2.1) | school children · classroom | double-blind, cluster-randomised crossover trial in Australian school classrooms: low-NOx unflued gas heaters against non-indoor-emitting flued gas heaters, NO2 and formaldehyde measured with passive diffusion badges, children recorded symptoms, medication use and lung function twice daily | F-0689 Respiratory Health Effects of Exposure to Low-NOx Unflued Ga… (2010) | machine |
Each row is one Finding — a sentence as printed in one study, recorded with its page in the Coridum Knowledge Base. Follow the Finding number for the exact wording and the citation. Checked says who verified the row: machine means every automatic check passed and the surrounding text was read; person means someone read the sentence in the document. The studies are curated in the Coridum Knowledge Base; the reading of them together is a Claim, shown separately.
How strong is the evidence
-
In adults, long-term exposure to nitrogen dioxide (NO₂) is associated with newly diagnosed atopic dermatitis.
A Claim is Coridum reading the Findings together, not a quotation from one study — according to Coridum. The grade follows the study designs behind it: A is the strongest, D means a single study or a mechanism.
Identifiers
- Molecular formula
- NO₂
- IUPAC name
- nitrogen dioxide
- CAS Registry Number
- 10102-44-0 · PubChem · CTD
- InChIKey
- JCXJVPUVTGWSNB-UHFFFAOYSA-N
- MeSH
- D009585
- SMILES
[N+](=O)[O-]
In the literature
- The influence of photochemistry on outdoor to indoor NO2 in some European museums… (2022). Indoor air. doi:10.1111/ina.12999 CKB 0059
- Kadiri et al. Effectiveness of HEPA/Carbon Filter Air Purifier in Reducing Indoor NO2 and PM2.5 in Homes with Gas Stove Use in Lowell, Massachusetts (2025). Toxics. doi:10.3390/toxics13121030 CKB 1189
- A cohort study of the multipollutant effects of PM2.5, NO2, and O3 on C-reactive protein…. Environmental Epidemiology. doi:10.1097/ee9.0000000000000308 CKB 0694
Studies in the Coridum Knowledge Base in which this term is used. The definition follows standard usage in WHO, ISO and textbook sources; it is not quoted from these papers.
CKB = document number in the Coridum Knowledge Base, our curated library of peer-reviewed studies. Follow the DOI for the original paper.
Cite this page
Coridum Research. Nitrogen dioxide (NO₂). Coridum Knowledge G-0048, 16 September 2026. https://coridum.com/k/G-0048/