Measurements · Gases & VOCs
Ozone (O₃)
Also known as ground-level ozone
Ozone: a secondary photochemical pollutant and respiratory irritant, and an occupational hazard near generators.
What it is
What is ground-level ozone (O₃)?
Ozone is a highly reactive form of oxygen. High in the atmosphere it shields the planet from ultraviolet radiation, but at ground level it is a harmful pollutant. Ozone is not emitted directly. It forms when nitrogen oxides and volatile organic compounds react in sunlight, so it is a secondary pollutant that peaks on hot, sunny afternoons and can drift far downwind of the traffic and industry that supplied its precursors. This is why rural and suburban areas sometimes record higher ozone than city centers.
Ozone is one of the six ambient criteria pollutants and a defining component of photochemical smog.
Health and operational effects
Ozone irritates and inflames the airways, reduces lung function, aggravates asthma and other respiratory conditions, and is associated with increased hospital admissions and mortality during high-ozone episodes. Sensitive groups (children, the elderly, outdoor workers, and people with lung disease) feel it first. Beyond human health, ozone damages crops and vegetation, giving it agricultural and ecological significance.
For air-quality agencies, event organizers, and employers with outdoor workforces, ozone forecasting and monitoring drive public alerts and work-rescheduling decisions during summer smog episodes.
Limits
Ozone (O₃) Limit Values
The published values, by averaging period; each links to the standard that sets it.
8-hour
8-hour daily maximum
8-hour peak-season
8-hour TWA (PEL)
A01 Air Quality
Ceiling
Certified emission concentration
One-time test
- WHO 2021 100 µg/m³: 99th percentile (3–4 exceedance days a year)
- WHO 2021 60 µg/m³: mean of the daily maximum 8-hour values over the six consecutive months with the highest ozone
- ACGIH TLV 0.1 ppm: light work; lower for heavier work
- CARB Air Cleaner 0.05 ppm: tested per section 94805; devices sold in California must be certified
Ozone is reported in ppb or µg/m³, and its limits are based on rolling 8-hour averages because health effects track sustained daytime exposure rather than instantaneous peaks. The US EPA NAAQS, WHO 2021 guideline, and WELL standard values appear in the limit table on this page. Interpret ozone as a daytime, warm-season phenomenon: the meaningful comparison is the daily maximum 8-hour average against the standard, and a high reading on a hot afternoon is exactly when action such as public alerts is warranted.
How it is measured
How Ozone (O₃) Is Measured
The reference method is UV photometry: ozone strongly absorbs ultraviolet light at 254 nm, so the analyzer measures how much a UV beam is attenuated by the sample. These instruments are accurate and stable and underpin regulatory networks. For distributed and lower-cost monitoring, electrochemical and metal-oxide sensors give real-time ozone readings but must be compensated for temperature and humidity and for cross-sensitivity with NO₂, with which ozone is chemically entangled. Pairing ozone and NO₂ measurement improves the interpretation of both.
Aethair PRO cartridge1
A pre-calibrated cartridge in one of Aethair PRO's sockets: Aethair O₃+NO₂.
An instrument on Thiamis1
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing ozone sensors
Because ozone forms downwind and peaks in the afternoon, siting is about capturing regional exposure rather than a local source: open locations away from fresh NO emissions (which locally destroy ozone) give representative readings, and roadside sites can paradoxically read low. Mount at breathing height with an unobstructed intake, and record temperature and solar radiation, since both drive ozone formation.
Every device and option that measures Ozone (O₃) 2
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
 Aethair O₃+NO₂ 0d45 | Gas sensor cartridge | Aethair PRO | |
 2B Technologies · POM | Specialty Air Analyzers | Thiamis |
Where it is monitored
Solutions That Monitor Ozone (O₃)
Each one links to the solution page showing what that industry measures it for.
Outdoor Monitoring
Core parameterOzone is a defining component of photochemical smog and one of the six ambient criteria pollutants, but because it forms downwind in sunlight rather than being emitted directly, it demands its own careful monitoring across a network.
Indoor Air Quality
Often addedOffices, schools, homes, and public buildings
School Air Monitoring
Often addedClassroom CO₂, particulates, and campus IAQ
Wildfire Air Monitoring
Often addedSmoke plumes, black carbon, and community exposure
Article Library
Reading on Ozone (O₃)
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.
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.
How Building Certifications Use Air Quality Monitoring
How WELL and LEED v5 incorporate air quality monitoring, why both frameworks are moving toward continuous performance, and what that means for building teams.
Fenceline Air Quality Monitoring: Equipment and Approaches
Compare fenceline air quality monitoring approaches: standalone stations, pelican-case kits, and connected 4G sensor networks.
Related
More in Gases & VOCs
Questions
Ozone (O₃) FAQ
Why is ozone worse in the suburbs than in the city?
Ozone is a secondary pollutant that forms downwind as precursors react in sunlight, and fresh nitric oxide emissions near busy roads actually destroy it locally. So city-center roadside sites can read lower than suburban and rural areas that receive the aged, ozone-rich air, a well-known feature of the chemistry.
When is ground-level ozone highest?
On hot, sunny afternoons in the warm season, because sunlight and heat drive its formation from NOₓ and VOC precursors. Ozone is essentially a daytime, summer phenomenon, which is why its limits use daily maximum 8-hour averages and why alerts are issued during heatwaves.
Can a low-cost sensor measure ozone accurately?
Low-cost electrochemical and metal-oxide sensors give useful real-time ozone trends but need temperature/humidity compensation and correction for cross-sensitivity with NO₂. For regulatory purposes, UV photometry is the reference method; low-cost sensors are best co-located against one.
How do I monitor ozone?
Pair a Thiamis gateway with a dedicated ozone monitor (UV photometric or electrochemical). Use the configurator to combine ozone with NO₂ and the other criteria pollutants for a complete ambient or smart-city air-quality station.
Monitor Ozone (O₃) on the Record
Schedule a callConfigure Ozone (O₃) Monitoring All parameters
A 30-minute call: you tell us about your application, then we demo the solution for it.