Ozone in air measurement
Ozone in Air Analyser: Eco Sensors UV-100
Measuring ozone in air means determining the concentration of ozone gas (O3) in a sample of air, usually in parts per million (ppm) or parts per billion (ppb) by volume. The most accurate way to do it is UV photometry: ozone absorbs ultraviolet light at 254 nm, so the amount of light absorbed tells you exactly how much ozone is present.
The Eco Sensors UV-100 is a compact UV photometric ozone analyser that reads from 0.01 to 999 ppm with 2% accuracy. It logs data, drives 4–20 mA and 0–2.5 V outputs, and warns you when ozone at the sample point is above 0.1 ppm. Ecotao supplies it across South Africa and neighbouring countries.
- 0.01–999 ppmRange, in three sub-ranges
- 2%Accuracy
- 10 sSampling time
- 254 nm UVSame principle as the SA reference method
What is ozone in air, and why measure it?
Ozone (O3) is a highly reactive form of oxygen. It is a strong oxidant, which makes it useful for disinfection, odour control and water treatment. The same property makes it a respiratory irritant, so concentrations in occupied spaces have to be kept low and checked.
Where ozone in air comes from
- Ozone generators (corona discharge and UV types) used for water treatment, food processing, cold-room sanitation and odour removal.
- Ozone leaks from pipework, contact tanks and off-gas destruct units in treatment plants.
- Electrical and UV equipment such as high-voltage discharge, some welding processes and 185 nm UV lamps.
- Photochemical smog, where sunlight drives reactions between nitrogen oxides and volatile organic compounds outdoors.
Why measure it
- Worker safety: confirm exposure stays below the South African occupational limits (see limits table).
- Process control: hold a target ozone concentration in a treatment chamber, test cabinet or room-disinfection cycle.
- Re-entry checks: confirm a room or cold store is safe after ozone treatment.
- Reference checks: verify the readings of lower-cost electrochemical or metal-oxide ozone monitors.
Units at a glance: 1 ppm = 1,000 ppb. At 25 °C and 101.3 kPa, 1 ppb of ozone ≈ 1.96 µg/m³, so 0.1 ppm ≈ 196 µg/m³ (0.2 mg/m³) and South Africa's ambient standard of 120 µg/m³ equals 61 ppb.
How a UV photometric ozone analyser works
Ozone has a very strong absorption band in the ultraviolet, peaking close to the 253.7 nm emission line of a low-pressure mercury lamp. A UV photometer uses that fact to count ozone molecules directly, rather than inferring them from a chemical reaction.
- Sample: air is drawn from the measuring point through tubing and a filter into an optical cell.
- Absorb: a 254 nm mercury lamp shines through the cell. Ozone in the sample absorbs part of that UV light.
- Detect: a UV detector measures how much light gets through. More ozone means less light.
- Calculate: the Beer–Lambert law converts light absorption to concentration. Temperature and pressure in the cell are measured and corrected for, so the result is reported accurately in ppm (v/v).
Because the measurement depends on a physical property of the ozone molecule, UV photometry is stable and largely free of the cross-sensitivity to chlorine, nitrogen dioxide and humidity that affects chemical sensors. This is why South Africa's National Ambient Air Quality Standards specify the UV photometric method (SANS 13964) as the reference method for ozone.
Eco Sensors UV-100 ozone analyser
UV-100: laboratory-grade ozone measurement in a 2.1 kg instrument
The UV-100 brings the measurement principle used in reference-grade ozone monitors into a benchtop instrument you can carry between sites. It reads ozone in air from 0.01 ppm, low enough to check workplace exposure against the 0.1 ppm limit, up to 999 ppm for ozone treatment chambers and diluted process gas. Readings update every 10 seconds.
Three selectable ranges (0–1.00 ppm, 0–10.0 ppm and 0–999 ppm) let you match the display resolution to the job. Internal temperature and pressure sensors correct the reading automatically, which matters for accurate results at altitude on the Highveld. Each instrument is calibrated against a reference instrument with NIST-traceable calibration, and the calibration data and date are included in its document pack.
- Built-in data logger downloads over USB or serial as a time- and date-stamped record, for trend analysis and audit trails.
- 4–20 mA and 0–2.5 VDC outputs connect to a PLC, SCADA system, chart recorder or ozone generator control loop.
- Four status LEDs show power on, recalibration due, sample filter change due, and ozone above 0.1 ppm at the sample point.
- Portable or fixed: runs on an AC adapter or a 12 V external battery (12 VDC at 400 mA), so it works in the lab, on a plant walkdown or in a vehicle.
- Compact: 95 × 210 × 216 mm and 2.1 kg, with a ¼" compression fitting for the sample inlet.
What the UV-100 does in each application
Water and wastewater treatment
Monitors ozone leaking into generator rooms and around contact tanks, and checks that off-gas destruct units are working. The 4–20 mA output can drive an alarm or ventilation interlock.
Room and cold-store disinfection
Confirms the target ozone dose was reached during a treatment cycle, then confirms levels have fallen below 0.1 ppm before staff re-enter. The log provides a record of each cycle.
Food and agriculture
Measures ozone in fruit stores, packhouses and grain fumigation enclosures, where too little ozone fails to control mould and too much damages produce and equipment.
Laboratory and research
Gives accurate, repeatable concentration data for oxidation experiments, material ageing tests and university air chemistry studies, without the drift of chemical sensors.
Checking other ozone monitors
Acts as a reference when bump-testing electrochemical or metal-oxide ozone monitors, showing whether a fixed alarm still reads correctly after months in service.
Occupational hygiene surveys
Maps ozone around photocopier rooms, UV curing lines, welding bays and high-voltage equipment, with data that supports an exposure assessment against the SA limits.
UV-100 specifications
← Scroll to see full table →
| Specification | UV-100 |
|---|---|
| Measurement principle | UV absorption photometry |
| UV source | 254 nm mercury lamp |
| Measuring range | 0.01–999 ppm (v/v) |
| Selectable ranges | 0–1.00 ppm, 0–10.0 ppm, 0–999 ppm |
| Accuracy | 2% |
| Sampling time | 10 seconds |
| Compensation | Internal temperature and pressure correction |
| Outputs | Digital display, 0–2.5 VDC, 4–20 mA, USB / serial data |
| Data logging | Built-in, time- and date-stamped |
| LED indicators | On/off, recalibrate, change filter, >0.1 ppm at sample area |
| Sample inlet | ¼" compression fitting |
| Warm-up | At least 30 minutes; over 1 hour preferred for best accuracy |
| Power | 12 VDC at 400 mA (AC adapter or 12 V external battery) |
| Dimensions | 95 × 210 × 216 mm (3.75 × 8.25 × 8.50 in) |
| Weight | 2.1 kg (4.7 lb) |
| Calibration | Against a reference instrument with NIST-traceable calibration; certificate data supplied |
| Warranty | One year |
Using it in cold or humid conditions: where the sample air is cold and condensing, such as a cold store, use extended sample tubing and a moisture trap so water doesn't condense in the optical cell.
How to choose an ozone in air instrument
Three sensing technologies are used to measure ozone in air. The right one depends on how accurate the result must be, what concentration you expect, and whether you need a spot reading, a record or an automatic alarm.
← Scroll to see full table →
| Factor | UV photometric analyser (e.g. UV-100) | Electrochemical sensor | Heated metal-oxide (HMOS) sensor |
|---|---|---|---|
| How it senses ozone | Absorption of 254 nm UV light by ozone molecules | Chemical reaction at an electrode produces a current | Ozone changes the electrical resistance of a heated oxide film |
| Accuracy and stability | Highest; no sensor consumption | Good when freshly calibrated; drifts as the cell ages | Moderate; affected by humidity and temperature |
| Cross-sensitivity | Low; few other gases absorb at 254 nm in normal air | Responds to other oxidants such as chlorine and nitrogen dioxide | Can respond to humidity changes and some VOCs |
| Typical role | Reference readings, lab work, process control, checking other monitors | Handheld leak detection, personal and fixed safety alarms | Low-cost fixed monitors and controllers |
| Calibration needs | Periodic check against a reference | Regular bump tests and sensor replacement | Regular calibration; sensor head replacement |
| Size | Benchtop / portable (2.1 kg) | Pocket to wall-mount | Pocket to wall-mount |
Decision checklist
- Do you need a defensible number? For lab data, process validation, audits or checking other instruments, choose UV photometry.
- What concentration will you see? Occupied spaces are usually below 0.2 ppm; treatment chambers can run to tens of ppm. The UV-100's three ranges cover both, from 0.01 to 999 ppm.
- Are other oxidising gases present? Chlorine (in water treatment) or nitrogen dioxide (near combustion) can give false readings on electrochemical sensors. UV avoids this.
- Do you need control or a record? Choose an instrument with 4–20 mA output for PLC or generator control, and a data logger for audit trails. The UV-100 has both.
- Do you need a permanent alarm in every room? Fixed electrochemical or HMOS monitors are more economical for multi-point alarms. Use a UV analyser to check them. See our ozone monitors and controllers.
Ozone exposure limits in South Africa
South Africa regulates ozone in two places: workplace air, under the Occupational Health and Safety Act, and outdoor ambient air, under the National Environmental Management: Air Quality Act.
← Scroll to see full table →
| Regulation | Condition | Limit |
|---|---|---|
| Regulations for Hazardous Chemical Agents, 2021 (OEL-RL, 8-hour TWA) | Heavy work | 0.1 ppm |
| Moderate work | 0.16 ppm | |
| Light work | 0.2 ppm | |
| Any workload, 2 hours or less | 0.4 ppm | |
| National Ambient Air Quality Standards (GN 1210 of 2009) | 8-hour running average | 120 µg/m³ (61 ppb); 11 exceedances allowed per calendar year |
| Reference method | UV photometric method, SANS 13964 |
The UV-100's sample-area LED lights above 0.1 ppm, the strictest of the workplace limits. Its 4–20 mA output can trigger extract fans or an alarm at a set point you choose.
South African conditions to plan for
Altitude on the Highveld
At Johannesburg and Pretoria altitudes the air is noticeably less dense than at the coast. A UV photometer counts ozone molecules in its cell, so it must correct for pressure to report ppm correctly. The UV-100 does this automatically with internal temperature and pressure sensors. Remember that µg/m³ conversions also shift with local pressure, while ppm (v/v) does not.
Ambient compliance monitoring
The UV-100 uses the same UV photometric principle as the NAAQS reference method and suits indoor, workplace and process measurements. If you are reporting ambient air quality to a licensing authority, confirm what instrument and quality-assurance requirements apply before choosing equipment. Ask Ecotao to talk through your application.
Ozone in air: frequently asked questions
How is ozone in air measured?
The most accurate method is UV photometry. Ozone strongly absorbs ultraviolet light at 254 nm, so an analyser draws air through an optical cell, measures how much 254 nm light is absorbed, and converts that to a concentration using the Beer–Lambert law. South Africa's National Ambient Air Quality Standards name the UV photometric method (SANS 13964) as the reference method for ozone. Lower-cost electrochemical and heated metal-oxide (HMOS) sensors are used for handheld monitors, leak detection and fixed alarms.
What is a safe level of ozone in air in South Africa?
For workplaces, the Regulations for Hazardous Chemical Agents, 2021 set an 8-hour occupational exposure restricted limit for ozone of 0.1 ppm for heavy work, 0.16 ppm for moderate work and 0.2 ppm for light work, and 0.4 ppm for any workload lasting two hours or less. For outdoor ambient air, the National Ambient Air Quality Standards set 120 µg/m³ (61 ppb) as an 8-hour running average, with 11 exceedances allowed per calendar year.
What is the difference between a UV ozone analyser and an electrochemical ozone sensor?
A UV ozone analyser measures the light absorption of ozone itself, so it is accurate, stable and largely free of the cross-sensitivity that affects chemical sensors. It is the right choice for reference measurements, laboratory work and checking other monitors. An electrochemical sensor reacts chemically with oxidising gases, so it is smaller and cheaper but can also respond to gases such as chlorine and nitrogen dioxide, and it drifts as the sensor ages. It suits handheld leak detection and fixed safety alarms.
What range does the UV-100 ozone analyzer measure?
The Eco Sensors UV-100 measures ozone from 0.01 to 999 ppm (v/v) in three selectable ranges: 0–1.00 ppm, 0–10.0 ppm and 0–999 ppm, with 2% accuracy and a 10-second sampling time.
How do I convert ozone ppm to µg/m³?
At 25 °C and 101.3 kPa, 1 ppb of ozone is about 1.96 µg/m³ and 1 ppm is about 1,960 µg/m³ (1.96 mg/m³). This is why South Africa's ambient standard of 120 µg/m³ corresponds to 61 ppb. Because µg/m³ depends on temperature and pressure, readings at altitude, for example on the Highveld, convert slightly differently, while ppm (v/v) is a volume ratio that does not change with pressure.
Does altitude affect ozone readings in Johannesburg and on the Highveld?
Yes, for uncompensated optical instruments. A UV photometer measures the number of ozone molecules in its cell, and at Highveld altitude the air is less dense, so the instrument must correct for pressure and temperature to report ppm accurately. The UV-100 has internal temperature and pressure sensors and corrects its calibration automatically.
How long does the UV-100 need to warm up?
The published operating instructions call for at least 30 minutes of warm-up, with more than one hour preferred for best accuracy, because the UV lamp and optical bench need to stabilise.
Can the UV-100 log data or connect to a PLC?
Yes. It has a built-in data logger that can be downloaded over USB or serial as a time- and date-stamped data stream, plus 0–2.5 VDC and 4–20 mA analogue outputs for chart recorders, PLCs, SCADA systems or ozone generator control loops.
Where can I buy an ozone in air analyser in South Africa?
Ecotao supplies the Eco Sensors UV-100 ozone analyzer from Cape Town, with delivery across South Africa and to Namibia, Botswana, Zimbabwe, Mozambique, Lesotho and Eswatini. Contact sales@ecotao.co.za or +27 21 911 5835, or check stock on the Ecotao store.
Need help choosing an ozone in air instrument?
Tell us where you're measuring, the concentrations you expect and whether you need logging or control outputs. We supply across South Africa, Namibia, Botswana, Zimbabwe, Mozambique, Lesotho and Eswatini.
- Head office+27 21 911 5835
- Zak086 142 8716
- Zaid082 390 3989
- Emailsales@ecotao.co.za
aqua@ecotao.co.za