🌿 SO₂ in air (UV fluorescence)
Continuous automatic measurement of sulfur dioxide (SO₂) concentration in ambient air by ultraviolet fluorescence method. Reference air quality monitoring method.
Overview
Sulfur dioxide (SO₂) is a gaseous air pollutant formed mainly from combustion of sulfur-containing fossil fuels (coal, fuel oil). SO₂ is toxic to the respiratory system, causes acid rain and smog.
Standard PN-EN 14212 defines the reference method for continuous SO₂ measurement in ambient air, based on UV fluorescence. The method is used in the National Environmental Monitoring (PMŚ) network managed by GIOŚ/WIOŚ. Permissible SO₂ concentrations: 350 µg/m³ (1h), 125 µg/m³ (24h) according to Directive 2008/50/EC and Polish regulation.
Method principle
The air sample is drawn into the analyzer measurement chamber, where it is irradiated with UV radiation at ~214 nm wavelength. SO₂ molecules absorb UV radiation and transition to an excited state, from which they return to the ground state emitting fluorescence at longer wavelength (~330 nm). Fluorescence intensity is proportional to SO₂ concentration and measured by photomultiplier. Interferences (e.g., H₂O, aromatic hydrocarbons) are eliminated by selective optical filter and Teflon membrane.
Applications
- National Environmental Monitoring (GIOŚ/WIOŚ stations)
- Emission monitoring from coal power and heating plants
- Urban air quality assessment
- Monitoring protection zones around industrial plants
- Early warning systems for air pollution
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | 0–500 µg/m³ (typical), expandable to 2000 µg/m³ |
| Detection limit | 0.5–2 µg/m³ |
| Response time (T90) | <120 s |
| 1h limit | 350 µg/m³ (not to exceed >24 times/year) |
| 24h limit | 125 µg/m³ (not to exceed >3 times/year) |
Standard
- Standard number
- PN-EN 14212:2013
- Title (PL)
- Powietrze atmosferyczne — Standardowa metoda pomiaru stężenia dwutlenku siarki metodą fluorescencji w ultrafiolecie
- Title (EN)
- Ambient air — Standard method for the measurement of the concentration of sulphur dioxide by ultraviolet fluorescence
Step-by-step procedure
1. Analyzer installation
Place analyzer in monitoring station with air conditioning (20±5°C). Connect inlet probe and Teflon line.
2. Startup and stabilization
Turn on analyzer. Heat UV lamp (30–60 min). Check sample flow (0.5–1 L/min).
3. Zero calibration
Supply zero air. Set analyzer zero point. Deviation <2 µg/m³.
4. Span calibration
Supply SO₂ calibration gas of known concentration (e.g., 200 µg/m³). Set span point. Deviation <5%.
5. Continuous measurement
Start automatic data recording (1-minute and hourly averages). Data transmission to GIOŚ database.
6. Quality control
Zero and span calibration every 2 weeks. Service every 6 months. UV lamp replacement every 12–18 months.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| SO₂ analyzer (UV fluorescence) | Thermo 43i, Horiba APSA-370, Teledyne T100 | 30,000–60,000 PLN |
| Gas calibrator (permeation or cylinders) | Thermo 146i, Environics 6100 | 25,000–60,000 PLN |
| Zero air generator (synthetic air) | Thermo 111, carbon filter + dryer + HEPA filter | 10,000–25,000 PLN |
| Sample intake system with probe | PM₁₀ probe with filter and Teflon connection | 2,000–5,000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Calibration gas SO₂ | 7446-09-5 | Cylinder SO₂/N₂, 50–500 ppb, certified ±2% |
| Zero air | — | Synthetic air free of SO₂ (<0.5 ppb), from generator or cylinder |
Health and safety (OHS)
- SO₂ — toxic gas, respiratory irritant. Store cylinders in ventilated area.
- Pressure cylinders — use regulators and safety devices
- Monitoring station — ensure ventilation and gas detector