CO — Carbon Monoxide Air Quality
Carbon monoxide (CO) is a colorless, odorless gas produced by incomplete combustion of fossil fuels. It is dangerously toxic at high concentrations, reducing the blood's ability to carry oxygen. Both outdoor air quality and indoor CO exposure matter.
Important: Indoor CO Alarm
CO poisoning is a medical emergency. If a CO alarm sounds indoors: evacuate immediately, call emergency services, and do not re-enter until cleared. Symptoms of CO poisoning include headache, dizziness, nausea, and confusion.
What is Carbon Monoxide?
CO forms when carbon-containing fuels (petrol, diesel, gas, coal, wood) burn with insufficient oxygen. When inhaled, CO binds to haemoglobin — 250× more strongly than oxygen — forming carboxyhemoglobin (COHb), which prevents oxygen delivery to organs.
Outdoor CO AQI is measured as an 8-hour average in parts per million (ppm). While outdoor CO rarely reaches dangerous levels in normal conditions, traffic-heavy streets, tunnels, and wildfires can create acute exposure risks. Indoor CO is the greater threat in most cases.
Sources of CO Pollution
- Vehicle exhaust — petrol/diesel vehicles, especially in traffic jams and tunnels
- Gas appliances — faulty or unvented gas boilers, heaters, stoves
- Wildfires and biomass burning — major outdoor CO source
- Industrial processes — steel manufacturing, chemical plants
- Coal combustion — power plants and household coal burning
- Portable generators — extremely high CO risk indoors or semi-enclosed spaces
- Tobacco smoke — indoor CO exposure from smoking
Health Effects of CO
Low-level chronic exposure
- Fatigue and headaches
- Impaired mental function
- Worsened cardiovascular disease
- Chest pain on exertion (heart patients)
High-level acute exposure
- Severe headache, dizziness, confusion
- Nausea and vomiting
- Loss of consciousness
- Brain damage and death (at very high levels)
CO AQI Breakpoints (US EPA)
Based on 8-hour average concentration in parts per million (ppm).
CO Standards
| Standard | Limit | Period |
|---|---|---|
| WHO (2021) | 4 mg/m³ (≈3.5 ppm) | 24-hour |
| WHO (2021) | 10 mg/m³ (≈8.7 ppm) | 8-hour |
| US EPA NAAQS | 9 ppm | 8-hour (not exceed >1×/yr) |
| US EPA NAAQS | 35 ppm | 1-hour |
| OSHA (workplace) | 50 ppm | 8-hour PEL |
| CO alarm trigger | 70 ppm | Sustained (residential) |
Protection Tips
- Install a CO alarm on every level of your home (especially near sleeping areas)
- Have gas appliances (boilers, heaters, stoves) serviced annually
- Never run petrol-powered generators or barbecues indoors or in garages
- Never leave a vehicle running in an attached garage
- During wildfire events, monitor outdoor CO alongside PM2.5 AQI
- Ensure adequate ventilation in parking garages and underground spaces