The table below provides guidance on how to respond to different concentrations of sulphur dioxide (SO2) in the air. The different concentration levels are color coded for clarity. Each color represents potential health effects for both healthy individuals and sensitive groups (e.g. children and people with pre-existing health conditions*), along with the most appropriate response for each. The colors match those used for other air quality pollutants on airquality.is but the responses and recommendations in the table only apply to SO2 pollution.
The recommendations are based on a maximum exposure time of 10-15 minutes. Longer exposure may result in more severe health effects. These guidelines aim to ensure that daily activities can continue as usual while reducing the adverse effects of SO2 exposure.
Short term effects of SO2 exposure. Effect descriptions are based on 10-15 min. exposure.
| SO2 for 10─15 min. | Air quality levels and effect on people | Recommended response | ||
|---|---|---|---|---|
| µg/m3 | ppm | Children, individuals with pre-existing health conditions and sensitive individuals* | Healthy individuals | |
| Very good | ||||
| 0 - 20 | 0 - 0.1 | Usually no adverse health effects. | Adverse health effects unlikely. Young children can sleep outside in a stroller. | Adverse health effects unlikely. |
| Good | ||||
| 21 - 350 | 0 - 0.1 | Usually no adverse health effects. | Adverse health effects possible. Young children should not sleep outside in a stroller. | Adverse health effects unlikely. |
| Medium | ||||
| 351 - 600 | 0.1 - 0.2 | Sensitive individuals: Can cause irritation (coughing) in airways of sensitive individuals. Healthy individuals: Irritation in eyes, nose and throat. | Proceed with caution, monitor measurements. Limit outdoor exertion if symptoms arise. Young children should not sleep outside in a stroller. Older children should limit outdoor exertion. Turn air conditioning off. | Adverse health effects unlikely. Turn air conditioning off. |
| Bad | ||||
| 601 - 2,600 | 0.2 - 1.0 | Sensitive individuals: Coughing, irritation in eyes, throat and nose. Healthy individuals: Can cause symptoms in airways and irritation in eyes, nose and throat. | Avoid outdoor exertion and children should not be outside except while going to/from school. Turn air conditioning off. | Adverse health effects unlikely but try to limit outdoor exertion and breathe only through nose. Turn air conditioning off. |
| Very bad | ||||
| 2,601 - 9,000 | 1.0 - 3.0 | Sensitive individuals: Coughing and headaches. Irritation in eyes, nose and throat. Healthy individuals: Same symptoms but milder or minimal. | Stay inside and close windows. Turn air conditioning off. | Avoid outdoor exertion. Try to stay indoors. Try to breathe only through your nose. Close windows and turn air conditioning off. |
| 2,600 | 1.0 | Occupational safety limit for 15 minutes. | Any outside work prohibited unless with an adequate gas mask and gas monitor. | Any outside work prohibited unless with an adequate gas mask and gas monitor. |
| Severe | ||||
| 9,000 - 14,000 | 3.0 - 5.0 | Everyone likely to feel moderate to severe respiratory system symptoms. | Stay inside and close windows. Turn air conditioning off. Follow instructions from local authorities. | Stay inside and close windows. Turn air conditioning off. Follow instructions from local authorities. |
| Emergency | ||||
| > 14,000 | > 5.0 | Severe respiratory system symptoms are likely for both healthy and sensitive individuals. | Stay inside and close windows. Turn air conditioning off. Follow instructions from local authorities. | Stay inside and close windows. Turn air conditioning off. Follow instructions from local authorities. |
Summary of SO2 health effects
Most of the SO2 that enters the upper respiratory tract is absorbed through the mucous membrane. There it is metabolized in the liver and excreted by urine. Very little accumulates in the body, and damage to internal organs has not been reported. Additionally, bacteria in the nose and throat produce various substances that bind SO2 and render it inactive.
If SO2 pollution exceeds health limits, it’s important to breathe calmly through the nose and avoid exertion. Young children should not sleep outside in a stroller when SO2 pollution is persistent or during pollution peaks and everyone should avoid strenuous outdoor activities. Sensitive groups should consult healthcare professionals for further advice.
The health effects of air pollution depend on the duration of exposure. If exposure lasts longer than 10–15 minutes, greater health effects can be expected than indicated in the reference chart.
Long-term effects of SO2 exposure
Research suggests that long-term exposure to SO2 polluted air can cause persistent respiratory symptoms, such as coughing, nasal discharge, and asthma. Many studies also indicate that pollution can lead to fetal growth restrictions and preterm births. There is no evidence that SO2 pollution causes cancer, and it remains unclear whether it contributes to high blood pressure or infertility.
Steps to reduce indoor SO2 pollution
- Dissolve a teaspoon (5 g) of baking soda in 1 liter of water.
- Soak a rag or dishtowel in the solution.
- Wring most of the solution out of the cloth so it doesn't drip.
- Hang the cloth in the room you intend to depollute.
- Have a fan blow air on the cloth.
- The cloth needs to remain damp for it to retain its depolluting properties. In case it dries out, wet it again with water from a spray bottle or other means.
- If the pollution persists for a long time the cloth needs to be rinsed under cold water twice a day and soaked in the baking soda solution again.
Unavoidable outdoor activities during heavy pollution (> 2600 µg/m3)
If people must move between places whilst heavy pollution persists, causing discomfort, it’s useful to cover the nose and mouth with a damp cloth or dust mask since the moisture absorbs SO2 particles. Soaking the cloth or mask in a solution of baking soda, like described above, will enhance the effect. Note that there’s more resistance in a wet cloth or mask which makes breathing harder. This trick only works for a short period of time (10-15 minutes) and is not adequate for working for longer periods during periods of heavy pollution. Should SO2 levels exceed 2600 µg/m3, all outdoor work should be stopped unless absolutely necessary (e.g. scientific measurements close to volcanic activity) in which case recommendations of The Administration of Occupational Safety and Health should always be followed.
Occupational safety limits
Should SO2 concentration in air exceed 1300 µg/m3 over an 8 hour average, working hours should be reduced in proportion to pollution levels unless workers use adequate gas masks and personal SO2 monitors. Should the concentration exceed µg/m3 over a 15 minute period all work should cease unless workers use adequate gas masks and personal SO2 monitors.