Sulfur Dioxide: An Outdoor and Indoor Air Pollutant

What sulfur dioxide is
Sources of sulfur dioxide
Health problems caused by sulfur dioxide
   Acute effects to low levels
   Acute effects to high levels
   Repeated, long-term exposure
Decreasing exposure to sulfur dioxide

What Sulfur Dioxide Is

Sulfur dioxide (S0₂) is a colorless gas or liquid with a suffocating and pungent odor. It is a common combustion pollutant. It is an important outdoor air pollutant given off by coal burning power plants. This is because some coal is contaminated with sulfur. When the coal is burned, the sulfur dioxide is released into the air. If there is moisture in the air, the sulfur dioxide dissolves into the moisture creating acid rain (sulfuric acid).

Sulfur dioxide is used in preserving foods, bleaching materials, and as a fumigant. It is generated in metal smelting, burning of fuels, and during the manufacture of paper pulp. In the indoor environment, it is primarily a gas given off because of inadequately vented gas ranges, gas pilot lights, gas or kerosene heaters, and welding activities, as well as tobacco smoke. Because sulfur dioxide is a powerful respiratory irritant, it may aggravate asthma and other respiratory diseases.

Sources of Sulfur Dioxide

The following are some examples of where sulfur dioxide may be found: 

• Unvented or malfunctioning gas appliances such as gas stoves and gas clothes dryers

• Unvented or malfunctioning gas and oil furnaces

• Unvented kerosene heaters

• Wood or coal stoves

• Environmental tobacco smoke

• Automobile exhaust, usually in attached garages

• Malfunctioning chimneys used for wood, gas, or oil exhaust

Health Problems Caused By Sulfur Dioxide

There are many factors that determine if one might get sick due to exposure to sulfur dioxide, including:

• The concentration and amount of sulfur dioxide. Concentrations above 6 ppm produce irritation of the eyes, nose, and throat. Although people with an average sense of smell may begin smelling sulfur dioxide at 2.7 ppm (the odor threshold), the National Istitute of Occupational Safety and Health (NIOSH) recommends that airborne exposure be limited to 2 ppm averaged over 10 hours in the workplace with a level of 5 ppm not to be exceeded for longer than 15 minutes.

• Personal characteristics such as age, gender, weight, general health status. People with asthma are particularly susceptible to the effects of sulfur dioxide. They may have symptoms at levels that are much lower than the rest of the population. Clinical studies have found that some asthmatics respond with bronchoconstriction (narrowing of the airways) to even brief exposure to sulfur dioxide levels as low as 0.4 ppm.

Health problems caused by sulfur dioxide can either be acute, which occur immediately or within a few days of exposure, or they can be chronic, which are long-term health effects that might not show up for many years.

Acute effects to low levels of sulfur dioxide include irritation of the eyes, nose, and respiratory tract. Because sulfur dioxide dissolves easily in water, even low levels can be very irritating. Repeated exposures may result in:¹

• Headache

• Dizziness

• Nausea

Acute effects to high levels can possibly burn the skin and eyes and may result in permanent eye damage. High levels may also cause pulmonary edema (when the lungs fill up with fluid). This is a true medical emergency since oxygen cannot get through the fluid so the person may die.  Sulfur dioxide can also cause the airway passages in the lung to narrow resulting in wheezing, chest tightness, or breathing problems.

Repeated, long-term exposure to lower levels of sulfur dioxide may:

• Decrease pulmonary function

• Cause bronchitis to develop with cough and phlegm production

Decreasing Exposure to Sulfur Dioxide

• Use pilotless (electronic) ignition on gas appliances. These appliances are usually more energy efficient and eliminate the continuous low-level pollutants from pilot lights.

• Install and use an exhaust fan vented to outdoors over gas stoves. Remove and clean the metal mesh filters on your range hoods with detergent when they begin to look grimy (most can be put in the dishwasher). "Ductless" range hoods are not effective because they exhaust into the house rather than outside; add a duct or replace the hood with one vented to the outside (ducted).

• Choose vented appliances whenever possible.

• Before considering using an unvented space heater, check with your local and state building codes and fire ordinances. These types of unvented heaters are not allowed to be used in some communities, dwellings, or certain rooms in the house.

• Choose appliances, such as gas dryers, that vent their fumes to the outside. Have them properly installed and maintain according to the manufacturer's instructions.

• Never disconnect vents on combustion appliances, even if it seems like a way to get extra heat in the winter.

• Never use a gas range for home heating.

• Keep tobacco smoke out of your home and away from open doors or windows. Environmental  tobacco smoke can increase the chance of lung cancer in nonsmokers. Children, pregnant women, or persons with lung or heart disease are especially sensitive to smoke.

• Never idle the car in a garage even if the garage door to the outside is open. Exhaust vapors can build up very quickly in the garage and living area of your home.

• Have a trained professional inspect your fuel-burning appliances, including oil and gas furnaces, gas water heaters, gas ranges and ovens, gas dryers, gas or kerosene space heaters, fireplaces, and wood stoves at the beginning of every heating season. The central heating system (furnaces, flues, and chimneys) should also be inspected, cleaned, and tuned-up annually.

• Install combustion appliances away from the home's living area, such as living room and bedrooms.

• Supply adequate outdoor make-up air for combustion so there will not be backdrafting into the indoor environment.

• Inspect and clean flues and chimneys regularly to make sure they are in good condition and not blocked.

• Use proper fuel in kerosene space heaters. Only use water-clear ASTM 1-K kerosene for kerosene heaters, otherwise you could have even more pollutants get in your home. Never use gasoline in a kerosene heater because it can cause a fire or an explosion. Using even small amounts of gasoline could cause a fire.

• Open flues when fireplaces are in use.

• If a wood stove is used, make sure they are the right size and that they are certified to meet EPA emission standards. Make certain that doors on all wood stoves fit tightly.

• Use an air cleaner to help in removing particulates from the air.

• If your household has young children or someone with allergies or lung disease, consider using a high-efficiency air cleaner in your forced-air heating system or add a stand-alone unit. Some stand-alone air cleaners (HEPA or electrostatic types) can remove particles in a single room; some also can help remove gases. Small desktop air cleaners generally are not effective.

1. New Jersey Hazardous Substance Fact Sheet. Sulfur dioxide. Date accessed October 2000: www.state.nj.us/health/eoh/rtkweb/1759.pdf.