Information about Sulfur Dioxide (SO2)
Condensed from Measuring Air Quality: The Pollutant Standards Index;
Office of Air Quality Planning and Standards, US EPA; EPA 451/K-94-001;
February 1994.
Sources
Sulfur dioxide (SO2) is a colorless reactive gas that is
ordorless at low concentrations, but pungent at very high
concentrations. It is emitted primarily when fossil fuels and ores that
contain sulfur are burned or processed. Major sources of SO2 are
fossil fuel-burning power plants and industrial boilers.
Health effects
Exposure to SO2 can cause impairment of respiratory
function, aggravation of existing respiratory disease (especially
bronchitis), and a decrease in the ability of the lungs to clear foreign
particles. It can also lead to increased mortality, especially if elevated
levels of particulate matter (PM) are also present. Groups that appear
most sensitive to the effects of SO2 include asthmatics and other
individuals with hyperactive airways, and individuals with chronic
obstructive lung or cardiovascular disease. Elderly people and
children are also likely to be sensitive to SO2.
Effects of short-term peak exposures have been evaluated in
controlled human exposure studies. These studies show that SO2
generally increases airway resistance in the lungs, and can cause
significant constriction of air passages in sensitive asthmatics. These
impacts have been observed in subjects engaged in moderate to heavy
exercise while exposed to relatively high peak concentrations. These
changes in lung function are accompanied by perceptible symptoms
such as wheezing, shortness of breath, and coughing in these sensitive
groups.
The presence of PM appears to aggravate the impact of SO2 pollution.
Several studies of chronic effects have found that people living in
areas with high PM and SO2 levels have a higher incidence of
respiratory illnesses and symptoms than people living in areas without
such a synergistic combination of pollutants.
Air quality levels
The air quality standard for SO2, which is
designed to protect public health with an adequate margin of safety,
is 0.14 ppm, averaged over 24 hours. EPA is required to issue a
public alert when SO2 levels reach 0.30 ppm on a 24 hour average, a
public warning when SO2 levels reach 0.60 ppm on a 24 hour average,
and a declaration of public emergency at the level of 0.80 ppm. The
significant harm level, at which serious and widespread health effects
occur to the general population, is 1.0 ppm of SO2.
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