Sulfur dioxide not only has a bad odor, it can irritate the respiratory
system. Exposure to high concentrations for short periods of time can constrict
the bronchi and increase mucous flow, making breathing difficult. Children, the
elderly, those with chronic lung disease, and asthmatics are especially
susceptible to these effects. Sulfur dioxide can also:
Immediately irritate the lung and throat at concentrations greater than 6
parts per million (ppm) in many people.
Impair the respiratory system's defenses against foreign particles and
bacteria, when exposed to concentrations less than 6 ppm for longer time
Apparently enhance the harmful effects of ozone. (Combinations of the two
gases at concentrations occasionally found in the ambient air appear to
increase airway resistance to breathing.)
Sulfur dioxide tends to have more toxic effects when acidic pollutants,
liquid or solid aerosols, and particulates are also present. (In the 1950s and
1960s, thousands of excess deaths occurred in areas where SO2
concentrations exceeded 1 ppm for a few days and other pollutants were also
high.) Effects are more pronounced among mouth breathers, e.g., people who are
exercising or who have head colds. These effects include:
Health problems, such as episodes of bronchitis requiring hospitalization
associated with lower-level acid concentrations.
Self-reported respiratory conditions, such as chronic cough and difficult
breathing, associated with acid aerosol concentrations. (Asthmatic
individuals are especially susceptible to these effects. The elderly and
those with chronic respiratory conditions may also be affected at lower
concentrations than the general population.)
Increased respiratory tract infections, associated with longer term,
lower-level exposures to SO2 and acid aerosols.
Subjective symptoms, such as headaches and nausea, in the absence of
pathologicalabnormalities, due to long-term exposure.
Effects on Plants
Sulfur dioxide easily injures many plant species and varieties, both native
and cultivated. Some of the most sensitive plants include various commercially
valuable pines, legumes, red and black oaks, white ash, alfalfa and blackberry.
The effects include:
Visible injury to the most sensitive plants at exposures as low as 0.12
ppm for 8 hours.
Visible injury to many other plant types of intermediate sensitivity at
exposures of 0.30 ppm for 8 hours.
Positive benefits from low levels, in a very few species growing on sulfur
Increases in sulfur dioxide concentrations accelerate the corrosion of
metals, probably through the formation of acids. (SO2 is a major
precursor to acidic deposition.) Sulfur oxides may also damage stone and
masonry, paint, various fibers, paper, leather, and electrical components.
Increased SO2 also contributes to impaired visibility. Particulate
sulfate, much of which is derived from sulfur dioxide emissions, is a major
component of the complex total suspended particulate mixture.