Respiratory Effects from Sulfate Particles – SO₂ reacts with other chemicals in the air to form tiny sulfate particles.  When these are breathed, they gather in the lungs and are associated with increased respiratory symptoms and disease, difficulty in breathing, and premature death.

Short-term Peak Levels
High levels of SO₂emitted over a short period, such as a day, can be particularly problematic for people with asthma.  EPA encourages communities to learn about the types of industries in their communities and to work with local industrial facilities to address pollution control equipment failures or process upsets that could result in peak levels of SO₂.

http://www.epa.gov/oar/urbanair/so2/hlth1.html