The current National Ambient Air Quality Standards (NAAQS) for sulfur dioxide were set in 1971. However, peak levels of SO2 in the air can cause temporary breathing difficulty for people with asthma who are active outdoors.
The Integrated Science Assessment (ISA) concludes:
“Collectively, the human clinical, epidemiologic, and animal toxicological data
are sufficient to conclude that there is a causal relationship between
respiratory morbidity and short-term exposure to SO2. Observed associations between SO2 exposure and an array of respiratory outcomes, including respiratory symptoms, lung function, airway inflammation, airway hyperreactivity, and emergency department visits and hospitalizations from the human clinical, animal toxicological, and epidemiologic studies, in combination, provide clear and convincing evidence of consistency, specificity, temporal and biologic gradients, biological plausibility, and coherence.”
“Human clinical studies consistently demonstrate respiratory morbidity among exercising asthmatics following peak exposures (5-10 min) to SO2 concentrations ≥ 0.4 ppm, with respiratory effects occurring at concentrations as low as 0.2 ppm in some asthmatics. In the epidemiologic
studies, the SO2-related respiratory effects were consistently observed in areas where the maximum ambient 24-h avg SO2 concentration was below the current 24-h avg NAAQS level of 0.14 ppm.”
“Potentially susceptible and vulnerable subgroups include asthmatics, children, older adults, and individuals who spend a lot of time outdoors at increased exertion levels.”
A copy of the Integrated Science Assessment is available online.