,many researchers have reported associations for gaseous pollutants
such as nitrogen dioxide. Recent multi-city analyzes conducted in Europe provide further evidence supporting the short-term association of SO2 with adverse health endpoints including both mortality and
morbidity. SO2 is a respiratory irritant and bronchoconstrictor, and has been associated with cardiovascular abnormalities including decrease in heart rate
variability, providing a mechanism by
which SO2 affects cardiorespiratory health.