The occurrence of elevated levels of ozone smog is very related to specific weather conditions. In New England, sustained southwest winds are almost always necessary in order for unhealthy levels of smog to occur. Additionally, hot temperatures and sunny skies are necessary to promote the photochemical reactions that contribute to the build up of ozone in the lower atmosphere.

View ozone concentrations and corresponding weather conditions for a day in 1998 when high concentrations of ozone smog were measured across southern New England.