Ozone concentrations at sites downwind of the New York City metropolitan region decrease on weekends. Concentrations within and upwind of the region are very nearly the same on weekdays and weekends, which agrees with earlier analyses of data in this region. For concentrations above the Federal Standard of 80 ppb, the reduction in Connecticut, which has the highest ozone concentrations in the Northeast, is approximately 20 percent. This weekend reduction carries over into Monday, which has concentrations approximately the same as those on weekends. This is then followed by a gradual increase from Tuesday to Friday. The reductions in ozone concentrations on Saturdays, Sundays, and Mondays correspond to reductions in traffic which occur on these days of the week. The fitting of a time series model with periodic means, variances, and autocorrelations shows the observed reductions are statistically significant.