Day-of-week behavior of atmospheric ozone in three US cities

The weekly cycles of atmospheric ozone (O-3) are of interest because they provide information about the response of O-3 to changes in anthropogenic emissions from weekdays to weekends. The weekly behavior of O-3 in Chicago, IL; Philadelphia, PA; and Atlanta, GA, is contrasted. In Chicago and Philadelphia, maximum 1-hr average O-3 increases on weekends. In Atlanta, O-3 builds up from Mondays to Fridays and declines during weekends. In all three areas, volatile organic compound (VOC)/nitrogen oxides (NOx) ratios are higher during weekends, resulting from greater than proportionate decreases in NOx relative to VOC emissions. The VOC/NOx ratios, correlate with maximum 1-hr O-3 concentrations in Chicago, a response consistent with a VOC-sensitive airshed. A weak correlation between O-3 concentrations and VOC/NOx ratios in Philadelphia suggests the impact of transported O-3, which is formed in upwind VOC-sensitive locations that may be hundreds of kilometers away. Ozone concentrations in Atlanta do not correlate with VOC/NOx ratios but with concentrations of NOx and total reactive nitrogen (NOy) carried over from the previous day. When data from 1986-1990 and 1995-1999 are compared, only small differences in. the weekly behavior of O-3 are observed in Chicago and Philadelphia. The day-of-week differences in O-3 are amplified in the more recent period in Atlanta, a possible result of urban growth.