Observations of the chemical evolution of the Sacramento, CA urban plume

The Sacramento Valley and the Mountain Counties to its East in California routinely violate the U.S. Federal 8-hour O₃ standard between May and October. We describe observations of NO₂, total peroxynitrates, total alkyl nitrates, HNO₃ and a wide range of VOC and O₃ at three sites along the outflow of the urban plume (2hrs, 6hrs and 7hrs downwind). We present an analysis of the weekend effect in O₃ at several sites in the area for the last five years, showing that sites in the valley generally have higher weekend ozone while sites downwind have lower ozone. The measurements are used to examine our understanding of the chemical and transport processes responsible for the weekend/weekday differences in O₃, biogenic VOC, NO₂, HNO₃, peroxynitrates and alkyl nitrates. Relationships among the hydrocarbons and ratios of oxidized nitrogen to NO₂ will be used to compare and contrast HO_x chemistry and the rate of ozone production on weekdays and weekends.