Hebdomadal and diurnal cycles in ozone time series from the Lower Fraser Valley, B.C.

Abstract

The variability of tropospheric ozone concentrations on diurnal and hebdomadal time scales provides information regarding the processes of ozone formation, destruction and transport. This paper presents the statistics of ozone concentrations at 12 sites in the Lower Fraser Valley, B.C. Canada, with particular emphasis upon these time scales. Using a range of statistical techniques, the presence of hebdomadal cycles in the summertime ozone and oxides of nitrogen (nitrogen dioxide and nitric oxide) time series is demonstrated. Ozone concentrations at all sites are found to vary by day of the week and to be uniformly higher on weekends than mid-week. Conversely, oxides of nitrogen concentrations are typically, but not uniformly, higher mid-week than during weekends. The magnitude of the hebdomadal cycles of ozone and oxides of nitrogen (weekend-mid-week differences in concentration divided by the mean summertime concentration) is spatially variable and apparently has increased over the period 1984–1991. The methodology of Lefohn and Shadwick (1991) is used to show that at five sites in the LFV the form of the summertime average diurnal profiles of ozone and oxides of nitrogen on weekends and mid-week also changed between 1984 and 1991. The spatial and temporal variability of hebdomadal and diurnal ozone cycles are interpreted in the context of precursor emissions variability.