Day of week effects on diurnal ozone/NOx cycles and transportation emissions in Southern California

Diurnal cycles of ground-level ozone and its precursor NOx concentrations stem from and reflect complex temporal patterning of many underlying factors, including transportation emissions. Investigating the complexity of diurnal ozone/NOx cycles at a finer temporal resolution allows a better understanding of ozone dynamics and helps in designing ozone control strategies. This study applied functional data analysis techniques to hourly resolved ozone and NOx measurement data from the 1997 Southern California Ozone Study. Functional analysis of variance on diurnal ozone/NOx cycles for urban and rural monitoring sites confirmed, in a new continuous functional form, the ozone weekend effect. Functional data analysis also allows for a direct examination of day-of-week effects on ozone formation/destruction rates. Comparisons of Sunday ozone rates to those on weekdays demonstrate earlier, faster, and longer duration of ozone accumulation on Sunday. The results are further interpreted from the transportation emissions perspective using hourly resolved weigh-in-motion traffic data. (c) 2007 Elsevier Ltd. All rights reserved.