Day of Week Effects on Diurnal Ozone/Nox Cycles and Transportation Emissions in Southern California
/Abstract
Diurnal cycles of ground-level ozone and its precursor NOx concentrations stem from and reflect complex patterning of many underlying factors that follow many different time functions. Investigating and understanding the complexity of ozone and NOx processes are thus crucial to an array of environmental issues such as conducting ozone exposure studies and identifying efficient ozone control measures. Targeting the complete daily ozone/NOx processes, we conducted functional data analysis using continuous hourly ozone and NOx measurements data from the four-month Southern California Ozone Study in summer 1997. In particular, functional analysis of variance (FANOVA) on daily ozone curves from urban and urban peripheral sites, respectively, confirms that the ozone weekend effect (i.e., elevated or comparable ozone concentrations in spite of significantly reduced precursor concentrations on weekends). Although this finding is not new, the capability of FDA to analyze derivatives of functions allows us to examine day-of-week effects on ozone formation/destruction rates. Comparisons of Sunday ozone formation/destruction rates to those on other days demonstrate faster Sunday ozone accumulation rates, which are interpreted from the transportation emissions perspective using Weigh-In-Motion (WIM) traffic monitoring data.
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