Weekly periodicity of environmental variables in Phoenix, Arizona

Though there is no known meteorological cause for weekly cycling of environmental variables, weekly cycles have been discovered at local to global scales, particularly in areas affected by human urbanization. To uncover such cycles in Phoenix, AZ, and to highlight possible mechanisms for their existence, data from several public domain sources were collected and analyzed for cycles in three categories of variables: meteorological, pollution, and human activity measured as vehicle traffic flows. Results indicated that many meteorological and pollution variables do exhibit weekly periodicity and that these cycles are likely due to the weekly pattern of human traffic flows. Atmospheric concentrations of O-3 and NOX gases exhibit a high degree of negative correlation, supporting recent research that suggests anthropogenic NOX gases are effective scavengers of ozone in urban cores. Results further suggest that vehicle-generated NOX gases may be a significant generator of atmospheric nitrate particulates. Finally, both traffic flow and NOX gas concentrations display a strong correlation with wind speed in the urban core, though this study does not speculate on a mechanism for this relationship. (c) 2005 Elsevier Ltd. All rights reserved.