Both wind-driven dispersion of particulates and distant or local anthropogenic emissions can singly or mutually create fluctuations in visual range. In this study, transmissometer data in Tucson, AZ (1997 ¨C 2001) were used to investigate the effects of anthropogenic emissions and circulation patterns on various time scales.

Hourly and diurnal time-scales were analyzed for an anthropogenic signature. Observations of an environmental forcing were also analyzed on a diurnal scale and on synoptic and seasonal scales.

Correlations of visual range with emission levels or wind patterns are presented. The results show that emissions only sometimes explained hourly and diurnal visual range patterns. Circulation patterns, however, were found to better explain the visual range pattern in Tucson on both diurnal and synoptic scales. In particular, early morning drainage flows or 700 and 850-mb winds from the west or southeast were shown to correlate well with visual range fluctuations. The strength of anthropogenic and environmental forcings were less evident on the seasonal scale, in particular summer (JJAS) and winter (NDJF). This is likely due to significant changes in both emission volume and circulation patterns in Tucson.