The influence of synoptic scale meteorology on transport of urban air to remote locations in the SouthWestern United States Of America

Linking air quality at remote sites with synoptic scale atmospheric circulation can provide information regarding the sources of pollutant and may be used to assess the frequency of (and trends in) conditions conducive to long range transport. A methodology for combining tracer studies and regional scale synoptic climatologies is devised herein. Using principal components analysis (PCA) of the 700 and 800 mb heights and precipitable water at 11 radiosonde sites and sea-level reduced surface pressure at 13 surface sites, the dominant modes of atmospheric circulation over the southwestern United States of America are identified and indices of the synoptic scale circulation calculated. These indices are then used as predictor parameters in regression equations of the average daily methylchloroform concentration (a tracer of urban emissions) at two remote sites located to the west of the Grand Canyon National Park, to test the] dependence of ambient methylchloroform concentrations upon prevailing synoptic scale meteorology. It is shown that the influence of synoptic scale conditions is seasonal; the relationship between the average daily methylchloroform concentration at the remote sites and synoptic scale conditions is stronger during the winter season (December-February) than during the summer (June-September).