Seasonal transport of fine particles to the Grand Canyon

Potential sources of pollutants can be identified by analyzing back traject ories associated with extreme ambient concentrations. Conditional frequency analysis (CFA) was used to identify statistically significant associations of geographical regions and ambient air quality observed at sites near the Grand Canyon. Stratification by season reveals a pattern of association du ring the fall quarter that is not observed during other seasons. Applicatio n of CFA to different source tracers provides additional information on the nature of the associations. Tracer species that were often below detection limits can be studied because the method requires only that the highest co ncentrations be identified.