Initial Characterization of Fine Particulate Matter (PM2.5) Collected By the National Federal Reference Monitor Network
Data collected between January to December, 1999 were polled from the USEPA Aerometric Information Retrieval System. For the purpose of this analysis, data which were flagged with qualifiers related to laboratory and monitor malfunctions were removed from the data set. Analyses of the temporal and spatial variability of PM 25 concentrations were performed for selected metropolitan statistical areas (MSAs) and for broader predefined regions of the country. The temporal variability of PM25 concentrations was examined on hourly to seasonal time scales. The spatial variability of PM25 concentrations was examined within several MSAs and on the regional scale. Data obtained during 1999 by the PM25 FRM network were also compared to data obtained in a number of specialized field studies conducted in prior years.
The seasonal variability of PM25 concentrations shows distinct differences in patterns in moving from the East to the West. There is an overall shift in the highest seasonal mean concentrations from the summer to the winter from the East to the West. These differences are related to differences in source characteristics. The results of spatial analyses, conducted on data from several MSAs across the country, show a linear decrease in the correlation coefficient between site as the distance between them increases. For many MSAs, however, correlations between sites remained relatively high (R2>0.7) for distances up to 100 km, supporting the hypothesis that PM25 is essentially a regional pollutant. A number of other characteristics of the data set will also be presented.