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SPATIAL AND TEMPORAL ANALYSIS OF NON-URBAN OZONE CONCENTRATIONS OVER THE EASTERN UNITED STATES USING ROTATED PRINCIPAL COMPONENT ANALYSIS
Citation:
Eder, B. SPATIAL AND TEMPORAL ANALYSIS OF NON-URBAN OZONE CONCENTRATIONS OVER THE EASTERN UNITED STATES USING ROTATED PRINCIPAL COMPONENT ANALYSIS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/A-92/124 (NTIS PB92192152).
Description:
The spatial and temporal variability of 03 concentrations over the eastern United States during the period of 1985 through 1990 was examined through the use of a multivariate statistical technique called Principal Component Analysis. he original data set, which contained 77 correlated variables (monitors) was reduced to six uncorrelated principal components, while still explaining almost two-thirds (64.02) of the total variance. pplication of Kaiser's Varimax rotation led to the identification of six separate, contiguous subregions which each exhibit statistically unique 03 concentration characteristics. hen compared to the entire domain, the Great Lakes, Northeast, Southwest and Florida Subregions all observed lower mean 03 concentrations. onversely, the South and Mid-Atlantic Subregions recorded higher than domain means. ariability, as defined by the Coefficient of Variation, was highest in the Northeast, Southwest and Florida Subregions, and lowest in the Great Lakes, South and Mid-Atlantic and Subregions. he percentage of observations exceeding concentration thresholds of 80 and 120 ppb, were higher n the Mid-Atlantic and Southwest Subregions, lower in the Great Lakes and Florida Subregion and near the domain average in the Northeast and South Subregions. A strong seasonal cycle was observed in the Great Lakes, Northeast, Mid-Atlantic and South Subregions. he timing, strength and symmetry varied across these subregions. he Southwest Subregion exhibited little seasonality, while the Florida Subregion contained a strong, out-of-phase seasonality with the maximum occurring during the months of April and May. nnually, the highest 03 concentrations generally occurred during 1988; however, several subregions (Florida and the Southwest) recorded equally high concentrations in other years. o one other year stood out statistically across all subregions. rend analyses indicated a slight, though not statistically significant, decrease in 03 statistics for the Northeast, Mid-Atlantic and Southwest Subregions and a slight increase over the South Subregion. zone concentration trends for the Great Lakes and Florida Subregions were mixed indicating slight increases in mean and median concentrations and slight decreases in the higher percentiles. hese results have provided a statistically and physically based rationale for choosing distinctive geographical areas for interpreting 03 air quality distributions and trends. ince data from stations within subregions exhibit homogeneous variability, we have been able to develop region-wide 03 indicators which have provided meaningful insight into the seasonal and annual concentration trends of the six subregions. he analysis has also suggested that trends analyses for determining general progress in improving 03 air quality could be based on aggregate statistics from clusters of monitors rather than from individual stations.