3.2. Factor analysis
The covariance matrix with the 13 analyzed variables was constructed using normalized data and, therefore, coincides with the correlation matrix (Table 3). Several clear atmospheric chemical relationships could be readily inferred including high positive correlation (values in bold, r = 0.267 to 0.918) between 1–OHPYR and 2–OHPH, and between the two compounds and NO, NO2, N2Ox and SO2 levels along with atmospheric pressure, solar radiation, etc. The highest correlation was the one observed between the levels of the two compounds. Positive correlation was detected between the OH–PAHs and the nitrogen and sulfur oxides, while increases in ozone, temperature and radiation were linked to a reduction in hydroxylate concentrations. These findings seem to confirm the conclusions drawn about the formation of hydroxylated compounds in the atmosphere via photochemical reactions. Moreover, the purported relationship between airborne OH–PAH in fine particulate matter and estrogenic activity emphasizes the potential interest of yearly monitoring of these compounds. The Bartlett chi–squared statistic of Bartlett's sphericity test was 1 117.6 (the critical value is 99.6 for 78 degrees of freedom at the 95% significance level, p = 0.000), indicating that the variables examined are not orthogonal but correlated. This means that data variability could be explained with a lower number of variables (or principal components, PC).
3.2. Factor analysis The covariance matrix with the 13 analyzed variables was constructed using normalized data and, therefore, coincides with the correlation matrix (Table 3). Several clear atmospheric chemical relationships could be readily inferred including high positive correlation (values in bold, r = 0.267 to 0.918) between 1–OHPYR and 2–OHPH, and between the two compounds and NO, NO2, N2Ox and SO2 levels along with atmospheric pressure, solar radiation, etc. The highest correlation was the one observed between the levels of the two compounds. Positive correlation was detected between the OH–PAHs and the nitrogen and sulfur oxides, while increases in ozone, temperature and radiation were linked to a reduction in hydroxylate concentrations. These findings seem to confirm the conclusions drawn about the formation of hydroxylated compounds in the atmosphere via photochemical reactions. Moreover, the purported relationship between airborne OH–PAH in fine particulate matter and estrogenic activity emphasizes the potential interest of yearly monitoring of these compounds. The Bartlett chi–squared statistic of Bartlett's sphericity test was 1 117.6 (the critical value is 99.6 for 78 degrees of freedom at the 95% significance level, p = 0.000), indicating that the variables examined are not orthogonal but correlated. This means that data variability could be explained with a lower number of variables (or principal components, PC).
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