Box and whisker plots of minor element concentrations (ppm) categorized
by traffic density. The x represents mean value, whereas the horizontal line is
median value. All points outside of the box (IQR) and whiskers (min. and max.
values – excluding outliers) are outliers (1.5x below the 1st
quartile or 1.5x above the 3rd quartile). The graph truncates at
3,500 ppm for clarity, omitting a Pb outlier of 6,147 ppm and Sn outlier of
9,339 ppm