Figure 1 shows the Air quality Score plotted against pH values and nitrogen content. The pH of the bark at each
area is not uniform. In polluted areas, there are barks with high pH values as well as low pH values. The same can
be observed for the moderately clean and clean areas where the tree bars show both high and low pH values. The
two triangular diagrams in Figure1 show clear differences between Air Quality Scores and the pH values. Nitrogen
content percentage also shows values which are not uniform. Nevertheless, the linear line obtained showed that the
higher the percentage of nitrogen, the higher the Air Quality Score, especially for the case of negative scores
compared to the positive scores. Other factors influence the values such as the species of the trees are different,
leading to differences in the pH values as in Table 3 (Brodo, 1961; Orange, 1994; Wolseley & Pryor, 1999). Other
factors which influence the experimental results may be due to the direction at which the bark was taken (Young,
1938) and the height of the sample taken (Hale, 1967) as well as the distance of the tree from the source of pollution
at UKM which is the road.
Figure 1. Air Quality Score versus pH value and nitrogen content
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