The study area comprises 27 areas consisting of 110 trees which were selected according to some characteristics
surrounding the campus of Universiti Kebangsaan Malaysia, Bangi, Selangor. The location of of each tree is
recorded using GPS. The method of determination of air quality is to use a counting technique for the frequency of
lichen growth in 10 squares of a quadrant where the frequency is the number of squares on the quadrant which
contain the lichen. The lichens are categorized into three groups based on the tolerance towards air pollution, i.e.
tolerant, moderate and sensitive group. Table 1 shows the division of lichen species according to their tolerance
towards air pollution.