Plants were used to monitor and evaluate the atmospheric environment of Guangzhou city in 1981. 18 sites were chosen within the city for monitoring and one site of Nan Hu at the outskirts of Guangzhou was chosen for control. On each site, we sampled four plants species for measuring the sulphur content in their leaves. Sampling were made four times in a year: spring, summer, autumn and winter, inflammation method was adopted.

The sulphur content index was calculated by the following formula:

IPC=Cm/Ck

According to this index, four classes of pollution can be distinguished: Ⅰ.clean (<1.0); Ⅱ. light (1.1–1.5); Ⅲ. medium (1.6–2.0); Ⅳ- heavy (>2.1).

Evalution:

1. Comparing by graphic curves, it comes into notice that there were 69 sites among 70 sulphur content index (99%) with higher sulphur content than that of the control. Among the 4 plant species studied, three were found in Li Wan District with maximum amounts of sulphur.

2. According to classes of pollution 12 (17%) out of the 70 indices belong to heavy. Among 14 indices in Li Wan District, 7 belong to heavy (50%), which means that Li Wall District is one of the serious polluted area by SO2.

3. Comparing by correlation coefficients, we used the annual mean value of the four plant species as independent variables (x), and that of the atmospheric sample as dependent variables (y). The formula:

was used to evaluate the correlation coefficients of these four species. The values obtained were 0.27, 0.49, 0.55 and 0.48 respectively. It shows clearly that the x and y are positively correlated.