Scientists' Contributions

Mapping of Particulate Air-Pollution on Beijing by Plant Bio-Monitors

J. P. Garrec^*, Shang He^**, C. Rose^*, F. Radnai^*

    Beijing is known for its high level of air pollution, but the town is only equiped by a small air monitoring network and for this reason nothing is known about the location of the different polluted areas, their surface and their level of pollution.

    In relation to the franco-chinese cooperative programme of advanced research (PRA), the first air pollution maps of Beijing have been drawn up.

    In a first step, Beijing has been divided into 211 square mails.

    During summer 1998, leaves have been sampled on one poplar in each mail. Poplar (Populus tomentosa) is the tree which is the more frequent on Beijing, and the tree selected in each mail was a tree representative of the local mean AIR pollution level. Particles have been extracted with the cuticular waxes from the surface of the polluted leaves by chloroform, and then collected on a filter. Particles (shape, size, quantity, mineral composition) have been then studied and analysed by an X ray microanalyser.

    Among the different elements analysed in the particles, 2 elements Fe and S, are particularly interesting.

• Fe is an element characteristic or a tracer of the air pollution linked to road or railway traffic,
• S is an element characteristic or a tracer of the air pollution linked to domestic or industrial use of energy from coal or fuel.

    From the identification of 3 classes of iron and sulphur pollution and mapping air pollution on the town of Beijing, it is now possible to determine the position and the surface of the different polluted areas with their levels, and also to identify the main sources of pollution and their impacts.

    At the level of the sulphur pollution, the results and the air pollution map show that this pollution is mainly present downtown, area of old habitat where coal is still largely used as an energy source, but also on some places, just at the periphery of the town of Beijing.

    At the level of the iron pollution, the results and the air pollution map show that now on Beijing, as on all the megacities of the world, the air pollution coming from the road traffic is widespread. This pollution is detected everywhere on the town of Beijing, but particularly near and between the 2 main circle boulevards of the town.

Conclusion

    The different air pollution maps show for the first time the trend of air pollution localization and level on Beijing, and at the same time confirm the validity of this new method using plant bio-indicators to study air pollution.