XN000022-1996-06-14 — Page 22

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The reported air pollutants include sulphur dioxide (SO2), nitrogen dioxide (NO2), total suspended particulates (TSP) which comprise all sizes of dust particles, and the respirable fraction of the dust (RSP). All these

All these pollutants can affect respiratory health in sufficient concentration. .

On May 10, RSP concentrations were high throughout the territory, with exceedances of the 24-hour Air Quality Objective (AQO). The situation was believed to be associated with the strong easterly winds, which blew up the settled dust in Hong Kong and in the region.

For SO2 and NO2, there was no exceedance of the 24-hour AQOs at the three stations.

The gases and particles described originated from various sources. SO2 is mostly produced when fuels that contain sulphur are burned. NO2 is formed during combustion by the combination of nitrogen and oxygen, and by the atmospheric oxidation of nitric oxide (NO), also a product of combustion.

Vehicle exhaust is an important source of NO and NO2 in terms of impact on local air quality. It is also a major source of airborne particulate matter, especially the smaller respirable particles.

Diesel-engined vehicles such as taxis, public light buses, passenger coaches, franchised buses and light and heavy goods vehicles are the greatest contributor of particulate matter. Other sources include industry, furnaces and boilers, construction activities, the sea and the soil.

It is worth noting that while the weather and climate always affect the concentrations of pollutants in the air, the only sure way of reducing the levels is to reduce emissions from the man-made sources.

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