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 pollutants can affect respiratory health in sufficient concentration.
Air quality was poor on August 20. The Mong Kok Station recorded high NO2 levels of 159 ug/m3 which was about six per cent higher than the daily air quality objective (AQO).
The ozone concentration was also very high for a few hours in the territory at late afternoon. The peak concentration of ozone of 314 ug/m3 or about 30% higher than the air quality objective was recorded at the Central/Western Station.
The ozone was formed by reactions between other air pollutant such as nitrogen oxides and hydrocarbons, in the presence of strong sunlight.
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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