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On January 3, NO2 levels were high throughout the territory and those recorded at Mong Kok had breached the 24-hour limit.
The records at other monitoring stations also showed exceedances of the 24- hour NO2 AQO at Kwun Tong and Sham Shui Po.
The high NO2 levels were due to low windspeed, which provided a stable atmosphere for pollutants to accumulate. As there were fresher winds from the sea on January 4, pollutant levels therefore substantially decreased.
On January 25, a TSP level of 259 microgrammes per cubic metre was recorded at Mong Kok, almost reaching the 24-hour Objective TSP limit of 260 microgrammes per cubic metre.
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 interms 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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