The Government said today relevant departments have all along been following up on the suspected irritant odour incident reported in different areas of Tuen Mun on October 28.

It noted that the Fire Services Department received 18 emergency calls regarding a pungent odour in Tuen Mun between 3.33pm and 4.25pm on that day.

Officers from the department investigated along Pui To Road, Ming Kum Road, Tin King Road, Shek Pai Tau Road, Ching Chung Koon Road, Tsun Wen Road and its vicinity, and entered the Tai Hing Operational Base. No unusual smell was detected.

On the following two days, the department continued to conduct investigations into the relevant areas and again could not detect any unusual smell. It did not receive any further emergency calls from the public reporting unusual odours in these areas.

Reports were also made to Police since 3.34pm on October 28 of an irritant odour in the vicinity of Tuen Mun. Police investigations could not confirm the odour's cause and origin. The incident was classified as an odd smell found case.

Police also clarified that they did not use tear gas or conduct testing of any unknown gas in Tuen Mun that day, as circulated on the Internet.

Meanwhile, the Environmental Protection Department received 10 complaints of an odd smell between 3.50pm and 4.59pm on October 28. Its officers arrived on site at around 5.35pm and conducted investigations in the vicinity of Tai Hing Operational Base, Blossom Garden, Venice Garden, Tuen Mun North West Swimming Pool, Leung King Estate and Tin King Estate. No obvious smell or suspicious odour could be traced.

The department conducted investigations again on October 29 and 30, with the area expanded to cover Kin Sang Estate, Shek Pai Tau Road, Shan King Estate, Tai Hing Estate, Chelsea Heights, Choy Yee Bridge, Ho Tin Stop, Tuen Mun Stop, Tuen Mun Heung Sze Wui Road and Siu Hei Stop.

Drainage manhole covers as well as exhaust outlets of food premises and industrial buildings along the way in the area were also inspected to trace any possible residue smell or its source, but none was detected.

It analysed the meteorology and air quality monitoring data obtained on October 28, revealing that the South China region was affected by a southward moving northeast monsoon on that day.

The wind direction in Hong Kong changed from easterly to north-westerly since noon and brought in an air mass with a higher background pollution level, resulting in higher than normal pollutant concentrations.

The department said elevated pollution levels in Hong Kong caused by a northeast monsoon occur often in autumn and winter. Its impact could affect various regions in Hong Kong, not only Tuen Mun.

However, the ozone level on October 28 was not exceptionally high for this season. The highest concentration recorded on that day was less than half of the highest value recorded this September. It is not conclusive that ozone was the main cause of the complaints raised.

The Government said relevant departments will continue to monitor the situation and will conduct follow-up investigations if there is new information or irritant odours occur again.