Hong Kong air pollution

Cold wet weather to persist but will help disperse pollution: scientists

PUBLISHED : Sunday, 15 December, 2013, 7:09pm
UPDATED : Monday, 27 April, 2015, 3:29pm

Cold, wet and gloomy best describe what the city’s weather will be like this coming week, as temperatures are forecast to drop as low as 10 degrees Celsius in the next few days.

The northeast monsoon over southern China is expected to prolong the cold spell across the region this week and bring along with it lots of rain.

Several areas of the city recorded up to 10 millimetres of rainfall on Sunday, as a rain band continued to envelop Guangdong province, according to the Hong Kong Observatory.

Acting senior scientific officer Li Ping-wah said temperatures will continue dropping on Monday night and by Tuesday morning fall to about 10 to 11 degrees.

“We urge the elderly and those with chronic medical conditions to take precautions to protect themselves against the cold weather,” he added. “Temperatures will not see an uptick until the weekend.”

Rainfall in the past few days has helped bring air pollution levels to more moderate levels following steep spikes in pollutants at three monitoring stations on Saturday.

General air pollution monitoring stations in Yuen Long, Tap Mun and Tung Chung recorded levels of respirable suspended particulates, or RSPs, as high as 80 to 100 – far above average levels of roadside monitoring stations, which are typically higher.

The World Health Organisation considers any air pollution index (API) reading above 25 as “dangerous” and any readings above 75 as “very dangerous”.

Polytechnic University environmental engineering professor Wang Tao said general API could sometimes exceed roadside API recordings in sub-urban areas such as Tung Chung and Tap Mun due to higher levels of secondary photochemical pollutants, such as ozone, which could come from distant sources.

He said it was possible that some of pollution in the last few weeks could have come from the wider Pearl River Delta region.

“In the past, northeast monsoons have brought high level of pollutants from the continental mainland to Hong Kong,” Wang explained, adding that air pollutant levels usually see a sharp increase when warm air meet colder air fronts.

Levels of PM2.5 – tiny particles in the air which are particularly hazardous to health – are typically higher in late autumn and early winter when the weather is dry.

“Rainy weather this week will help disperse much of the pollutants and lower the API,” said Wang.

According to Environmental Protection Department data on Sunday, six districts – Causeway Bay, Kwun Tong, Sham Shui Po, Tai Po, Tung Chung and Yuen Long – recorded levels of PM2.5 higher than the WHO standard of 25 micrograms per cubic metre.