By Grace Li
HONG KONG (Reuters) - Hong Kong residents breathed in the worst air of 2013 on Monday, joining citizens in mainland China who have been choking on dangerously high pollution levels, and further undermining the city's role as an Asian financial centre,
Air pollution index readings hit their highest levels this year at roadside monitoring stations in Mong Kok and Central, home to financial institutions such as HSBC Holdings and Standard Chartered, recording "severe" levels of 205 and 210, respectively.
More than half of the 11 stations in areas with less traffic recorded "very high" levels between 103 and 140.
The situation was caused as pollutants, in particular nitrogen dioxide, became trapped within the city where skyscrapers packed together stop air from circulating, a spokesman for the Environmental Protection Department said.
People with heart or respiratory illnesses, the elderly and children were advised to stay indoors as the city's iconic harbor was shrouded in thick smog and the skyscrapers of Hong Kong island were barely visible from Kowloon.
The pollution index in Beijing on Monday stood at 167, or "unhealthy" levels, according to the United States embassy, which most Chinese rely on for more accurate readings.
The Hong Kong index uses different criteria to measure pollution, so has different numerical readings.
Hong Kong is seeing increasingly high pollution index readings this year due to the rising number of vehicles on the city's already congested roads, said Melonie Chau, Friends of the Earth's senior environmental affairs officer.
Air pollution in Hong Kong, a former British colony which returned to Chinese rule in 1997, is a major source of worry for local citizens and foreign businesses, which increasingly see it as compromising the quality of life.
There were 322 premature deaths in Hong Kong in March as a result of adverse health effects due to air pollution, according to Hong Kong University's Hedley Environmental Index.
Surveys have continuously found that the city's pollution is hurting its competitiveness, undermining its role as a financial centre as some executives relocate due to health concerns.
Hong Kong leader Leung Chun-ying has pledged to make improving air quality a priority.
In his maiden policy speech in January, Leung proposed HK$10 billion ($1.29 billion) in subsidies to phase out over 80,000 heavy-polluting diesel vehicles, while fresh emission reduction targets have been set with neighboring Guangdong province - a major source of cross-border pollutants from tens of thousands of factories in the Pearl River Delta.
In Beijing, a city of around 20 million people, air quality has mostly stayed above "very unhealthy" and "hazardous" levels since the beginning of this year.
An official newspaper reported last month that China would spend 100 billion yuan ($16 billion) over three years to deal with Beijing's pollution, as the government tries to defuse mounting public anger over environmental degradation.
(Reporting By Grace Li; Editing by Anne Marie Roantree and Michael Perry)