Air filters and face masks offer little protection to big city air pollution

As I write, it's a warm, sunny afternoon without a cloud in the sky. This looks like a lovely day. Yet checking the Hedley Environmental Index website, I find that air pollution levels are "very dangerous", and from midnight to 1pm today there may have been four preventable deaths and 11,505 doctor visits attributable to breathing Hong Kong's filthy air.

For the money minded, there's also a counter indicating economic costs, which by the time of writing are more than HK$57 million and rising fast.

But even our filthy air seems almost pristine compared to the astonishingly dense smog afflicting Chinese cities including Beijing, where on January 12 the US embassy recorded 886 microgrammes of small particulates per square metre: that's 35 times higher than the World Health Organisation's short term (daily) air quality guideline, which should not be exceeded on more than three days in a year.

While Hong Kong's former chief executive Donald Tsang seemed little concerned regarding air pollution, describing it as "a question of visibility", his successor CY Leung has acknowledged that air pollution impacts public health. Indeed, research suggests that in Hong Kong, it results in more than 3,000 deaths and seven million doctor visits per year. Each kilometre reduction in visibility is associated with an increase in daily deaths from pollution; by Friday this week, visibility reported by Hong Kong Observatory was under 16 kilometres - well below the maximum of over 50 kilometres.

So, what can you do to protect yourself? One apparently promising countermeasure is using an air purifier. These have surged in popularity on the mainland, with sales through the Gome website recently up by 700 per cent compared with previous years. Even China's leaders are using air purifiers, revealing a far less nonchalant attitude to air pollution than did Donald Tsang.