Last month Better Air Quality (BAQ) in Asia biennial conference was held in Bangkok. It highlighted one of the most pressing issues for the mega cities of Asia - the need to improve air quality while urbanization increases apace and along with it energy consumption and vehicle growth.

Air quality in Asia is certainly improving but is still far above World Health Organization limits. Particular matter (dust) is the main pollutant of concern while ozone is increasingly becoming a problem.

Let us be clear from the outset about the health, environmental and economic impacts of air pollution. On the health front, it has been shown in studies across the globe to have significant effects on the lungs, the heart and the nervous system.

The environmental impact in Asia also includes damage done to agriculture by air pollution originating from cities, including sulphur dioxide, ozone and acid rain. Estimates of the consequent losses to the economy vary from 1 to 3 percent of GDP.

While the BAQ conference was taking place, one particular Asian capital faced some very severe air pollution problems - Delhi with its winter "fog", which came early this year.

One of the first things that strikes visitors to India is the low-lying soup that hangs over its capital city, as the early morning moisture mingles with fumes and dust to form a cloud that lasts all day. As a result, Delhi has been ranked as one of the worst polluted cities by the World Bank.

This fog often delays flights at the Indira Gandhi International Airport because of the poor visibility, which at the peak of winter falls to just 50 m. Hospitals are also recording an increase in patients with respiratory problems, with doctors prescribing oxygen nebulizers for young children suffering "bad air" asthma attacks. We even find professional Delhites leaving the city to spare their children from pollution-related illnesses.

India's fast-expanding economy and growing prosperity has led to an increase in the number of cars that clog Delhi's roads. Delhi is now estimated to have 5.5 million cars, an increase of over 57 percent in eight years.

This steep rise in car use has rolled back the gains achieved by introducing compressed natural gas (CNG) vehicles, particularly among buses and motorized rickshaws. The problem also faces cities like Kolkata and Dhaka, where similar gains from CNG have been made, only to be negated by the huge growth in car ownership.

The Central Pollution Control Board of Delhi has suggested two explanations for what it calls "the smoke phenomenon". While it maintains that levels of sulphur dioxide and carbon monoxide have fallen considerably over the past eight years (though the latter is still above the prescribed level), it argues that adverse meteorological conditions mean pollution is not dispersed and collects at lower levels.

Second, it suggests that a rise in particular matter has been registered, put down largely to construction work for the Commonwealth Games and Delhi Metro.

We in London have faced similar problems. It is over half a century since the Clean Air Act of 1956 cleared London skies of smog. Faced with major air pollution - and in particular, the great smog of 1952, which killed some 4,000 people in London - the government of the day applied mandatory smokeless zones to British cities. Within just three years the use of coal disappeared from our larger cities and Londoners breathed more easily. So effective legislation can make a big difference.

Asian cities have two central challenges to be considered. Firstly how can cities realize their economic and social development goals while at the same time minimizing the use of fossil fuels, directly associated with air pollution? And if fossil fuels are used in the future, how can their combustion be carried out in the most clean and efficient manner? Moreover, we need the right mix of technology and demand management in reducing air pollution.

Advances have been made in technologies like fuel economy, energy efficiency and the use of cleaner (low sulphur) fuels in the last 20 years, which allow for considerable reductions in air pollution levels. But there is a danger that reductions achieved through these cleaner technologies will be offset by the rapid growth in the number of emission sources, as we have already noted is the case in some South Asian cities. Cleaner technologies will need to be combined with non-technological, demand-management approaches of which the most obvious is investment in public transport.

Finally do not forget that air quality is not just a day-to-day concern but also poses a specific challenge at major events - as was illustrated by the most recent mega event, the Beijing Olympic Games.

The Beijing authorities managed to deal with the issue by a combination of measures, including the car licensing scheme with its odd-even license plate restrictions. So successful were they that air quality did not affect the performance of the Olympic athletes at all, as critics had suggested it would.

Delhi could learn some important lessons here for its own hosting of a major sporting event, the Commonwealth Games in 2010. So let us hope for a fruitful exchange between Beijing and Delhi on this front.

(China Daily December 25, 2008)