Toxic smog shrouds New Delhi New Delhi was on Wednesday enveloped in a cloud of toxic smog thought to be the worst occurrence of air pollution in a city long accustomed to dirty air, with the density of dust particles in some places reaching 30 times the guidelines set by the World Health Organisation. "Definitely it's the worst it's ever been," said Sunita Narayan, director-general of the Centre for Science and Environment (CSE), a New Delhi-based advocacy group. But Delhi's air has been getting worse every year. Visibility outside fell to a few hundred metres, hiding the sun, and the smog was perceptible even inside homes and offices, to the dismay of Indian business leaders and foreign dignitaries attending a meeting of the World Economic Forum on India in Gurgaon, a satellite city near Delhi. My friends have been saying this is fall [autumn]. I said it's not just the fall, it's smog," said Rajat Nag, managing director-general of the Manila-based Asian Development Bank, who comes from Delhi. It's very worrisome . . . Asia's growth story can really come unstuck on the environment issue. Although pollution in the Chinese capital, Beijing, is better publicised, studies have shown that India has the world's worst air pollution and that air quality has deteriorated steadily over the past decade for the 22m inhabitants of the Delhi metropolitan area. For particulate matter of less than 10 micrometres in diameter, one monitoring station in Delhi showed levels of 1,008 at 12.40 on Wednesday afternoon, though the level at the same station had earlier reached 1,500, according to data from the Delhi Pollution Control Committee of the capital territory's government. The WHO guideline is 50 micrograms per cubic metre averaged over 24 hours. Diesel fumes and the burning of rice straw in Punjab have contributed to Delhi's latest cloud of air pollution, which has been exacerbated by lack of wind to blow the smoke away and high levels of moisture in the air. "Current levels of air pollution are high and extremely toxic," said the CSE in a statement, noting the elevated readings of dust and nitrogen dioxide. Already there is evidence of severe respiratory ailments afflicting people. As the pollution worsened on Tuesday, three Supreme Court judges decided to examine the problem, with one of them calling the situation "alarming." Delhi's air improved sharply after 2001 when the engines of public transport vehicles were converted to use compressed natural gas rather than diesel, but the purchase since then of thousands of private vehicles using subsidised diesel has caused a further deterioration. Environmental groups have called for higher taxes on private cars and the tripling of the city's bus fleet of about 6,000.