The world health agency and many other bodies have issued such warnings in the past also after regularly tracking the level of pollutants. The WHO had recently in another report said that the air in most cities is so much laced with carcinogenic substances that over two lakh deaths occur every year from lung cancer caused by pollution. The latest report estimates that over 3.7 million premature deaths may have occurred due to various ailments caused by air pollution in 2012. The medical cost of treatment of diseases is very high. Developing countries, especially China and India, lead in air pollution and their cities are becoming increasingly unhealthy. Some studies have placed India in the worst category.

Many of the 124 Indian cities surveyed by the WHO have unacceptably high levels of dust and smoke in the air. The metropolitan cities were already known to be highly polluted but now the contamination levels are increasing in Tier-2 and Tier-3 cities also. According to the report Gwalior, Raipur, Lucknow and Agra are leading in the presence of dangerous particulate matter in the atmosphere. This may be because these cities are growing fast but the civic authorities are too lax in curbing the collateral impact of such growth on public health. Delhi had once made some progress in cleaning up its air but it has deteriorated now. Cities in south India fare relatively better but they are also in the danger zone. Both indoor and outdoor pollution levels are high.

Increased industrialisation and urbanisation, growth in vehicle population, absence of effective rules to check pollution and poor implementation of rules are the major reasons for the deterioration of air quality. The Air (Prevention and Control of Pollution) Act, 1981, is not considered strong enough to deal with all aspects of the problem. The union environment ministry revised the air quality standards and brought them on par with those in Europe some years ago but there has been little action in implementing the standards. Governments, local institutions and many agencies including corporate bodies have to act together to address the problem. There is greater awareness among the people of the dangers of pollution and this should lead to greater public pressure on the authorities to act effectively