New Delhi: Delhi's increasing pollution levels have been a matter of concern for a long time. Even though awareness campaigns and ideas for its control have done their share of rounds, people are yet to witness any change.

If anything, Delhi's air pollution has gone from bad to worse and fresh air has become a thing of the past. Confirming this, the World Health Organisation (WHO) has declared Delhi's air to be the worst among the world's megacities.

IndiaSpend's #breathe network of air-quality sensors reported fine-particulate-matter (PM2.5) levels were almost four times above daily safe levels, on average, for the seven-day period from September 22 to 28, 2016.

For long-term exposure, these 24-hour levels are nearly 11 times above the WHO health standards.

The monsoon season, in this regard, brought with it better quality of air, since rain and wind diminished the impact of pollutants. But with the season changing, three of our five sensors in the National Capital Region (NCR) registered "poor" to "very poor" air-quality levels from September 22 to 28, meaning prolonged exposure affects healthy people and "seriously impacts" those with existing disease.

Delhi recorded a PM10 level of 229 µg/m³, followed by Cairo with 179 µg/m³ and Dhaka with 158 µg/m³ -- the top three megacities with the most polluted air globally. Beijing and Shanghai were sixth and seventh on that list.

India's capital was the only megacity to record a PM10 level above 200 µg/m³, exceeding the WHO air quality standard of 20 µg/m³ by more than 900 per cent.

The WHO's new air-quality model, it's most comprehensive yet, is based on information from satellite measurements, air-transport models and ground-station monitors for more than 3,000 urban and rural areas across the world. It analyses this with population data in a grid pattern area of 10 sq km. It was developed by the WHO in collaboration with the University of Bath and confirms that 92 per cent of the world's population lives in places where air quality levels exceed WHO limits.

11,297 persons per sq km in Delhi at risk.

Some three million deaths every year are linked to exposure to outdoor air pollution, according to the WHO. Nearly 90 per cent of air-pollution-related deaths occur in low- and middle-income countries, with nearly two out of three occurring in WHO's Southeast Asia region (of which India is a part) and the Western Pacific region.

(With IANS inputs)