Top World's Most Polluted Megacities

•  Recent report of WHO on air pollution has confirmed that Delhi's pollution has gone from bad to worse. World Health Organisation (WHO) has declared Delhi's air to be the worst among the world's megacities.
• 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.
• Within India, the smaller cities of Gwalior and Allahabad measured the worst levels of ambient air pollution at PM2.5 levels of 176 µg/m³ and 170 µg/m³ respectively. A significant portion of northern India falls in a zone with “critical” air pollution-reporting PM2.5 levels of over 70 µg/m³ in the WHO’s mapping of air pollution and population.
• 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.
• 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.

Analysis:

• 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.
• In 2012, with one million deaths, China reported the highest toll from PM2.5 and PM10 pollution. At the time, India followed, reporting 621,138 deaths, nearly 10% of the global toll (6.5 million deaths) associated with outdoor and indoor air pollution.
• However, between 2011 and 2015, in a comparison of megacities with population above 14 million, Delhi’s ambient air-pollution levels were worse than Beijing and Shanghai.
• Human body, however, isn’t as good at blocking PM 2.5. These particles are small enough to bypass your respiratory system’s defenses, getting into lungs, where they can even penetrate the bloodstream. That’s when they cause all manner of mayhem. People who live in high PM 2.5 cities have more heart attacks, depressed lung function, worse asthma, and overall die younger than people who breathe clean air. Indices that score air pollution in cities typically give more weight to PM 2.5 than PM 10 levels.

By: Vishal