Toxic Tales

South Asia is home to the most polluted regions in the world. Fifteen of the world’s 20 worst polluted cities in 2018 are in India, followed by Lahore and Dhaka.

By Prof. S. Shafiq-ur Rehman | January 2020


At the end of the second decade of the 21st century, the review of environmental data indicates that the world we live in is becoming increasingly dangerous for human health at large and sensitive groups in particular. Almost everything that surrounds us, such as air, water, soil, and often food items we consume, are polluted because of our own actions making large populations highly vulnerable to adverse health impacts in the form of protracted ailments and fatalities. Besides, some air pollutants are directly responsible for global warming and climate change that trigger all sorts of natural disasters unleashing death and destruction on human beings and affecting the rest of the ecosystem.

The Air Quality Index refers to the numerical values reflecting concentration of major air pollutants that include particulate matter, ground level ozone, sulfur dioxide, nitrogen dioxide and carbon monoxide per cubic meter of air. Among these pollutants, particulate matter and ground level ozone are considered to have the highest impact and affect everyone. The AQI categorizes air into six categories, i.e. Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very unhealthy and Hazardous. Higher index value means higher pollution level, hence higher risk to human health. According to WHO, an annual mean of air quality guidelines of 10 µg/m3 is the safe limit for particles with a diameter of 2.5 microns or smaller (PM≤2.5) while the safe limit for a 24-hour mean is 25 µg/m3. The safe limit of annual mean for PM≤10 is up to 20 µg/m3, while the 24-hour mean is 50 µg/m3. Common ailments associated with bad quality air include chronic obstructive pulmonary disease (COPD), hypertension, strokes, lung cancer, pneumonia, cardiac diseases, dementia, chronic renal diseases and type-2 diabetes.

On the basis of AQI values, countries and selected cities are ranked from most polluted to least polluted, indicating public health risks from highest to lowest levels for the people residing in these countries and cities. The latest country rankings indicate that 15 of the top 20 most polluted countries are in Asia. In descending order, the first ten countries are Bangladesh, Pakistan, India, Afghanistan, Bahrain, Mongolia, Kuwait, Nepal, UAE and Nigeria. Other Asian countries among the top 20 most polluted are Indonesia, China, Uzbekistan, Vietnam, Sri Lanka, and Kazakhstan.

The most polluted cities the world is also alarming in the Asian context. Seven Indian, two Pakistani and one Chinese city constitute the top 10. Fifteen Indian cities, two Pakistani, two Chinese, and one Bangladeshi city account for the top 20, whereas, 25 Indian and 22 Chinese cities are included in the top 50 most polluted cities in the world. While Faisalabad and Lahore rank at number 3 and 10 from Pakistan, Gurugram, Ghaziabad, Faridabad, Bhiwadi, Noida, Patna, and Lucknow are the Indian cities in the top 10. Delhi ranks at number 11, Agra at number 16 and Dhaka at number 17. The highest air quality index in the world’s top 10 most polluted cities remains predominantly unhealthy to very-unhealthy, typically from October to January.

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The writer is former Chairman, Department of Environmental Sciences, University of Peshawar. He can be reached at srsyed55@gmail.com

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  • January 3, 2020 at 9:33 am
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    Excellent review and analysis of a very serious problem.
    We must act now before it’s too late.

    Reply