Delhi and Kolkata are the two most polluted cities in the world: Report

• Delhi and Kolkata are ranked highest in pollution due to fine particulate matter, according to a new report on air quality and health in cities.
• India’s financial capital Mumbai takes the 14th position on the list of most-polluted cities based on fine particulate matter.
• The report's data analysis from 2010 to 2019 revealed "strikingly different" global exposure patterns for the two main air pollutants – fine particulate matter (PM2.5) and nitrogen dioxide (NO 2).

India is home to the two most polluted cities in the world. In the latest report on the air quality and health in cities around the world, Delhi and Kolkata are ranked highest in pollution due to fine particulate matter, a significant air pollutant. India’s financial capital Mumbai takes the 14th position on this list.
Air Quality and Health in Cities, a State of Global Air report was released on Wednesday. The report examines pollution and its effects on more than 7,000 cities worldwide, focusing on two of the most dangerous pollutants: fine particulate matter (PM2.5) and nitrogen dioxide (NO 2).
When PM2.5 levels were compared, Delhi and Kolkata were found to be the top two most-polluted cities in the world, with an average annual exposure (relative to population) of 110 μg/m3 for Delhi and 84 μg/m3 for Kolkata. The unit μg/m3 stands for microgram per cubic metre.

NO2 Vs PM2.5

The report also compared NO2 levels across the 7,000 cities. No Indian city appeared on the list of the top 10, or even top 20, most polluted cities based on N02 levels. With an average annual exposure of 41 μg/m3, Shanghai is the most-polluted city on this list. The report states that Delhi, Kolkata, and Mumbai had average NO2 concentrations of 20 to 30 μg/m3.
PM2.5 and NO2 are two of the most prevalent air pollutants in cities and urban areas worldwide. PM2.5 is made up of airborne, inhalable particles less than 2.5 micrometres (μm) wide and released into the atmosphere by burning fossil fuels, and from factories, industries, car engines, fires, construction site dust, etc.
NO2 is formed when there is combustion of fossil fuels including coal, gas and oil especially fuel used in cars.
Analysis of data from 2010 to 2019 has revealed "strikingly different" global exposure patterns for the two main air pollutants, the report said. Although cities in low- and middle-income countries typically experience higher levels of PM2.5 pollution, NO2 exposure is high in both high- and low-income cities.
Exposure to such hazardous pollution particles can cause numerous illnesses, including cancer, strokes, and heart and respiratory conditions.
The State of Global Air is a collaboration between the Health Effects Institute and the Institute for Health Metrics and Evaluation’s Global Burden of Disease project.