Delhi still world’s most polluted capital

Delhi’s air quality improved by approximately 15% between 2020 but it still ranked as the 10th most polluted city in the the world and the most polluted capital, followed by Dhaka ( Bangladesh).The study measured the concentration of poisonous PM2.5.

According to the World Air Quality Report, 2020, released by the Swiss air technology company, IQAir. Besides Delhi, the 21 other Indian cities among the 30 most polluted cities in the world are Ghaziabad, Bulandshahar, Bisrakh Jalalpur, Noida, Greater Noida, Kanpur, Lucknow, Meerut, Agra and Muzaffarnagar in Uttar Pradesh, Bhiwari in Rajasthan, Faridabad, Jind, Hisar, Fatehabad, Bandhwari, Gurugram, Yamuna Nagar, Rohtak and Dharuhera in Haryana, and Muzaffarpur in Bihar.

As per the report, the top most polluted city is Hotan in China followed, Ghaziabad is the second most polluted city in the world


Fine particulate matter (PM2.5) is an air pollutant that is a concern for people’s health when levels in air are high. The term fine particles, or particulate matter 2.5 (PM2.5), refers to tiny particles or droplets in the air that are two and one half microns or less in width. Like inches, meters and miles, a micron is a unit of measurement for distance. There are about 25,000 microns in an inch.

Particles in the PM2.5 size range are able to travel deeply into the respiratory tract, reaching the lungs. Exposure to fine particles can cause short-term health effects such as eye, nose, throat and lung irritation, coughing, sneezing, runny nose and shortness of breath.

There are outdoor and indoor sources of fine particles. Outside, fine particles primarily come from car, truck, bus and off-road vehicle (e.g., construction equipment, snowmobile, locomotive) exhausts, other operations that involve the burning of fuels such as wood, heating oil or coal and natural sources such as forest and grass fires. Fine particles also form from the reaction of gases or droplets in the atmosphere from sources such as power plants. These chemical reactions can occur miles from the original source of the emissions. Because fine particles can be carried long distances from their source, events such as wildfires or volcanic eruptions can raise fine particle concentrations hundreds of miles from the event.

The air quality index (AQI) is an index for reporting air quality on a daily basis. It is a measure of how air pollution affects one’s health within a short time period. The Environmental Protection Agency (EPA) calculates the AQI for five major air pollutants, for which national air quality standards have been established to safeguard public health.

  • 1. Ground-level ozone
  • 2. Particle pollution/particulate matter (PM2.5/pm 10)
  • 3. Carbon Monoxide
  • 4. Sulfur dioxide
  • 5. Nitrogen dioxide

The higher the AQI value, the greater the level of air pollution and the greater the health concerns. AQI quickly disseminates air quality information in real-time.

Every day monitors record concentrations of the major pollutants. These raw measurements are converted into a separate AQI value for each pollutant

Air Quality Index Categories

Good (0–50) – Minimal Impact

Satisfactory (51–100) – May cause minor breathing difficulties in sensitive people.

Moderately polluted (101–200) – May cause breathing difficulties in people with lung disease like asthma, and discomfort to people with heart disease, children and older adults.

Poor (201–300) – May cause breathing difficulties in people on prolonged exposure, and discomfort to people with heart disease

Very Poor (301–400) – May cause respiratory illness in people on prolonged exposure. Effect may be more pronounced in people with lung and heart diseases.

Severe (401-500) – May cause respiratory issues in healthy people, and serious health issues in people with lung/heart disease. Difficulties may be experienced even during light physical activity.


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