Three cities from the National Capital Region — Ghaziabad, Gurgaon and Delhi — were among India’s five most polluted cities last year, the Central Pollution Control Board (CPCB), the country’s apex pollution monitoring and control body, said on Wednesday.
Ghaziabad, with an average air quality index (AQI) of 258, topped the list. Gurgaon was close behind with an AQI of 247, and Delhi ranked fourth at 228. Noida, Faridabad and Alwar — other heavily polluted cities in the NCR — ranked 8th, 11th and 12th. The CPCB rated Thiruvananthapuram as the city with the cleanest air with an AQI of 64.
The list was prepared based on annual average Air Quality Index values from 51 cities across India in 2017. According to the CPCB report published with the list, an AQI of 0-50 is “good”, 51-100 is “satisfactory”, 101-200 is “moderate”, and 201-300 is “poor”. In November, the AQI in Delhi was above 400, or “severe”, for a week. The city was enveloped in a toxic haze that forced authorities to take drastic measures such as closing schools, hiking parking charges and declaring a public health emergency.
“The cities of north India are all landlocked,” said D Saha, the head of the air quality laboratory at CPCB. “Air quality in these cities depends heavily on weather conditions. If the wind is strong and it gets a clear passage and ventilation then pollution level drops. The entire Indo-Gangetic plain is prone to dust pollution.”
Mukesh Khare, a professor of environmental engineering at the Indian Institute of Technology, Delhi, suggested “unplanned urban sprawl” was also to blame for the tendency of pollutants in the capital not to be flushed out by wind.
Delhi’s high ranking comes despite the fact that the city enjoyed relatively cleaner air in 2017 than 2016, when it was shrouded in its worst smog in at least 17 years.
AQI is calculated based on the quantity of materials such as particulate matter and gases, including SO2, NO2 and ammonia, found in the air. The CPCB’s list features the average AQI values in 2017 from the 51 cities across India.
Cities such as Kolkata, with an AQI of 106, Mumbai, with 107, and Chennai, with 95, enjoy much cleaner air than Delhi or any other city in north India.
“This doesn’t mean that Kolkata, Mumbai and Chennai have fewer sources of pollution,” said Vivek Chattopadhyay, the senior program manager of the air pollution control wing at the Centre for Science and Environment. “They remain cleaner mainly because of favourable meteorological conditions such as strong winds.”