Air Pollution: A recent study has revealed that between 2015 and November 2025, the air quality in any major city of India was not recorded at ‘safe level’. During this entire period, Delhi remained the most polluted city in the country. This analysis was released by ‘Climate Trends’ (Delhi-based climate research organization) on Friday (28 November) titled ‘Air Quality Assessment of Major Indian Cities (2015-2025)’.
The latest analysis shows that among 11 cities, Delhi had the worst air quality between 2015 and November 2025. The annual average AQI level in the national capital was highest (above 250) in 2016 and has seen a decline since 2019. Although it is still far from the safe level. AQI will be 180 in 2025. After Delhi, Lucknow, Varanasi, Ahmedabad and Pune are next, where AQI levels remained high for a long time. “Lucknow and Varanasi started out at extremely high levels (often above 200). Although both cities have shown steady improvement since 2019, their AQI values will remain above healthy limits until 2025,” the analysis said.
Air quality levels are higher in northern cities – such as Delhi, Lucknow and Varanasi – compared to western and southern cities – such as Chennai, Chandigarh, Visakhapatnam, Mumbai and Bengaluru – especially during winter due to the region’s geographical location. The problem is that these northern cities are landlocked from all sides, because the Indus-Gangetic plain is surrounded by the Himalayas. Due to this the pollutants get trapped and cannot spread. Additionally, the analysis said, “Dense urban structures within cities create additional ‘surface roughness’, a frictional effect that further slows wind speed and limits dispersion.”
The situation is even worse in winter
Rain during the summer monsoon and strong westerly winds help disperse pollutants, but the situation becomes worse in winter. Delhi is particularly affected during this period because it is located in the middle of a vast, flat valley surrounded by the Himalayas to the north. The analysis said, “During winter (December-February) the air in the planetary boundary layer (the lowest part of the atmosphere) is thin because cold air is denser near the Earth’s surface. Cold air becomes trapped beneath the warm air above, forming a kind of atmospheric ‘lid’. This phenomenon is called winter inversion. Since vertical mixing of air occurs only in this layer.” “It happens inside, so the emitted pollutants do not get enough space to spread into the atmosphere.”





























