The air quality during Diwali varies significantly across cities in India, with northern cities typically experiencing higher pollution levels than those in the south. Recent data from the Central Pollution Control Board shows a significant worsening of the average Air Quality Index (AQI) in 10 out of 11 major cities across India in the week following Diwali, compared to the week before. The most pronounced increases were observed in north Indian cities.
The AQI is a key metric used to indicate the air quality in a specific location, reflecting the concentration of pollutants such as particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), and ozone (O3). As the concentration of these pollutants increases, the air quality deteriorates, leading to higher AQI levels and poorer air quality.
North Indian cities saw the most substantial increases in average AQI in the week after Diwali. For instance, Delhi’s average AQI rose from 295 (Oct 24-Oct 30) to 353 (Oct 31-Nov 6), Jaipur went from 196 to 243, and Patna jumped from 126 to 232.
In contrast, southern cities recorded much lower air pollution. Vijayawada’s average AQI increased only slightly from 73 to 74, while Thiruvananthapuram went from 41 to 84. Chennai even witnessed a minimal decline from 108 to 107 during the same period.
Key reasons
On Diwali (October 31), an analysis of the top 50 cities with the highest air pollution, ranging between 210 and 230 AQI, reveals a stark regional disparity. Approximately 37 of these cities were in North India, while 10 are from western states, and only three from southern states.
Gufran Beig, Chair-Professor at the National Institute of Advanced Studies, highlighted factors such as landscape, population density, and temperature differences as key reasons for higher pollution levels in North India compared to the South. “Winter arrives earlier in North India, and as temperatures cool, wind speeds decrease, causing pollutants to accumulate and intensify air pollution levels,” Beig said.
In North India, geographical features, such as the lack of coastal breezes and the proximity to large industrial zones, along with the region’s soil composition also tend to trap pollutants in the air during the winter months. As a result, the burning of firecrackers during Diwali worsen the already poor air quality in this region, leading to extremely high AQI levels.
Metro cities
On Diwali day , among five major metro cities, Chennai and Bengaluru are the only two cities that registered higher air pollution than last year, with slight increases in AQI. Delhi, Chennai, and Mumbai recorded the highest air pollution levels among the metros, with AQI of 339, 213, and 169, respectively.