AQI Data: Clear Difference in AQI Levels Between North & South Indian Cities Observed
Sai Krishna Muthyanolla
November 17, 2023
AQI data from the CPCB indicates that like the trend observed in the case of major cities, there is a clear difference in pollution levels in the cities in the north and south. The pattern seems to be more cyclic in the north with the AQI increasing in the winter months from October to February while there is no such cyclic pattern in the cities in the south or peninsular region.
Previously, Factly published a story on the trends in the Air Quality Index (AQI) reported across the eight Tier-I (large) cities. Analysis of the daily AQI trends across the major cities viz; Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, and Pune from 2015 to 2023 revealed a cyclic pattern, with poorer air quality at the beginning and end of the year. However, cities like Chennai and Bengaluru, with milder winters, showed different patterns. In other words, seasonal variations had a strong influence on the AQI reported as evident in cities’ monthly AQI patterns.
Delhi’s AQI exhibited erratic fluctuations, while Mumbai and Kolkata witnessed increased days with AQI surpassing 200 in recent years. Further, Delhi had limited ‘Good’ air quality days (14 days in 8 years), with days equalling four of the eight years in ‘Poor’ to ‘Severe’ categories. Kolkata followed with days equalling a year of poor air quality days. While cities like Bengaluru never reported severe pollution, Hyderabad and Mumbai had rare instances. Bengaluru stood out with over a year of ‘Good’ air quality days during this period.
In this story, we look at the trends in Tier-II cities which include urban areas that are relatively smaller compared to Tier-I cities, but still substantial in terms of population and economic activity. A total of 53 cities have been considered in the story. These cities were selected based on the criterion of having AQI data available for a minimum of one year. The data used in this story has been taken from Dataful. The dataset presents the data compiled every day (average of 24-hour measurements, taken at 4 PM every day) in AQI reports from the year 2015 to 12 November 2023.
There is clear difference in the AQI patterns reported in north and south Indian cities
Similar to the trend observed in the case of major cities, there is a clear difference in the pollution levels in the cities in the north and south. The pattern seems to be more cyclic in the north with the AQI increasing in the winter months from October to February while there is no such cyclic pattern in the cities in the south or peninsular region.
For instance, in cities like Agra, Kanpur, Lucknow, Noida, Jaipur, Jodhpur, Kota, Nashik, Guwahati, Faridabad, and Patna, the cyclic pattern is clearly evident. At the same time, in south Indian cities like Hubbali, Thrissur, Mangalore, Vishakapatnam, Vijayawada, Kochi, and Coimbatore, there is no such pattern. In Faridabad, Noida, Jodhpur, and Jaipur, not only does the pollution increase between November and December but there is also a spike in the months of April and May as well. However, the increase in the summer months is not as large as that in the winter months in these cities. One reason for this could be the higher temperatures experienced in this region during summer. High temperatures can exacerbate the conditions that lead to increased concentrations of pollutants in the atmosphere.
Many cities have reported an improvement in the air quality, especially in the recent years. One notable improvement is in Varanasi, where the highest AQI reported in 2017 was 500 (Highest Value of AQI- Severe) which gradually dropped to below 400 in 2019. In 2021, the highest AQI reported in the city was 293 which dropped to 216 in 2022. A few other cities that saw a decline in AQI are Moradabad, Lucknow, and Meerut, which also are in Uttar Pradesh.
In cities like Durgapur, Siliguri, and Agra, the number of days with AQI above 400 has declined since 2021 while in Aurangabad and Moradabad, the frequency of days with AQI above 200 has declined. The impact of the COVID-19 lockdown is visible in the AQI reported in the cities of Kochi, Kollam, Thrissur, Nagpur, and Patna where the AQI dropped during the outbreak & lockdown periods. However, it has increased after the restrictions were relaxed in some of these cities.
The AQI has been relatively better in the southern cities. In Kozhikode, the AQI has been less than 100 most of the time while it seldom crossed 200 in Kannur, Kollam, and Thiruvananthapuram. Belgaum and Hubbali, Mangalore and Mysuru have also witnessed only a few instances when AQI crossed 200.
Within a state itself, there is a significant difference in AQI reported among the cities. For instance, Vishakapatnam is more polluted than Vijayawada. While the former consistently recorded AQI greater than 200 since 2016, the latter recorded it only in recent times.
Except for Vishakapatnam and Kalaburagi, no other south Indian city has reported more than 10 days with AQI above 400
The number of days reported in each category of AQI for the selected Tier–II cities is given in the chart below. Except for Vishakapatnam and Kalaburagi, no other south Indian city has reported more than 10 days with AQI in the ‘Very Poor’ or ‘Severe’ categories. On the other hand, Faridabad, Ghaziabad, Lucknow, Noida, Kanpur, Patna, Varanasi, and Agra have had days equalling more than a year of ‘very poor’ or ‘severe’ AQI during this period of about 8 years. Faridabad, Ghaziabad, Noida, and Kanpur recorded more than 125 days each in the ‘severe’ category. While only about one-fifth of the days were reported with ‘good’ or ‘satisfactory’ AQI in these cities, it was around 50% for the cities in central and southern India.
Apart from the weather conditions that have been observed to have influenced the AQI in the various cities analysed, there are numerous other factors that affect the AQI levels. The level of urbanization, industrial activity, transportation, power generation, agriculture activities, and even natural events can affect the air quality. India should work on mitigating air pollution using a comprehensive approach addressing these different causes while also considering the local conditions. Transitioning to cleaner energy sources, improving industrial processes, promoting cleaner transportation, and policies to reduce emissions from various sources, should be considered. There is also a need for better distribution & coverage of air quality monitoring stations as this is highly skewed. Better distribution & increased coverage is important for accurate monitoring.
Featured Image:  Air Quality Index