Clean Air Toolbox for Cities
4 min readOct 8, 2021

Sandhya Sethuraman, Yuvan Das, and V. Faye McNeill (@vfmcneill,, Columbia University

Particulate air pollution is a countrywide public health problem in India, contributing to 2.5 million premature deaths annually. Sources of PM2.5 across the country vary, but may include vehicle exhaust, power generation agricultural burning and waste burning, and road and construction dust.

Since 2016, India’s Central Pollution Control Board (CPCB) has been expanding their network of ground-based measurements of fine particulate matter (PM2.5). In light of newly available data from this network, we have revisited our previous analysis, “India’s Air Pollution Crisis: By the Numbers” (McNeill and Nunes, HuffPost India 2017).

We have analyzed ground-based PM2.5 data from CPCB instruments in 25 Indian cities in 17 Indian states from January 2019-January 2020. We extracted our data from over 109 sensors, most of which we accessed through India’s Central Pollution Control Board (CPCB). Within the CPCB, we downloaded specific data sets from the Central Control Room for Air Quality Management (CCR). Additionally, we extracted select data sets (e.g., for sensors located at U.S. Diplomatic posts) from OpenAQ. One notable difference from the 2017 analysis was the much greater availability of data and improved spatial coverage for the 2019–2020 period, as PM2.5 monitoring has increased throughout the country. Datasets were collected from: Agra, Ahmedabad, Bengaluru, Brajrajnagar, Chennai, Delhi, Faridabad, Guwahati, Hyderabad, Jaipur, Jodhpur, Kolkata, Lucknow, Ludhiana, Mumbai, Nagpur, Nashik, Patna, Solapur, Thiruvananthapuram, Ujjain, Varanasi, Vijayawada, and Visakhapatnam. 24-hour average data was categorized in terms of the Indian National Ambient Air Quality Standard, the international/U.S. air quality index, and the Indian air quality index, and trends, regional variations, and changes since 2016–17 were analyzed.

The pie charts in Figure 1, prepared following the approach of McNeill and Nunes (2017), represent the proportions of days in each city from January 2019 to December 2019 that fell into three categories, based on the United States’ Air Quality Index.

  • Green — Little to No Risk — PM2.5 levels less than 35.4 µg/m3
  • Yellow — Unhealthy for Sensitive Groups — PM2.5 levels between 34.4 and 55.4 µg/m3
  • Red — Unhealthy — PM2.5 levels above 55.4 µg/m3
Figure 1. Summary of PM2.5 data (CPCB) for January-December 2019, binned by U.S. Air Quality Index categories (see text for legend).

We also categorized the same data following the Indian AQI categories (shown below, Figure 2). Days in green and light green, which correspond to PM2.5 levels of 60 µg/m3 or lower, are within the Indian NAAQS limit (i.e., in attainment).

Figure 2. Summary of PM2.5 data (CPCB) for January-December 2019, binned by India Air Quality Index categories

Similar to what we observed for 2016–2017, this analysis shows that PM2.5 air pollution is a nationwide problem in India. While there is more awareness and media attention regarding the high PM2.5 levels experienced in northern locations in the Indo-Gangetic Plain (especially in Delhi), even coastal and southern cities like Mumbai and Chennai, where the issue has received significantly less attention, experience unhealthy air a significant fraction of the year. However, some good news was revealed by comparing this analysis to the 2017 data: there were more “good” air quality days in 2019–2020 than in 2016–2017 for many locations including Delhi, Kolkata, Bengaluru, Mumbai and Chennai. A multiyear investigation should be conducted in order to confirm this trend.

Finally, we looked into the impact of COVID-19 on PM2.5 pollution across the country. We calculated the percent change in PM2.5 levels during the period March 24-June 1 in 2020, as compared to the same period in 2019 (Figure 3). No significant temperature or precipitation differences existed between the two time periods.

Figure 3. Percent difference in PM2.5 levels for March 24-June 1, 2020, compared to the same time period in 2019.

As a result of the shutdowns, some activities that are generally sources of air pollution — vehicle traffic, pollution from industrial centers — decreased, while other pollution sources , such as agricultural burning, electricity generation, and residential solid fuel burning did not. As a result, PM2.5 levels temporarily decreased to varying degrees across the nation, depending on the local mix of pollution sources, meteorological conditions, etc. While the impact of COVID-19 on air quality was temporary, this data can be used to gain insights into the importance of the affected sources on local air quality. The bluer skies during that time also increased awareness of what might be possible with improved air quality.



Clean Air Toolbox for Cities

Columbia University Clean Air Toolbox for Cities Initiative