For the western Indian states of Maharashtra and Gujarat, the winter of 2022-23 had been the most polluted in the last four years – says a new analysis by Centre for Science and Environment (CSE) of the region’s winter air quality (PM2.5) trends. The analysis, done for the period October 1, 2022 to February 28, 2023, has been carried out by CSE’s Urban Lab. In these states, winter pollution typically sets in during late November and early December, when the cooler and calmer conditions trap local pollution.
“The fact that the big cities as well as smaller towns have experienced the rise in winter PM2.5 levels points to the rapid spread of the air pollution problem in this region. This is evident in both the seasonal average and the peaks. While local pollution is increasing in these rapidly motorising and developing cities, the regional influence is further aggravating the challenge. This is overpowering the advantage of natural ventilation of the coastal climate. This demands immediate roadmap to control pollution from the key sources across the region,” says Anumita Roychowdhury, executive director, research an advocacy, CSE.
“While in absolute terms Gujarat has a higher pollution level, it is rising faster in Maharashtra. Most polluted locations in the region are located in Mumbai and Navi Mumbai. Vapi and Surat are among the most polluted locations in Gujarat. Nagpur registered the highest increase in pollution with a 105 per cent rise compared to the previous winter,” says Avikal Somvanshi, senior programme manager, Urban Lab, CSE.
This analysis is part of the third edition of Urban Lab’s Air Quality Tracker Initiative which was started in the winter of 2020-21. This analysis is based on the real time data available from the current working air quality monitoring stations in these two states. A huge volume of data points have been cleaned and data gaps have been addressed, based on USEPA methods, for this analysis. Winter here is defined as the period between October 1, 2022 and February 28, 2023. Winter average is based on the mean of daily averages where continuous data is available since 2019.
The analysis covers 58 continuous ambient air quality monitoring stations (CAAQMS) spread across 17 cities in two states:
- Gujarat: stations in Ahmedabad, three in Gandhinagar, and one each in Ankleshwar, Vapi, Vatva, Nandesari and Surat
- Maharashtra: 21 stations in Mumbai, four in Navi Mumbai, eight in Pune, two in Chandrapur, and one each in Aurangabad, Kalyan, Nagpur, Nashik, Solapur and Thane.
Says Somvanshi: “Even though there are multiple real time monitors in a few cities of these states, many could not be considered for long term analysis due to data gaps and lack of quality data. In several cases, the real time monitors have been set up recently and, therefore, long term data is not available.”
The key findings of the CSE analysis
Winter average of PM2.5 in the cities in this region was highest in the last four years: The average PM2.5 concentration across cities in the west stood at 69 microgramme per cubic metre (µg/m³) this winter. It is 10 per cent higher than the mean of previous three winter seasons (October to February). Daily peak for the region this winter happened on October 24, 2022 (day after Diwali) when the level was 127 µg/m³. It was 25 per cent higher than the mean of the previous three winter peaks.
Fifteen cities that have been considered from the western states for assessment of the regional trend include Ahmedabad, Ankleshwar, Gandhinagar, Nandesari, Vapi, Vatva, Mumbai, Navi Mumbai, Pune, Aurangabad, Chandapur, Kalyan, Nasik, Nagpur and Solapur.
Most polluted winter in the last four years: The average winter pollution level in the cities of Maharashtra rose by 13 per cent compared to the mean of previous three winter seasons. Winter pollution has been rising in Maharashtra on a yearly basis and stood at of 66 µg/m³ this winter.
In absolute terms, Gujarat was the more polluted of the two states, with a winter average of 73 µg/m3. Gujarat registered an increase of 6 per cent compared to the mean of previous three winters. Winter pollution was on a decline in Gujarat since 2019, but it spiked up this winter.
Peak pollution growing faster in Gujarat, but is a problem in Maharashtra as well: Gujarat had its daily peak of PM2.5 at 158 µg/m3 on October 24, 2022. This was the highest regional peak in the last four years and was 19 per cent higher than the mean of the previous three winter peaks.
Maharashtra’s daily peak PM2.5 happened much later in the season, on December 2, 2022. Maharashtra’s daily PM2.5 peak stood at 112 µg/m3, which is marginally lower than the 2021-22 winter peak but 10 per cent higher than the mean of the previous three winter peaks.
Regional influence of pollution is sharply evident in synchronised spread of winter pollution across the cities: Worsening of air quality starts mid-October across western India in a synchronised fashion as weather starts to cool down and winds slow down. But the analysis is hampered by poor data quality among the stations in the region. Data for 96 days is missing from stations in Pune, while in Nandisari data of 68 days is missing. There are large gaps in data from other stations as well.
Pollution hotspots and cleaner cities: Navi Mumbai and Vapi are the most polluted cities in these states. The winter average PM2.5 level in Vapi was 128 µg/m³. In Navi Mumbai, it was 107 µg/m³; Surat had a level of 103 µg/m³.
Gandhinagar in Gujarat was the least polluted city with PM2.5 average of 45 µg/m³. Solapur in Maharashtra also has a seasonal average of 45 µg/m³ but due to excessive missing data (36 days of missing data), this cannot be said with certainty. Same goes for the cities of Nandesari and Pune which have a high quantum of missing data.
Nagpur followed by Navi Mumbai registered the highest increase in winter pollution: Nagpur in Maharashtra was the worst performer and registered an increase of 105 per cent compared to the preceding winter. It was followed by Navi Mumbai with a 59 per cent increase. Winter pollution level in Vapi this season has been 38 per cent higher than the mean of previous three winters.
However, Kalyan in Maharashtra showed the most improvement in air quality this season (23 per cent) compared to the corresponding period in the previous year. It is followed by Pune with 19 per cent, Ankleshwar with 18 per cent, Ahmedabad with 10 per cent and Vatva with 5 per cent improvement in PM2.5 levels compared to the previous year.
Most polluted locations are in the Greater Mumbai region: There is also a wide variation in pollution concentration among the monitoring locations of these states. Navi Mumbai’s Sector 19A monitoring station was the most polluted location among the cities of the two states with PM2.5 averaging at 164 μg/m³. Vapi’s monitoring station at GIDC was the second most polluted location.
Mumbai’s monitoring stations at Deonar, Bandra-Kurla Complex, Mazgaon, Navy Nagar, Chakala and Vile Parle West make up six of the 10 most polluted locations in the two states. Surat in Gujarat also features among these 10 locations.
Multi-pollutant challenge — increasing levels of nitrogen dioxide (NO2) during November and December: In 2022, there was a significant increase in the amount of NO2 concentration during November and December compared to October. NO2 comes entirely from combustion sources and significantly from vehicles. Kalyan in Maharashtra registered the greatest increase – three times the maximum build-up of NO2 between October and December. Nagpur and Nandesari each registered a 2.3 times increase.
In absolute concentration, Ahmedabad registered the highest NO2 average of 104 µg/m³. It is followed by Kalyan with 89 µg/m³ and Navi Mumbai with 61 µg/m³. The lowest NO2 levels were recorded by Nandesari with 4 µg/m³ and Vapi with 7 µg/m³.
Diwali pollution increased in several cities: The pollution level on Diwali night (8 pm to 8 am) in cities shot up by 1-5.9 times the average level recorded seven nights preceding Diwali (see graph on this in the complete analysis report). Ahmedabad experienced a 5.9 times higher PM2.5 level on Diwali night at 393 µg/m³. It is followed by Chandrapur in Maharashtra with 4.6 time’s higher PM2.5 concentration. Mumbai and Nagpur had the least polluted Diwali night in the region, with 70 and 75 µg/m³ respectively, followed by Nashik with 85 µg/m³.
Step up the action
Says Roychowdhury: “The rapidly growing cities of the western states of Maharashtra and Gujarat that were hitherto not so much under the scanner for growing air pollution problem, are increasingly coming under the spotlight. Winter pollution is indicative of the growing local problem. As soon as the weather turns adverse with cool and calm conditions, the high local pollution gets trapped and spirals.”
“This demands urgent and aggressive scaling up of the multi-sector action plan to control pollution from vehicles and transport, industries, open burning of waste and landfill fires, use of solid fuels in households, construction, and dust sources,” she adds.
(Report sent by Pratyusha Mukherjee)
(A CSE Media Briefing)
