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New Delhi, January 19, 2022: Every winter, as inversion leads to smog-filled days and nights across entire north India, the western region of the country -- by contrast -- looks much cleaner. A new analysis of regional air pollution levels, done by Centre for Science and Environment (CSE), says air pollution is rapidly becoming a matter of concern in the western states of Maharashtra and Gujarat as well.
Winter pollution sets in these states during late December and early January when cooler and calmer conditions trap the local pollution, which is high. Even though winter pollution levels in the western region are not as high (as that seen in the Indo-Gangetic Plains) due to its proximity to the sea and improved ventilation, the levels have been seen to be increasing despite the geographical advantages and favorable meteorology, says the analysis.
“This analysis of real time air quality data for the period 2019-2021 shows that the downward dip in pollution that was induced by the lockdown phases of the pandemic in 2020, is changing. Pollution levels are threatening to bounce back – they are already rising in 2021. In many cases, the levels are even higher than in 2019. The number of bad-air days in Mumbai have doubled between 2019 and 2021, while good days are down by 20 per cent. This underscores the urgency of scaling up action across all sectors to prevent further worsening and to arrest the trend in this region,” says Anumita Roychowdhury, executive director, research and advocacy, CSE.
“Even though real time air quality monitoring has begun to expand in these states to provide more up-to-date information on air quality, there are serious concerns around missing data and gaps that makes proper risk assessment difficult. In some stations of Maharashtra and Gujarat, data availability is so low that the trend cannot be assessed. Quality control of data is necessary,” says Avikal Somvanshi, programme manager, Urban Data Analytics Lab, CSE.
This new analysis of real time pollution data is part of CSE’s air quality tracker initiative. The objective of this new analysis is to understand the trends and magnitude of pollution in different regions that have real time air quality monitoring systems. This is an assessment of annual and seasonal trends in PM2.5 concentration for the period January 1, 2019 to January 9, 2022. This analysis is based on the real time data available from the current working air quality monitoring stations. For the analysis, a huge volume of data points have been cleaned and data gaps addressed based on the USEPA (United States Environmental Protection Agency) methodology.
The analysis covers 56 continuous ambient air quality monitoring stations (CAAQMS) spread across 15 cities in two states: Maharashtra -- one station each in Aurangabad, Kalyan, Nagpur, Nashik and Solapur, two in Chandrapur, four in Navi Mumbai, eight in Pune, and 21 stations in Mumbai; and Gujarat -- one station each in Ankleshwar, Nandesari, Vapi and Vatva, four in Gandhinagar, and eight stations in Ahmedabad.
Somvanshi points out that even though there are multiple real time monitors in a few cities of these states, many of them could not be considered for long-term analysis due to data gaps and lack of quality data. Moreover, in several cases, the real time monitors have been set up recently and therefore, long-term data is not available. Several cities of Gujarat have got their real time monitors in June 2021. Many stations in Maharashtra have got their real time monitors in June 2019 and November 2020. Thane station stopped reporting PM2.5 data in early 2019, therefore it could not be included in this analysis.
The key findings
Challenge of data gaps and quality despite automation: Review of data availability from the automated monitoring stations in the region under the CAAQMS programme of CPCB shows major data gaps. Data availability calculated as number of days with adequate PM2.5 data for computation of a valid 24-hour average has been low in five of the 12 cities in the region. For the year 2021 (June to December), there is no data available from Airoli station of Navi Mumbai and Pimpleshwar Mandir station of Thane. Alandi and Hadapsar stations in Pune have offered just 21 and 36 per cent data, respectively, while the Solapur station could produce only 39 per cent.
Among Mumbai stations, Kurla had only 55 per cent data while Malad West came up with 68 per cent. Kalyan and Aurangabad were data-poor as well, with 66 per cent and 43 per cent data availability, respectively. Only one out of eight stations of Pune meets the minimum requirement – Pune’s stations have a data availability of less than 75 per cent.
It is not clear why these stations have such poor data availability despite minimal problems of electricity and internet connectivity in the region. This requires an assessment. In contrast, most stations of Gujarat perform better, with data availability of more than 85 per cent. Only the stations at Chandkheda in Ahmedabad and Nandesari are below the minimum 75 per cent data availability requirement.
Most cities indicate a rising trend in annual PM2.5 levels after an initial drop during 2020 (when there were lockdowns): Nearly all cities in the region show a drop in annual average PM2.5 levels in 2020 -- the year with the maximum number of lockdown phases. But there has been a rebound and a rising trend is visible in 2021. Gujarat’s cities are more polluted than those in Maharashtra. Vatva and Ankleshwar have the most polluted air in the region with the 2021 average of PM2.5 at 67 ug/m3. This is followed by Vapi and Ahmedabad with 2021 annual averages at 54 ug/m3 and 53 ug/m3, respectively.
In Maharashtra, Chandrapur, an industrial city, has recorded levels marginally above the annual standard at 43 ug/m3. Other stations have met the annual standard though all of them are showing a rising trend in 2021 after the dip in 2020. If the real time data is taken as an indicator, in Gujarat, Vatva and Ankleshwar need to reduce their annual average PM2.5 by 40 per cent to meet the PM2.5 standard; Vapi should aim for a 25 per cent reduction, and Ahmedabad Maninagar, 24 per cent.
Despite low annual levels, cities in Maharashtra experience high number of days with ‘poor’ and ‘very poor’ AQI: With 102 days of poor and very poor AQI, Ankleshwar in Gujarat has the unhealthiest days in the region. It is followed by Kalyan with 84 days, Vatva (75 days), and Navi Mumbai (54 days). Vapi has 48 days of poor and very poor AQI -- but, its data is missing for 138 days (mainly for the winter months). Mumbai has registered 42 days of poor and very poor AQI despite meeting the annual standard.
Bad-air days begin to build up in the cities of the western states during the end of December and persist till the end of January. Cities in the Mumbai Metropolitian Region show more pronounced impact of winter pollution compared to cities of other regions. Industrial towns have bad-air days across the year, but there is some clustering during winter (see Graph in complete analysis – Heat map based on days classified as per PM2.5 air quality index for major cities).
Levels during high weekly pollution episodes in winter can be more than double the annual concentration in several cities: During the worst weekly pollution episodes in winter, the PM2.5 concentrations can increase significantly higher than the annual PM2.5 average – about two times high in several cities. During the high pollution episodes, weekly PM2.5 levels can go as high as 139 ug/m3 as recorded in Ankleshwar in December 2021. This winter, so far, the highest weekly level was 133 ug/m3 in Vatva, 117 ug/m3 in Kalyan, 115 ug/m3 in Ahmedabad Maninagar, 109 ug/m3 in Vapi, and 103 ug/m3 in Navi Mumbai. The levels are marginally higher this winter compared to last winter, with Chandrapur being the highest, with a 1.5 times increase compared to previous winters.
Number of bad-air quality days are increasing in Mumbai: Over the years, the air quality in Mumbai seems to be declining. Daily AQI analysis based on 10 oldest stations shows a 20 per cent drop in number of good AQI days in the city between 2019 and 2021 -- while days with poor or very poor AQI have doubled.
South Mumbai has the worst air within the city during winter: In December 2021, the stations in south Mumbai have reported significantly higher PM2.5 levels compared to the rest of the city. Mazgaon with a monthly average of 134 ug/m3 was the most polluted neighborhood of the city, followed by Navy Nagar-Colaba (124 ug/m3), Kurla (101 ug/m3), Vile Parle West (101 ug/m3) and Worli (97 ug/m3). Khindipada at the edge of Sanjay Gandhi National Park in the suburbs with a monthly average of 54 ug/m3 was the least polluted neighborhood. Bandra and Malad West reported low numbers, but the values are not considered valid due to significantly large amount of missing data from these two stations.
Changing ratio of PM2.5:PM10 during different seasons of 2021: The PM2.5/PM10 ratio is a useful indicator to understand the impact (on air quality) of coarse dust as opposed to the tinier dust from combustion sources. Higher share of smaller particles in total particle concentration makes the air more toxic. The indicative ratio for all cities shows there is a seasonal variation. The share of smaller PM2.5 is higher than the coarser PM10 in monsoon and winter. The long-term variation of the PM2.5:PM10 ratio was analysed from weekly data averages for three different seasons: summer (March-May), monsoon (June-October), and winter (November-January).
The PM2.5:PM10 ratio in all the cities of these states has an increasing slope from summer to winter except in Nagpur, which is showing a high percentage of PM2.5:PM10 ratio in summers -- 52 per cent -- and then gradually dropping to 36 per cent in monsoon, which again spikes to 49 per cent in winter (see Graph in complete analysis on changing ratio of PM2.5:PM10 during different seasons of 2021). Mostly, the concentration of PM2.5:PM10 ratio is higher during the winter months (November to January), hovering between 50 to 60 per cent. This is indicative and there can be variations across years. However, this trend is broadly consistent with what has been noted in parts of the country.
In Gujarat, Nandesari has the highest PM2.5:PM10 ratio in all the three seasons with the PM2.5 share as high as 71 per cent in winter. Ankleshwar is showing high percentage of PM2.5:PM10 ratio in winters -- 72 per cent. The highest percentage of PM2.5:PM10 ratio in monsoon was 73 per cent in Nandesari. Overall, in Gujarat, the concentration of PM2.5:PM10 ratio is higher during winters (November to January).
Nashik in Maharashtra recorded the highest percentage of PM2.5:PM10 ratio in winters: 70 per cent. Vapi in Gujarat and Aurangabad in Maharashtra had data gaps for the month in summer and winter seasons. Therefore, these stations have not been included in this analysis.
Winter pollution can be a toxic cocktail of particulates and gases: There is a significant increase in amount of nitrogen dioxide (NO2) in air of all cities of western states during December compared to the previous months of November, October and September. Solapur registered a 4.9 times jump in monthly NO2 level, Navi Mumbai was 3.9 times more, while Aurangabad had a 3.6 times increase; Chandrapur registered a 3 times increase; Vatva, 2.7 times increase; and Mumbai, 2.5 times increase.
In absolute concentration terms, Vatva registered the highest monthly average of 120 µg/m3 for December. This is higher than the 24-hour standard for NO2. It is followed by Solapur (46 µg/m3) and Pune (44 µg/m3). Such high levels are not recorded even in north Indian cities.
Thane showed a dramatic increase in the amount of NO2 in the months of November and October as compared to December. It has missing data for the month September (see Graph in complete analysis on monthly trends in nitrogen dioxide levels). Vapi station in Gujarat is not included in the analysis due to data gaps.
NO2 levels correlate well with traffic peaks in cities: All cities show peaking of hourly NO2 concentration between 6 pm and 8 pm, which coincides with the evening rush hour in cities. Hourly NO2 in Vatva increases 3.4-folds between noon and 7 pm (see Graph in complete analysis on hourly NO2 cycles for December). The NO2 cycle is equally sharp in Nashik and Navi Mumbai with a 2.6-2.2 times increase noted at evening compared to the afternoon. All cities have a morning NO2 peak around 7-8 am, but this is relatively lower than the evening peak. In Pune, Mumbai and Ahmedabad, high NO2 levels persist up till midnight, indicating the presence of pollution from night-time truck movement in these cities.
The way ahead
Says Roychowdhury: “The western region has its own unique challenges and will have to be addressed. Pollution trapping can be high during adverse winter conditions, as the overall pollution levels in cities are high. The region is already experiencing a rebound of pollution after the temporary dip in 2020 due to the pandemic-linked hard lockdown phases. Key industrial towns and clusters are located in these two states that require attention. Maharashtra is among the states with highest number of non-attainment cities under the National Clean Air Programme.”
The CSE analysis recommends stronger multi-sector interventions to reduce pollution in a time-bound manner, meet the national ambient air quality standards, and prevent further worsening of the trend. This requires massive scaling up of the access to clean fuel and technology in industry and power plants, transformation of public transport, walking and cycling at a scale, renewal of vehicle fleet, rapid electrification of new vehicle fleet, amendment of municipal bylaws based on central waste management rules and regulations and scaling up of infrastructure for management and recycling of all waste streams, elimination of solid fuels for cooking, controlling dust from construction sector and adopting greening and afforestation strategy for dust control. “This agenda is non-negotiable to meet the clean air target,” says Roychowdhury.
For more on this or for interviews, please contact Sukanya Nair: sukanya.nair@cseindia.org, 8816818864
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