Pollution levels rising post-lockdown in cities in south India

Air quality management requires regional approach to implement clean air action plans, says CSE (Image: Pixy)
Air quality management requires regional approach to implement clean air action plans, says CSE (Image: Pixy)

An analysis was done by the Centre for Science and Environment (CSE) of winter pollution (until January 26, 2021) in India’s five southern states - a vulnerable but poorly monitored region from the air quality perspective. It indicates that while particulate concentration reduced during the lockdown, it spiked with the onset of winter. The study found that the trapping of winter pollution is quite high -- especially in inland cities, even when the atmospheric conditions here are different from that of the Indo-Gangetic Plains in the northern region.

The analysis is a part of an air quality tracker initiative based on changing air quality trends in different regions of the country sought to understand the impact of 2020 lockdown. It also looks at the lowering of the regional influence on local air quality, and deeper seasonal patterns. 

The analysis is based on publicly available granular real-time data (15-minute averages) from the Central Pollution Control Board’s (CPCB) official online portal Central Control Room for Air Quality Management. 

Real-time data from 36 cities were accessed, and 21 cities were selected for the analysis because real-time data is available for these cities for the whole of 2020. CSE has analysed data recorded by air quality monitoring stations in Bengaluru, Chennai, Hyderabad, Kochi, Thiruvananthapuram, and one station each in rest of the cities under the Continuous Ambient Air Quality Monitoring System (CAAQMS) of CPCB. Weather data for Bengaluru, Chennai, Hyderabad, Thiruvananthapuram, and Visakhapatnam was sourced from the weather stations of India Meteorological Department (IMD) located at the airports in each city. This air quality trend analysis does not include an investigation of local sources of pollution. 

Key findings

Higher PM2.5 levels is a typical and predictable winter trend when continuous emissions from local sources including vehicles, industry, and construction get trapped due to meteorological changes.

While several bigger cities have witnessed a reduction in annual trends in PM2.5, smaller towns and cities have experienced an increase. The 2020 average PM2.5 level in many inland cities in the Deccan Plateau has climbed up to breach the average concentration recorded in 2019. Chikkaballapur in southern Karnataka is the worst performer with 3.9% increase from 2019 level. Tirupati has registered a 1.8% increase. The maximum improvement is noted in Chennai which closed 2020 with a 30% lower PM2.5. Amravati at 24%, Bengaluru at 19%, Visakhapatnam at 16%, and Hyderabad and Rajamahendravaram at 14% are the other best performers in the pool.

The average level of PM2.5 has been lowest during this summer and monsoon due to the lockdown but could not prevent the winter spike. The overall PM2.5 average this summer and monsoon has been predictably lower compared to the previous year largely because of the unprecedented economic disruption during the summer lockdown and phased unlocking. But the reopening of the economy coinciding with the onset of the winter trapping of pollution made PM2.5 levels rose to start in October.

Andhra Pradesh cities were most polluted in the region with Visakhapatnam, Amravati, and Rajamahendravaram being only cities with a weekly average exceeding 100 μg/m3. Mysuru was the cleanest city with its worst weekly average only rising to 33 μg/m3. The transient change of the lockdown phases could not be sustained without the systemic changes needed to control pollution from vehicles, industry, power plants, and waste. 

Average December PM2.5 level has been considerably higher in inland cities this year: December this year was dirtier across most inland cities in the peninsula. The PM2.5 average this December was worst in Andhra Pradesh with 69% higher in Visakhapatnam, 66% in Tirupati, 43% in Rajamahendravaram and 34% in Amravati compared to December 2019. Karnataka cities recorded dirtier December as well with 33% higher in Chikkaballapur and 8% in Bengaluru. Hyderabad’s December was 7.5% dirtier in 2020 compared to 2019. Chennai and Thiruvananthapuram buck the trend recorded registered 16% and 5% cleaner December respectively compared to 2019.

Air quality gets more toxic with the onset of winter -- the share of tinier PM2.5 in the PM10 increases. Interestingly, during the lockdown, when the overall suspended coarser particles had settled down reducing the PM10 levels, the PM2.5 had also come down. Bengaluru and Hyderabad have relatively high PM2.5 percentage throughout the year but their monthly peaks are lower relative to coastal metro cities. The share of PM2.5 in PM10 in Chennai has been identical range as registered in Delhi in 2020 though overall levels are lower. 

Diwali is an issue in southern cities as well: Thiruvananthapuram had dirtier Diwali night in 2020 compared to 2019. 

Hyderabad and Visakhapatnam had earlier start of bad air days in 2020 winter. The rolling weekly average rose over the 24hr standard or 60 μg/m3 in Visakhapatnam on October 23 (9 days earlier), and Hyderabad on October 25 (14 days earlier). This winter overall has been 34 per cent dirtier in Visakhapatnam, 7 per cent in Hyderabad, and 9 per cent in Thiruvananthapuram. Bengaluru registered no change in the seasonal average while Chennai was 20 per cent cleaner. The rolling weekly average didn’t breach the standard in Bengaluru, Chennai and Thiruvananthapuram. 

The number of days with PM2.5 concentration meeting standard was considerably lower this winter in Hyderabad and Visakhapatnam; Bengaluru, Chennai and Thiruvananthapuram saw lesser bad air days.

Cyclical ups and down of pollution this winter is less volatile – showing slower rise and fall than previous winter. This inelastic behaviour of PM2.5 levels in southern cities is looking more volatile during this winter with frequent quicker rise and drop. This can be the impact of meteorology. 

Even with comparatively cleaner air during this year, most cities recorded daily spikes similar to those observed in 2019. CSE has compared the annual averages and peak 24hr averages in these southern cities between 2019 and 2020. This shows that the smaller towns even with much lower annual average levels of PM2.5 have experienced almost the same or higher maximum daily levels during winter when the entire region got air locked. Andhra Pradesh cities have relatively highest daily peak compared to the rest. 

A combination of the reopening of the economy and changing meteorology is responsible for high winter pollution levels. 

“This analysis has dispelled the myth about safer air in the south compared to other regions. Health impacts are nearly equally bad. Complacency cannot slow down the action. Despite the dramatic reduction in air pollution during the lockdown, pollution has bounced back across the region post-lockdown unmasking the high impacts of local and regional pollution. This demands quicker regional reforms to curb pollution from vehicles, industry, power plants and waste burning to further bend the air pollution curve on a regional scale. This demands speed and scale of action,” says Anumita Roychowdhury, CSE’s executive director in charge of research and advocacy.   

This detailed data analysis shows that air pollution is a south Indian problem as well. This requires quicker reforms and action in key sectors of pollution – vehicles, industry, power plants and waste management -- to control winter pollution and further bend the annual air pollution curve. 

“Winter is not as harsh in the southern cities. Therefore, the impact of inversion is expected to be limited -- yet pollution build-up has been noted. Even though the average level of PM2.5 for the summer and monsoon months in 2020 is considerably lower than the previous year due to the summer lockdown, the PM2.5 levels this winter have risen beyond that in 2019 in most of the monitored cities, Chennai and Thiruvananthapuram being the only exceptions. The region cannot rely only on the natural advantage of warmer winters and sea breeze to avoid bad air,” says Avikal Somvanshi, programme manager in CSE’s Urban Lab team of the Sustainable Cities programme.

This analysis bears out the need for deeper clean air action in the regions of southern India that otherwise is considered less polluted than the northern belt. But the region will have to work harder to meet not only the national ambient air quality standards but also aspire to meet the health-based guidelines of the World Health Organisation to reduce the public health risk.  

Says Roychowdhury: “It is clear that the region has to take forward its wins so far and raise the level of ambition to drive action across all key sectors of pollution and in the entire region. Enforce power plant standards across the state, minimise the use of coal and other dirty fuels in the industry while improving industrial emissions control systems, scale-up public transport and vehicle restraint measures, and manage waste to have a zero waste and zero landfill strategy.”

To access the complete CSE analysis click here