Winter air pollution in cities of southern states is lower than in other regions. Pollution is bouncing back now, though it has not yet hit the pre-pandemic levels
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New Delhi, January 21, 2022: Cities in south India are some of the cleanest in the country when it comes to breathable air, but they still suffer from some influence of winter inversion and, resultantly, elevated pollution levels. The levels increase despite the geographical advantages and favorable meteorology due to the region’s proximity to the sea and improved ventilation – finds a new 2019-2021 analysis of winter air quality in India’s south, done by Centre for Science and Environment (CSE).
In 2020, the annual average levels of PM2.5 had a downward tilt in this region, but in 2021, they have risen in most cities, finds the CSE analysis.
“However, unlike states in other regions of the country, the air quality gains are not completely lost. In most cities, the levels of 2021 are still lower than in 2019. This signals towards early preventive action to prevent further worsening in the coming years. This requires urgent scaling up of across all sectors 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 Karnataka, Hyderabad and Tamil Nadu, 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 at CSE.
This is evident from the new analysis of real time pollution data as part of the air quality tracker initiative of the Urban Data Analytics Lab of CSE. The objective of this new analysis is to understand the trend 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. A huge volume of data points have been cleaned and data gaps have been addressed based on USEPA (United States Environmental Protection Agency) methods for this analysis.
The analysis covers 63 continuous ambient air quality monitoring stations (CAAQMS) spread across 39 cities in five states and one Union territory:
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. Moreover, in several cases, the real time monitors have been set up recently and therefore, long term data is not available -- several cities of the southern region have got their real time monitors in November 2020. Chennai got four out of eight monitors in January 2021. Vijaywada station stopped reporting PM2.5 data after October 2019, and Sanegurava Halli station in Bengaluru stopped reporting PM2.5 data in early 2019.
The key findings
Challenge of data gaps and data quality despite automation in Tamil Nadu and Karnataka -- situation relatively better in Andhra Pradesh, Telengana and Kerela: Review of data availability from the automated monitoring stations in the region under CAAQMS 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 19 of the 39 cities in the region. For the second half of the year 2021 (June to December), data availability at Vijaywada station of Andhra Pradesh, City Railway Station and Sanegurava Halli stations of Bengaluru, Thoothukudi station of Tamil Nadu, and Udupi station of Karnataka has been zero per cent. Coimbatore station of Tamil Nadu, and Kalaburagi and Bidar stations of Karnataka have just 27 per cent, 39 per cent, and 7 per cent data availability, respectively. Velachery and Manali Village stations of Chennai also reported data only for 27 per cent and 36 per cent of days, respectively.
Among Bengaluru stations, Silk Board has only 61 per cent data while Peenya and Jayanagar are with 64 per cent and 68 per cent, respectively. Gummidipoondi station of Tamil Nadu and Central University of Hyderabad are data poor as well, with 49 per cent and 55 per cent data availability, respectively. Only 12 out of 21 stations of Karnataka outside Bengaluru meet the minimum requirement of 75 per cent. It is not clear why these stations have such poor data availability -- this requires additional assessment which is not within the scope of this study.
In contrast most stations of Andhra Pradesh and Kerala perform better as they have data availability of more than 75 per cent: the only station below par is at Plammoodu in Thiruvananthapuram, Kerala.
Many cities show a rising trend in annual PM2.5 levels after an initial drop during 2020: Among all the regions, cities of south India have shown least of a rebound and a rising trend once again in 2021 after a significant drop due to the pandemic lockdowns of 2020. But there is still a rebound and it should be seen as a warning signal. Twenty-two cities have adequate data for both 2020 and 2021 for annual average computation -- 16 of these cities show an increase in their annual PM2.5 averages, while six show further improvement. Kochi has registered doubling of its annual PM2.5 average between 2020 and 2021. Cities that show improvement are Chennai, Kalaburagi, Chikkaballapur, Vijaypura, Chikkmangaluru and Kozhikode.
The industrial town of Gummidipoondi near Chennai in Tamil Nadu had the most polluted air in the region with 2021 average at 46 ug/m3. This is followed by Visakhapatnam and Hyderabad with 2021 annual average of PM2.5 at 44 ug/m3 and 41 ug/m3, respectively. In contrast, all other cities in the southern region have met the annual standard.
Cities of Andhra Pradesh and Telangana have the worst air among the southern states: Hyderabad with 98 days of bad air (AQI of moderately polluted or worse) is the city with most unhealthy days in the southern states. It is closely followed by Andhra cities -- Visakhapatnam with 86 days, Rajamahendravaram with 68 days, and Amravati with 66 days of bad air. Smaller industrial towns of Karnataka namely Gadag and Kalaburagi also report significant bad air days; in fact, the AQI in these cities can cross into very poor category, but due to massive amount of missing data it is unclear how long these bad air episodes actually last. Gummidipoondi has the most bad air days in Tamil Nadu, and Kollam shows the same results in Kerela.
Bad air days begin to build up around the end of December in the cities of south Indian states and tend to increase till end of March. Hyderabad and cities in Andhra Pradesh show more pronounced impact of winter pollution compared to other cities of the region.
High weekly pollution episode during winter can be more than double the annual concentration in several cities: During the worst weekly pollution episode in winter, the PM2.5 concentration can increase significantly higher than the annual PM2.5 average – about two times higher in several cities. Worst episodes are noted in the industrial towns of Karnataka, where Gadag registered a shocking weekly average of 192 ug/m3 (almost five times its annual average). Similarly, Kalaburgi recorded a weekly average of 104 in mid-December.
Among non-industrial cities, during the high pollution episodes, weekly PM2.5 levels can go as high as 100 ug/m3 as recorded in Amravati in December 2021. This winter so far the highest weekly level was recorded as 95 ug/m3 in Hubbali, 89 ug/m3 in Visakhapatnam, 86 ug/m3 in Rajamahendravaram, and 81 ug/m3 in Hyderabad.
Changing ratio of PM2.5:PM10 during different seasons of 2021 – PM2.5 share increases during winter making air more toxic: The PM2.5/PM10 ratio is a useful indicator to understand the impact of coarse dust vs tinier dust from combustion sources on air quality. 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 average for two different seasons: monsoon (June-October) and winter (November-January).
The PM2.5/PM10 ratio in all the cities of the southern states has an increasing slope in winters, compared to monsoon -- except Thrissur and Kollam in Kerela, which are showing high percentage of PM2.5/PM10 ratio in monsoon compared to winter. Mostly, the concentration of PM2.5/PM10 ratio is higher during the winter months (November to January) hovering between 50 to 70 per cent. This is indicative and there can be variations across years. However, this trend is broadly consistent with what has been noted in other regions of the country.
In Andhra Pradesh, Tirupati is showing a high percentage of PM2.5/PM10 ratio -- 72 per cent in winters. It is followed by Chikkaballapur in Karnataka with 65 per cent and Kochi in Kerala with 62 per cent. Overall, in the southern India region, the concentration of PM2.5/PM10 ratio is higher during winters (November to January).
Multi-pollutant crisis during winters – along with particulate nitrogen oxide (NO2) -- increases during winter: There is a significant increase in the amount of nitrogen dioxide (NO2) in air of all cities of southern states during December compared to the previous months of November, October and September in most cities of south India. Coimbatore with 52 µg/m3 monthly NO2 average for December, is the highest in the region. It is followed by Kalaburagi (51 µg/m3), Kollam (40 µg/m3), and Visakhapatnam (38 µg/m3).
As for the seasonal increase in NO2 concentrations, smaller cities lead the list. Kalaburagi registered 5.8 times jump in monthly NO2 level; Thoothukudi registered a 4 times increase; Kozhikode had a 3.8 times rise, Hubballi was 3.3 times, and Thiruvananthapuram registered a 2.2 times increase.
Surface ozone increases during winter, making air more toxic: There is a significant increase in amount of surface ozone (O3) in the air in all cities during December, compared to the previous months of November, October and September. Rajamahendravaram with a 106 µg/m3 monthly O3 average for December is the highest in the region, which means ozone exceeded the standard in the city on almost every day of December. It is followed by Kalaburagi (93 µg/m3), Udipi (81 µg/m3), and Amravati (70 µg/m3). The problem is especially acute among smaller cities. It is also interesting to note that surface ozone has been relatively lower this winter compared to the previous winter for almost all the cities.
Pollution profile of individual cities
Hyderabad: Analysis of days as per AQI categorisation shows that Hyderabad city’s air quality is declining. Number of days recording AQI level worse than satisfactory has increased to 98 in 2021 from 60 days in 2020 and 86 in 2019. Sanathnagar has the worst air in the city, with its December average hitting 83 ug/m3. This is followed by Central University at 57 ug/m3 monthly average for December.
Bengaluru: Analysis of days as per AQI categorisation shows that Bengaluru has been able to hold on to most of air quality gains made during 2020. The number of days with the AQI worse than satisfactory (or meeting the standard) was nine in 2021; this is more than the three days in 2020 and much less than 22 days in 2019. Number of ‘good’ AQI days in 2021 stood at 208, which is just marginally lower from 214 good AQI days recorded in 2020. It is an improvement of over 30 per cent from 2019. Within the city, Bapuji Nagar was the worst hit with its December average recording 76 ug/m3. Pennya had the least polluted air with a 36 ug/m3 monthly average for December.
Chennai: Analysis of days as per AQI categorisation shows that the Chennai has been able to hold on to most of its air quality gains of 2020. Number of days when the AQI was worse than satisfactory was six in 2021, same as in 2020. But 2019 had witnessed 50 days. Within the city, Manali Village has the worst air with its December average adding up to 56 ug/m3, closely followed by Arumbakam with 54 ug/m3. Velachery has the least polluted air with 19 ug/m3 monthly average for December.
Kochi: Analysis of days as per AQI categorisation shows that Kochi city has not been able to sustain the air quality gains of 2020. Number of days when the AQI was worse than satisfactory was eight in 2021 -- up by four days compared to 2020. But 2019 had witnessed 50 days above the satisfactory category. Most significant reduction is noted among ‘good’ AQI days which are down by 43. Within the city, Vyttila has the worst air with its December average adding up to 56 ug/m3. Udyogamandal has the least polluted air with a 33 ug/m3 monthly average for December.
Visakhapatnam: Analysis of days as per AQI categorisation shows that Visakhapatnam has not been able to sustain the air quality gains of 2020. Number of days when the AQI was worse than satisfactory has risen to 86 in 2021, in contrast to 69 in 2020 and 73 in 2019. Though the number of days with very poor AQI has come down, but this overall increase in bad air days is alarming.
The next steps
Says the CSE analysis: “States in southern India have a unique locational advantage, with the sea and well-ventilated atmosphere and a more moderate climate that prevents pollution build-up during winter like it happens in north India. But this region is at the risk of losing the air quality gains of pandemic, though it has not yet reached the pre-pandemic levels. The doubling of pollution during winter also indicates high local pollution and exposure that normally is not well captured in the annual average trends. This indicates the need for urgent action across all sectors to control pollution from vehicles, industry, power plants, waste burning, construction, and solid fuel use in households in all the states to meet the clean air standards throughout the year.”
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