As winter sets in, the issue of air pollution once again takes centre stage, especially in cities like Delhi, where air quality worsens, affecting residents’ health. Though attention has traditionally focused on northern cities, recent studies have raised growing concerns about the air quality in southern cities like Chennai.
A recent study by the Lancet Planetary Health reveals troubling findings, showing that Chennai, despite having lower levels of air pollution compared to the cities in northern India, faces a significantly high mortality risk. The city, with an annual PM-2.5 (fine particulate matter) level of 33.7 micrograms per cubic meter, is estimated to have 2,870 deaths linked to air pollution each year.
Similarly, a 2023 Greenpeace report titled ‘Spare the Air 2.0’ analysed air pollution trends in 10 southern cities. It found that Chennai’s monthly average PM-2.5 levels were four to seven times higher, and its PM-10 (coarse particulate matter) levels were three to six times above the limits recommended by the World Health Organization’s annual guidelines.
Air quality standards differ
There’s a stark difference between national and international air quality standards. For example, the National Ambient Air Quality Standards (NAAQS) set the annual PM10 limit at 60 μg/m³, while the WHO recommends a limit of just 15 μg/m³. Similarly, the NAAQS standard for PM2.5 is 40 μg/m³, while the WHO suggests a limit of 5 μg/m³.
These findings show the urgent need for robust monitoring of air quality. However, simply collecting data is not enough. Citizens should be able to interpret this data and the government must communicate crucial information promptly, especially when the risk from air pollution is high.
Here’s a simple guide to the air quality monitoring systems in Chennai and how to read the data they provide.
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Understanding Chennai’s air quality monitoring system
Chennai has two main systems for monitoring air quality: manual monitoring stations and Continuous Ambient Air Quality Monitoring Stations (CAAQMS).
In manual monitoring stations, the device is placed in a spot for 24 hours (6 am to 6 am) and is operated by a human. Chennai has eight manual monitoring stations across the city as mentioned below:
- Kathivakkam
- Manali
- Thiruvottiyur
- Nungambakkam
- Anna Nagar
- T Nagar
- Adyar
- Kilpauk
According to a Tamil Nadu Pollution Control Board (TNPCB) official, as many as 104 samplings (two samples per week) are done every year. Four parameters — PM-2.5, PM-10, SO2 (Sulphur dioxide) and NO2 (Nitrogen dioxide) are measured using the manual sampling method. The operational cost of a manual monitoring station is around Rs 3 lakhs.
The results are notified to the Union government by December-end every year and both TNPCB and the Central Pollution Control Board (CPCB) publish a report.
The data from the manual monitoring stations can be accessed from the TNPCB web portal here.
Continuous monitoring
Additionally, CAAQMS gives the real-time values of the pollutants. Chennai has eight such CAAQMS that function 24×7 throughout the year.
- Kathivakkam
- Manali
- Royapuram
- Kodungaiyur
- Koyambedu
- Perungudi
- Velachery
- Alandur
In addition to PM-2.5, PM-10, SO2 and NO2, the CAAQMS also measures O3 (Ozone), CO (Carbon monoxide), NH3 (Ammonia) and NOx (Nitrogen Oxides).
The data from the CAAQMS can be accessed here.
“The data from the manual monitoring stations is valid in the court of law because of the methodology and analysis, while the data from CAAQMS gives a real-time reading but is not valid in a court of law,” adds the TNPCB official.
Similarly, the average values from the manual monitoring stations will only be considered to see if the city has exceeded the standard annual average value set by the CPCB, he adds.
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How is Air Quality Index (AQI) calculated?
The overall AQI is calculated only if data from at least three pollutants are available, with one being either PM-2.5 or PM-10. At least 16 hours of data are needed to calculate the AQI. Real-time AQI can be accessed through the TNPCB website, and manual stations use an AQI calculator for users to enter data and get the AQI value.
Based on the National Ambient Air Quality Standards (NAAQS) of AQI values, the possible health impacts are assessed. Pic Courtesy: CPCB
Health implications of key pollutants
“Of all the pollutants, particulate matter, particularly PM2.5, is the most harmful,” notes Prabhakaran Veeraarasu, an Environmental Engineer from Poovulagin Nanbargal. “These tiny particles can be inhaled, penetrate deep into the lungs, and even enter the bloodstream. Long-term exposure to PM2.5 can decrease life expectancy.” He adds that pollutants like SO2 and NO can cause eye irritation and other health issues.
A 2023 study by the Center for Study of Science, Technology and Policy (CSTEP) highlighted that in 2019, PM-2.5 emissions in Chennai were around 26,996 tonnes per year, with transportation contributing the most (53%). Other major sources include road dust (26%) and waste burning (7%).
Moreover, the study titled What Makes the Indian Megacity Chennai’s Air Unhealthy? – A Bottom-up Approach to Understand the Sources of Air identified over 100 pollution hotspots in Chennai including Manali, Kodungaiyur, Pudupet, Perungudi, Ayanavaram, Ambattur Industrial Estate, Sowkarpet and Aminjikarai. The study suggests that industries, road dust, transportation, and waste burning should be targeted for local pollution control measures.
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The need for effective communication from the government
The link between air quality and public health is undeniable. According to the Air Quality Life Index (AQLI) 2023 report, air pollution reduces the life expectancy of Delhi’s residents by an average of 11.9 years.
Despite this, there is a lack of clear communication from government bodies about air pollution levels. As Prabhakaran notes, while experts know where to find the data, the general public is often unaware of when pollution levels are dangerous or what steps to take.
When the AQI is satisfactory (50 to 100), the NAAQS says that sensitive people would have minor breathing discomfort. “On most days, Chennai’s air quality is satisfactory. However, how will residents, who are sensitive know that they will have minor breathing trouble if the government does not properly inform them?” asks Prabhakaran.
Given the serious health impacts of air pollution, the government must take responsibility for keeping the public informed.
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Need for expansion of air quality monitoring stations in Chennai
The number of air quality monitoring stations (CAAQMS) increased from three in 2019 to eight currently. However, Prabhakaran insists that Chennai needs at least 20 air quality monitoring stations.
While establishing that CAAQMS are expensive, the Indian Institute of Technology Madras (IIT-M) has developed low-cost mobile air pollution monitoring sensors that could serve as a cost-effective alternative. IITM’s ‘Kaatru’ project aims to provide hyperlocal air quality insights to empower individuals and communities to make informed decisions about their environment. These pollution sensors can be mounted on public vehicles and can dynamically monitor the air quality of an extended area at high spatial and temporal resolution. “The crowd-sourced data from the devices will then be stored in a cloud service and be available for public access in the Kaatru web portal. The pilot project in Chennai is ongoing in Koyambedu with five stationary devices and five mobile devices,” notes Professor Raghunathan Rengaswamy, Dean (Global Engagement) and Faculty, Department of Chemical Engineering, IIT Madras.
Expanding the monitoring network would allow for more detailed, hyperlocal data and help the government design more effective air quality management strategies.