Chennai
Even as Tamil Nadu Pollution Control Board (TNPCB) is looking to commission 25 new continuous air quality monitoring stations across the state, scientists say that sound and air monitoring must be complemented by source apportionment and good forecasting to prevent a Delhi-like situation. The sudden spike in pollution levels in the first week of November in Chennai and other parts of the State has set off concerns.
The Central and State Pollution Control Boards measure air quality by an Air Quality Index (AQI) arrived at on the basis of concentration of particulate matter, carbon monoxide, ozone, Nitrous Oxide, lead and sulphur dioxide in the air. On November 8, Central Pollution Control Board (CPCB)’s monitoring stations showed AQI levels of 347 at Manali industrial area, 287 at Alandur bus depot and 324 at Velachery (residential and traffic), well over permitted limits. Particulate Matter (PM2.5) was the major pollutant. The concentration of PM should not exceed 60 over a 24-hour period, says National Ambient Air Quality Standards (NAAQS).
PM2.5 (dust particles with a diameter of 2.5 microns or less and smaller than human hair) is considered a deadly air pollutant because it can enter the bloodstream, causing health problems. “Exposure to moderate or poor air, even for few days is dangerous for elderly, young and unborn children and precaution must be taken. For others, since the threshold limit of each body is different, it is difficult to assess long term health impacts.” Says Rajiv Khurana, Founder- Trustee, Lung Care Foundation.
The recent episode
While media reports suggested a strong link between the intense smog in Delhi around Diwali (and still persisting) and the haze in Chennai and other places in TN, scientists debunk that theory. “There is a 10 to 15 per cent increase in aerosols (suspended dust particles in the atmosphere) concentration in TN over the last few years due to overall growth and industrialisation. But what happened in November was the result of a unique combination of factors – meteorological and man-made,” says Vinoj Velu, Assistant Professor at the School of Earth, Ocean and Climate Sciences, IIT, Bhubaneswar.
In winters, the layer in the atmosphere where dust particles mix (mixing layer) stays low. Additional emissions at this time increase concentration of pollutants in the air. The southern peninsula receives a strong sea breeze, cleansing the air. This keeps pollution lower than northern cities.
This year, there was a late withdrawal of the South West monsoon, slower North-East monsoon and a resultant calm period where there was less wind than usual. Simultaneously, the cyclonic system in the Bay of Bengal took away air from the system, causing pollutants to stay in the air longer, says Dr Gufran Beig, Programme Director of System of Air Quality and Weather Forecasting and Research (SAFAR-Indian Institute of Tropical Meteorology).
“Dispersion models and data from satellites show the smog drifting between North India and East Coast due to meteorological phenomenon. The spike in Chennai's air pollution is due to a combination of fires and pollutant sources like thermal power plants that caused smog in Delhi and also local pollution sources like thermal power plants and vehicles,” says Raj Bhagat Palanichamy, an Earth Observation Expert working with World Resources Institute, India.
Officials of the TN Pollution Control Board say the CPCB monitors were not showing accurate numbers at that time and needed to be recalibrated. Numbers of the monitoring station at the US Consulate in Chennai showed that during the period, air quality was indeed unhealthy, but was by no means as high as was indicated by the CPCB monitors. TNPCB data indicates that air quality in the city was moderate in many areas throughout the year but excessive PM10 pollutants (diameter of 10 microns or less, which can get into the nasal passage) were found in T Nagar and Nungambakkam in January and June.
A report “Unfit to Breathe” by Health Energy Initiative-India and Coastal Resource Centre, said PM levels are higher than permissible limits in 15 locations in Chennai between May and July. “The device used to collect air samples was calibrated according to US Environmental Protection Agency standards. PM2.5 levels were higher than permissible in T Nagar and Velachery, “says Dr Vishvaja Sambath, Environmental Health Researcher, Health Energy Initiative.
“WHO guidelines state that concentration of PM should be less than 10 micrograms/m3. The national standard is 40 microgram/m3. It is virtually impossible to reduce level of developmental activity, but it is possible to monitor how much is emitted and how much is coming from outside. We need better forecasting of air pollution based on meteorological conditions,” says Velu, who is also the Orissa co-ordinator for the National Clean Air Campaign.
In January, the National Clean Air Programme (NCAP) was launched, which aims to bring down the PM2.5 and PM10 levels by 20-30 per cent by 2024 taking 2017 as the base year. 102 cities have been identified for this programme, including Thoothukudi for non attainment or exceeding permissible limits.
Dr Sachin S Gunthe, Associate Professor at the Department of Civil Engineering (IIT, Madras) and TN coordinator of the NCAP, cautions against relying completely on numbers without careful analysis. “It is possible that the numbers are within range, but the combination of pollutants more dangerous than when the numbers are actually looking bad,” he says.
The Central and State Pollution Control Boards are more of regulators who can identify higher levels of pollution. Any policy level changes must be taken by the government.
Particulate Matter
Know Your Pollutants
Major air pollutants are Particulate Matter (PM2.5, PM10) , Nitrous Oxide (N2O), Sulphur Dioxide(SO2), Carbon Monoxide(CO) and Ozone(O3)
Nitrous Oxide
N2O’s major source is combustion and chronic exposure causes lung disease
Standard: 24-hour average should be 80
Sulphur Dioxide (SO2)
SO2 affects mucous membranes of the nose and upper respiratory tract
Standard: 24-hour average should be 80
Ozone (O3)
Ozone can aggravate bronchitis, heart disease, emphysema, asthma and reduce lung capacity
Standard: 8-hour average should be 100
What is AQI?
Air Quality Index (AQI) transforms weighted values of individual air pollutant parameters (e.g. SO2, CO, PM2.5, PM10 etc..) into a single number. The major pollutant determines the overall AQI level
- News Research Department
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