Pollution
Some of the observed figures in the city exceeded permissible limits when it comes to PM10, irrespective of commercial/traffic area or residential area.
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The air quality index of the state was released by Tamil Pollution Control Board (TPCB) on Tuesday. During the months of January to March this year, the air quality index (AQI) in Chennai mostly alternated between moderate and satisfactory with very rare good days only in residential areas.

Some of the observed figures in the city exceeded permissible limits when it came to PM10, irrespective of commercial/traffic area or residential area.

For instance, between February 27 and 28 this year, PM10 levels in Anna Nagar (residential) were at 153 microgram/cubic metre, while in Nungambakkam Valluvar Kottam signal (traffic area), the levels were at 189 microgram/cubic metre, beyond the 100 microgram/cubic metre permissible limit. PM2.5 observed at Anna Nagar was 57 microgram/cubic metre, edging close to the permissible limit. On March 12, Nungambakkam Valluvar Kottam signal recorded 231 microgram/cubic metre of PM10, over twice the permissable limit.

As per National Ambient Air Quality Standards, the permissible limits for PM10, particulate matter of less than 10 micron size, is 100 microgram/cubic metre. For PM2.5 the limit is 60 microgram/cubic metre and 80 microgram/cubic metre for SO2 and NO2 gases.

Satisfactory days are when air quality levels are between 51 and 100 micrograms/cubic metre and moderate days are those with levels between 101 and 200 micrograms/cubic metre. The rare good days are when AQI records less than 50.

While PM2.5 should ideally be below 40, both Anna Nagar and T Nagar recorded 49 and 44 respectively between February 21 and 22 2019.

Shweta Narayan, coordinator of Healthy Energy Initiative India, had told the Times of India that toxins such as PM 2.5 had significant effects on health. "We need to have more data sets. Only 24-hour monitoring of air will be able to provide data to draw any conclusion about pollution levels in the city,” she said.

However, the increasing levels of pollution in the city, even in residential areas, is an undeniable fact.

TPCB is operating eight ambient air quality monitoring stations in Chennai under National Air Quality Monitoring Programme (NAMP) funded by Central Pollution Control Board at Kathivakkam, Manali, Thiruvottiyur, Kilpauk, T Nagar, Nungambakkam, Anna Nagar and Adyar. These areas have been classified under industrial, commercial and residential and function on a 24-hour basis, twice a week.

Notably, TPCB did not have a station in Ennore in North Chennai, where fly ash was a recurring problem.

The samples collected from these stations are analysed for the Respirable Suspended Particulate Matter (RSPM) and gaseous pollutants such as Sulphur Dioxide (SO2) and Nitrogen Dioxide (NO2). RSPM is particulate matter less than 10 microns.