Post the closure of the Sterlite Copper Plant in Tamil Nadu’s Thoothukudi city, the quality of air remains the same as it was before the industrial unit was ordered shut.

According to a Right to Information (RTI) response given by the Tamil Nadu Pollution Control Board (TNPCB) to Thoothukudi resident M Maheswarakumar and Tirunelveli resident U Kethrapal, there is no significant change in the ambient air quality per data collected by TNPCB in three locations of the city in the last 18 months after the unit’s closure.

One of the main charges made by TNPCB against the Sterlite copper plant was that it was the largest emitter of sulphur dioxide (SO2), thus causing air pollution.

But TNPCB data (available with Swarajya) provided in the RTI show that while SO2 concentration in ambient air was 12.63 µg/m3 (microgram per cubic metre) in April 2018, it was 13 µg/m3 in June this year and 11 µg/m3 in July.

It was recorded at 14.09 hours on 9 April this year. According to the National Ambient Air Quality (NAAQM) Standards, the permissible level is 50 µg/m3 annually.

The SO2 levels in Thoothukudi are also lower than the 80 µg/m3 over a 24-hour period.

(The annual measurement is a mean of 104 measurements taken at a particular site twice a week for 24 hours at uniform intervals. Values for 24 hours are monitored every hour or eight hours. The permissible levels can exceed but not on two consecutive days of monitoring.)

Sterlite contends that its copper plant has SO2 mitigation measures and thus its contribution to the chemical's concentration, per se, may not be more than one to two per cent. The TNPCB data prove its contention.

The company also points to the data recording the concentration of SO2 and other chemicals such as nitrogen oxides being well within permissible levels in Thoothukudi between 2003 and 2019.

Thus it argues that it has never been responsible for any pollution in the region.

The TNPCB data show that the presence of nitrogen oxides, especially nitrogen dioxide, was 8.63 µg/m3 on 29 April last year. It was 9.6 µg/m3 on 30 April this year.

The permissible levels as per NAAQM standards are 40 µg/m3 on an annual basis and 80 µg/m3 over a 24-hour period.

The presence of PM10 (particulate matter of 10 mm diameter and less) in Thoothukudi was 83 µg/m3 in April last year. By April this year, it was 85 µg/m3.

The permissible level for PM10 is 60 µg/m3 annually and 100 over a 24-hour period.

The presence of PM2.5 (particulate matter of 2.5 mm diameter and less) in the industrial city was recorded at 25.76 µg/m3 in October last year against 26.36 in April. In July last year, it had increased to 34.65 µg/m3.

The permissible level for PM2.5 is 40 µg/m3 annually and 60 µg/m3 for the 24-hour period.

According to the Australian Department of Environment and Energy, particulate matter, especially chemicals, of these size ranges make up a large proportion of dust that can be drawn deep into the lungs, thus affecting humans.

Larger particles tend to be trapped in the nose, mouth or throat.

The Thoothukudi Sterlite plant was ordered shut by the Tamil Nadu government after violence erupted during protests demanding the closure of the unit, leading to the death of 13 persons in police firing.

For nearly 100 days from February 2018, protests were held in Thoothukudi demanding that the copper plant, owned by UK-based Vedanta Resources, be closed, alleging that it was causing pollution to the industrial city of Thoothukudi.

Even before the plant was ordered shut, the Tamil Nadu Pollution Control Board withdrew its consent for the operation of the copper plant on charges that the Sterlite plant had caused air and water pollution.

Vedanta appealed against the closure before the National Green Tribunal (NGT), which quashed the state government and TNPCB orders terming the closure as against the principles of natural justice.

This was because the copper plant management was never given an opportunity to explain the charges that they were causing air or water pollution.

However, the Supreme Court overruled the tribunal’s verdict setting aside the state government’s closure order. It, however, gave Vedanta the liberty to approach the Madras High Court against the closure.

The case is now pending in the Madras High Court, where Sterlite’s plea is being heard, while the Central Bureau of Investigation (CBI) is probing the 22 May 2018 incidents that resulted in police firing.

The closure of the Sterlite plant has resulted in India becoming a net importer of copper. Until its closure, Sterlite contributed to 40 per cent of the total 1,000 kilotonnes of refined copper production in the country.