The level of sulphur-dioxide (SO2) in the air has reduced significantly after the closure of Sterlite’s plant at Thoothukudi, claimed the Tamil Nadu Pollution Control Board (TNPCB) to justify the State government’s arguments that SO2 was a major reason for high levels of pollution in the port city, and the decision to close the plant was correct.

The TNPCB on Sunday submitted a comparative study before the three-member panel of the National Green Tribunal (NGT) in response to industry’s claims that there was no appreciable change in the ambient air quality after the plant’s closure.

SO2 levels on September 22, 2017 (sample taken on top of FB substation 230 Kva-Sterlite switching station) was around 20 micrograms per cubic metre (MPCM). However, it was less 5 MPCM on October 12 and 13 (sample taken on top of scaffolding of All India Radio).

There has been an increase in the level of Particulate Matter (PM) to 64.9 MPCM on October 12 and 13 as against 56 MPCM on September 22, 2017. This could be due to the dust emanated from the open dump such as gypsum, slag and secured landfill facility.

Similarly, the level of nitrogen dioxide reduced to less than 5 MPCM in October as against 15 mpcm in September 2017, the TNPCB said in its submission to the panel headed by Justice Tarun Agrawal, former Chief Justice of Meghalaya High Court.

The panel was constituted after Sterlite’s parent company Vedanta petitioned the tribunal to consider reopening the plant that was sealed on May 28 due to protests by locals against alleged pollution.

On its part, counsels for Sterlite concluded their arguments. “The government’s reaction was only knee-jerk without any proper analysis and hence Sterlite had to face the unpleasant consequences,” said Sterlite sources.

MDMK leader Vaiko will again argue before the panel tomorrow, sources said.