Almost as regular as clockwork, the smell creeps up around 11.30 pm, say residents. It is so bad that ``it becomes difficult to breathe'', says Avinash Kolhatkar, a resident of the area. People in every house in the stretch between the Harinagar water tank and Ellora Park have the same complaint, according to another local resident.

Trupti Nene, businesswoman and resident of Upkar Society, describes the smell as ``pungent'' and says it occurs only after dusk. Adds Sudha Ojha, a home-maker, ``On getting the smell one day, I thought it came from the toilet. Then I realised that it came from outside. If one keeps the doors and windows closed, there isn't that much of a problem.''

But because of the season, that isn't possible. Last week, the smell finally drove a cross-section of local residents to write to the GPCB, demanding action. Nothing has happened so far.

According to GPCB regional officer N L Kansagara, that was because visits to the area did not yield any evidence of gas leaks. ``A resident told the team that a scrap-owner had been burning material near the ST colony'', he says, adding that the matter could be referred to the sub-divisional magistrate, who can act against guilty units in such cases.

While Kansagara maintains the GPCB's responsibility is restricted to checking on industries, Municipal Commissioner G R Aloria insists the entire gamut of air pollution is the GPCB's concern.

However, the civic chief admits that there is nothing to stop the Vadodara Municipal Corporation from taking action in the ``public nuisance'' case if it is brought to its notice. As a case in point, he claims the VMC recently sealed mini-refineries in Mandvi on the basis of complaints.

On his part, District Collector Anil Mukim says the SDM has the authority to slap a notice on polluters on the basis of complaints and that the civic body, too, could be asked to initiate action.

While Kansagara appears to subscribe to the kabadiwala theory of pollution, management consultant J C Shukla believes the gas could be released by Sarabhai Chemicals in the early hours of the day. He says he even led a delegation a year ago in asking the unit to cease polluting the atmosphere.

Kansagara, however, dismissed the contention that Sarabhai Chemicals could be the guilty party. Senior vice-president (production) of the company S V Talavliker, too, claims they have no plant that could be responsible for the foul smells.