Controlling diesel fumes has helped improve the air quality in California’s Bay area — an example Calcutta can emulate, emission experts suggested on Thursday.

Two officials from California Bay Area Air Quality Management District shared their success over Skype with an audience at American Center in Calcutta. The officials narrated how they had come down heavily on diesel emission in the west American city.

“The Bay area was among the worst in the US in terms of air pollution. But we have improved significantly,” said Jack Broadbent, the air pollution control officer of the district.

Environmentalists working on air quality in Calcutta said the city should follow the California model and set a time frame for fuel switch. Almost the entire public transport fleet on the city roads run on diesel.

The Bay Area Air Quality Management District website mentions the various measures taken to improve air quality. “1995 brought the worst air quality in a decade,” the website says.

In 1996, the Air District started the Vehicle Buy Back Program, giving residents the opportunity to voluntarily give away their older, polluting vehicles in exchange for a monetary incentive. In the California Bay district, particulate matters from diesel exhaust were estimated to account for up to 70 per cent of the cancer risk from toxic air pollution throughout the Bay area.

“We introduced a lot of regulations on diesel-run vehicles. Even ships were asked to keep boilers switched off while entering the California Bay area,” Broadbent said.

In Calcutta, almost all buses and trucks and even a good number of private cars run on diesel. Autorickshaws that run on liquefied petroleum gas (LPG) and a handful of electric buses are the only public transport using alternative fuel.

“Vehicle emission contributes to 50 to 70 per cent of the air pollution in an urban area. In Calcutta, 98 per cent of public transport runs on diesel,” said activist Subhas Datta. The engines of most buses are BS-III stage-compliant, “less efficient than BS-IV engines and emit more pollutants into the air”.

Anupam Deb Sarkar, who teaches civil engineering at Jadavpur University, said diesel fumes also carry oxides of nitrogen that can trigger respiratory diseases.