London's air pollution problems rose up the mayoral campaign agenda on Tuesday at the launch of Brian Paddick's manifesto.

The Liberal Democrat candidate's proposals include pledges to switch all the capital's buses and taxis to electric power by 2020 and the creation of a clean air zone in central London.

Simon Birkett, founder of Campaign for Clean Air in London (CCAL) praised the manifesto. "I think its tremendous that the Lib Dems have confirmed the 'big switch' [towards electric public transport] and put a date on it. It's great to see things which have been championed by the Lib Dems over the past three or four years in Brian's manifesto," he said.

He added that the current mayor, Boris Johnson, was becoming increasingly isolated from his fellow candidates when it came to pollution. "This election is rapidly shaping up into contest between Boris with his backward steps on air pollution and those like Brian and the Liberal Democrats who would act to address the biggest public health crisis for decades."

Last month, pollution in London hit record levels due to a mix of weather conditions and traffic fumes, in particular from diesel cars, vans and lorries.

Johnson is facing mounting criticism from campaign groups and fellow election candidates over his use of dust suppressant vehicles to improve London's air quality, which is currently among the worst in Europe. The trucks spray adhesive to the road surface, effectively glueing pollution to the ground.

Green party candidate Jenny Jones denounced Johnson's use of dust suppressants as a "quick fix" before the Olympics. "I think it's a cheat," she told the Guardian. "It's absolutely typical of this mayor, it's a complete cheat because what he's actually doing is lowering the amount of pollution that's being measured, he's not dealing with the pollution itself," she said.

Johnson's manifesto promises to establish a London roads taskforce that will look at ways to reduce congestion black spots and cut pollution levels in the city. He also wants to expand the cycle hire scheme to areas beyond central London.

Former mayor Ken Livingstone has accused Johnson of failing to tackle air pollution. "It is a scandal that inaction on air pollution in London means Londoners risk losing years off their lives. Urgent action must be taken to get London on the front foot in the fight to improve air quality," he said.

Birkett attributes the rise of air pollution up the political agenda to a better understanding of the harmful affect poor air can have on public health. Over 4,000 Londoners die an early death every year from air pollution.