Ford is the latest car company to launch an incentive for UK consumers to trade in cars over seven years old, by offering £2,000 off some new models.
Unlike schemes by BMW and Mercedes, which are only for diesels, Ford will also accept petrol cars.
Ford said all of the part-exchanged vehicles will be scrapped, having an immediate effect on air quality.
Campaigners said it was a step in the right direction but the government had to do more.
'Part of a journey'
Speaking on the BBC's Today programme, Andy Barratt, chairman and managing director of Ford of Britain, said its scrappage scheme "is part of a journey" to improve air quality.
"We have some pretty large incentives here, up to £7,000 if you have a commercial transit vehicle," he said.
"We're the only scheme open to commercials. It is part of a journey.
"Air quality is a much bigger debate and getting older vehicles off the road is part of that.
"New technology, such as plug-in hybrids etc, are all part of that longer journey we need to work together."
He denied it was simply a ploy to sell more cars.
Consumers will be given £2,000 off new Ford models ranging in price from about £12,000 to more than £20,000.
Ford said that by combining the scrappage incentive with other standard offers, customers could receive up to £4,000 off a car or £7,000 off the cost of a van.
Under Ford's scheme old cars, from any manufacturer, can be exchanged until the end of December.
The cars that can be traded in include any built to emissions standards that applied before 2010.
Vauxhall ran a similar scrappage scheme earlier this year, as well as in 2015 and 2016.
James Baggott, editor-in-chief of Car Dealer magazine, speaking on "Wake Up to Money" on BBC Radio 5 Live, said the scheme was good for Ford, for consumers and the environment because it meant the worst polluting cars were being removed from roads.
"It means people can swap one of these old, dirty diesels, which is going to be worth less than the £2,000 that they (Ford) are giving them in part exchange for it.
"They can buy a new Fiesta for I think around £10,700. That's actually a good deal," he added.
Mr Baggott said new diesel engines were "extremely clean" compared with their older counterparts, so even just upgrading a diesel vehicle would help towards better air quality.
But he said this was a transitional phase: "We need to look to the future, to electric cars, hybrid cars, fuel cell cars. They are what we need to be looking towards.
"I would like to see schemes like this incentivising customers to buy cleaner electric vehicles."
Peter Campbell, motor industry correspondent for the Financial Times, said greener options were still limited.
"Almost no-one on the market right now has an affordable electric car that can drive a decent range using its batteries before needing recharging.
"These cars are coming and will come in the next five years and all the carmakers have to meet these emission targets that are coming into force in 2021.
"What many people will do is use this to buy smaller cars, and to be fair to Ford, the new cars they're selling - the new diesels, the new petrol - are orders of magnitude cleaner than the ones bought in 2009."
The government's clean air strategy announced in July did not include a scrappage scheme, although it proposed a consultation on it later in the year.
Instead, it said new diesel and petrol cars would be banned from 2040.
It made the announcement after losing a case against environmental law campaigners Client Earth over breaches in EU emissions standards.
Client Earth lawyer Anna Heslop welcomed Ford's scheme but said it could not make up for lack of action by the government.
"It seems the motor industry is finally waking up to the damage dirty diesels are doing to our lungs as well as their own reputation.
"What we need is a thought-through, coherent strategy from government to help people to move to cleaner and more sustainable technology.
"At the moment, there are pockets of small, short-term actions here and there, but nothing like the joined-up thinking we need to solve this problem," she added.
Steve Gooding, director of the RAC Foundation, agreed there needed to be an overall strategy.
"The problem with a scrappage scheme aimed at air quality, is that it really needs to be targeted at the vehicles that are driving around the most, in areas where air quality is a problem," he said.
"Things like buses and trucks are particularly important and so are commercial vehicles too."
Analysis: Richard Westcott, BBC transport correspondent
No-one could accuse the car industry of rushing to solve air pollution.
Manufacturers have long been accused of dragging their heels over plans to tighten the legal emissions test.
And for years, they happily sold cars that they knew were far more polluting on real roads than in the official lab test.
But companies are now taking the initiative with old car scrappage schemes.
Ford is the latest to offer a plan, and their version insists that the older, polluting car is destroyed rather than resold.
But the offer is only open until the end of December.
And let's be frank, it is also an attempt to boost sales which have been flagging across the industry for the past four months.
It's hard to see it making a big dent in the dirty air problem.
Ford, BMW, Vauxhall and Mercedes sell around one million cars in the UK.
The scrappage schemes will help support sales at a time when demand for new cars is beginning to show signs of a sustained drop for the first time in around six years.
In July, new car registrations fell for the fourth consecutive month in a row, hit by a number of factors including uncertainty over Brexit, and lack of clarity over future government plans around new levies on diesel models.
The UK's last government-backed scrappage scheme came in the wake of the financial crisis and ran for nearly a year from mid-2009, helping to support the car sector which had been hit by nose-diving sales.