Diesel cars are rapidly becoming the demons of the road, targeted with surcharges and scrappage schemes and blamed for air pollution that contributes to cancer, asthma, stroke and heart disease.
But are officials letting a bigger problem sail past them while they focus on drivers?
For years the shipping industry has gone largely unchecked when it comes to fuel emissions.
Yet analysts warn the maritime industry, that includes vessels such as cruise ships or shipping containers delivering our iPhones or consumer goods, use bottom of the barrel-style fuel and emit dangerous levels of sulphur oxides.
These are also contributing to air pollution and could be as much, if not more, of a factor in creating the chemicals in the atmosphere that medical experts warn can cause cancer, asthma and other issues.
There have been various studies in recent years pointing to the health dangers from sulphur and shipping.
In 2009, a study by the Danish government’s environmental agency found the chemicals in emissions from one container ship are equivalent to 50 million cars.
More recently in 2012, NABU, a German non-governmental organisation dedicated to conservation at home and abroad, found one 7500kg cruise ship emits as much sulphur dioxide as 376 million cars.
There are attempts to reduce shipping emissions, led by the United Nations’ International Maritime Organisation.
Ships must currently cap sulphur content in their emissions at 3.5 per cent, and this is being cut to 0.5 per cent after 2020.
Vessels sailing in emissions control areas - around the Baltic Sea area; the North Sea area; the United States coast, Canada coast, Puerto Rico and Virgin Islands – already have a lower 0.10 per cent cap on sulphur content.
Outside of this zone, ships will need to cap sulphur content to 3.5 per cent.
The trouble is, there is no single authority that polices international waters and no standardised detection methods.
There are also disparities about who enforces the rules as a ship has a flag state based on where it is registered, and a port state that reflects the jurisdiction it is entering.
Daniel Rieger, transport policy officer for NABU, warns that while cars can become more environmentally friendly by going electric, it is unlikely ships will ever have the capacity to store enough power, so more technological solutions may be needed.
He said: “Ships are using the dirtiest fuels on the market.
“While we have euro 6 standards for vehicles, this isn’t the case for the vessels.
“Ships don't have any exhaust gas aftertreatment systems installed even though stricter standards will come into effect by 2020.
“The requirement to install filters and catalysts like on land is not something that will happen in the next few years as there are so many lobby groups and countries involved.”
So, it’s all very well for the UK to ban new petrol and diesel car sales from 2040, or to have a toxicity charge in London, or surcharges on parking permits for dirtier vehicles in Edinburgh, but what impact will it have if the port you are parked in is even more polluting?
It’s like boasting about being a vegetarian while your neighbour holds a barbecue and hog roast next door. The pig is still going to die, even if you are not the one eating it.
But Rieger says everyone needs to play their part, both on land and sea.
He said: “Both need to be addressed at the same time as the air pollution problem is so massive, especially where both sources occur simultaneously like in port cities and close to the coast line but even in-land.
“Proper hardware solutions like particulate filters and nitrogen catalysts could have helped vehicle manufacturers avoid driving restrictions or complete bans for diesel cars that we are now seeing, but everyone has to address things that they can control.”