OK, I'll bite.
A few years ago, we were all encouraged to buy diesel because it's far more fuel efficient, and produces half the CO of petrol.
To make diesels produce less NOx, EGR was introduced to reduce combustion temperatures. Doing that meant more hydrocarbons in the exhaust. The solution to which was swirl flaps to improve combustion in the low-oxygen environment caused by EGR.
It's worth remembering that EGR and swirl flaps only operate at low revs. Above 2k they do nothing at all, provided they're working properly. Which often they aren't, and then you get worse emissions than if they didn't exist.
Now soot. The risks of particulate emissions are not new. In the 1980's the campaign group that opposed the construction of the M40 highlighted particulates as a challenged to the health of sensitive individuals living alongside the new route. The government dismissed the objections as minimal harm.
In 2012 the risk of particulates was reassessed by the WHO, who regraded them from 'probable carcinogen' to 'carcinogen'. The research behind this was solid: a 40 year US study of miners working underground with diesel plant. That found a small but definite risk of cancer from really rather intensive exposure to diesel exhaust, and especially the smallest particulates.
However, every vested interest lobby group has seized on this and you now daily see figures anywhere between 8,000 and 50,000 Londoners, allegedly dying prematurely from diesel vehicle use. These are estimates, guesses, nobody knows. There is no adequate research that says these numbers are actually true, and a sh*tload of lobbyists who often have tax or ideological motives for a War on Diesel (formerly the War on Petrol).
For perspective on probable risk before the green axegrinders added their tilt, this is well worth reading:
Diesel exhaust fumes 'definitely' cause cancer - should we be worried? - Cancer Research UK - Science blog
Now, we are told that diesel drivers are antisocial *******s and killers, when a few years before we were saving the planet. And as always, the only solution on offer is to punish with tax. London is now getting an ULEZ, which will raise costs to £25/day. Which actually means that provided you are wealthy or can claim the cost from your business, you can carry on polluting. How this is a solution GOK.
With classic joined up thinking, LHR expansion is going ahead. The M4/M25 LHR junction already has the worst air quality in London, except Oxford Street. Government is so concerned that it plans to add to road traffic there by 30% (plus aircraft pollution), whilst reduction will be achieved by ...FFS... extending the ULEZ to include LHR. Poor people can go to Luton.
This is all nuts and *********. Of course there is risk, every damn thing we do has consequences for someone. There is always a risk/benefit calculation.
Let's say diesel is bad and unacceptable. That's happening with taxis within the ULEZ. Operators will have to use zero emission EV taxis from (IIRC) 2020. The trouble is
(a)they will have to buy 2 EV taxis to replace each diesel one, because of the battery duty - so one can be on charge whilst the other is working. This is actually the plan.
(b)they will cost an awful lot of money, so fares will be much higher and only accessible to relatively rich people
(c)making new vehicles is environmentally costly and lifetime fuel consumption seldom exceeds the carbon cost of making the damn thing in the first place.
Where the War on Diesel is going is pretty obvious. They will be taxed off the roads ASAP and people will be induced to buy EV's. You know how this goes. Electricity for EV use will then be massively taxed because there is nothing like enough generating capacity to support mass EV use. We'll need 10 more Hinckley C's at a cost of hundred of £Bn, and no doubt more ridiculous price guarantees to France and China (Hinkley C guarantees 3x current wholesale prices for the next 30 years - if they can ever get EPR working).
Building new vehicles pollutes, nuclear pollutes, even manufacturing wind turbines and solar panels pollutes, and there will be a huge financial cost. None of which means that it shouldn't happen. I am rather a fan of EV's, but there is absolutely no free lunch to be had. The best that will happen is that EV's displace pollution from Oxford Street to China or Sellarfield or Germany, where someone else can get cancer instead.
So I don't feel like a murderer, having deleted swirl flaps and EGR rather than scrap the car (1.9 16v with the hand grenade metal flaps - see my avatar for details). My personal sense of responsibility - to say nothing of financial limitations - means I only ever use the car for longer journeys, use my legs or public transport in London, motorcycle when that makes more sense. I used to spend £4-5k/year on supplies for my business, using a car into London. Since CC came in, I no longer do that, ever. I buy over the internet and delivery services using diesel vans get to pollute instead. The best way of not polluting is to stay indoors and use no energy and not eat or use water. I shouldn't even be using the computer, someone somewhere will be suffering the consequences of making it and the electricity it consumes.
It would be more rational to have a War on Buying New Cars, or a War on Cars Made To Last 10 years. But nope, this is the Age of iPhone economics. What was state of the art risk calculation in 2011 is now hopeless and must be deprecated, now empty your wallet.