Yes, it's been so easy to measure that it took years for anyone to realise what VW were doing... I'm afraid after VW none of these studies are really credible in any way.
People realised the basic problem for ages, they just thought it was due to the tests being unrepresentative of real-world driving - which they are, and is the correct explanation for most car manufacturers as far as we know. The studies are as valid as they ever were in terms of the effects they describe, which is that NOx from diesels in the real world is higher than the official test figures say.
Like diesels, petrols aren't nearly as 'clean' as anyone would like them to be,
No, but they're cleaner than diesel, and they're the most readily available alternative for cars. Heavy vehicles can keep using diesel with AdBlue and DPFs. Better to have a readily available "good enough" technology actually used on a big scale than a perfect one that's too expensive or otherwise problematic for widespread use.
not to mention being less efficient. They are just simply not an answer and the falling oil price scuppers it totally, no matter the propaganda.
How on earth does the falling oil price scupper anything? That will *help* the less fuel-efficient technologies, not hinder them, by reducing the cost of the inefficiency. Your statement doesn't follow.
The simple arithmetic is when you more throughly burn the fuel you get more emissions. That's the way the engine works
You're ignoring aftertreatment. It's OK to produce a pollutant if it's cleaned up before it gets into the atmosphere. Petrol catalytic converters are very efficient at removing NOx and have got ever better in recent years (diesel ones are not as the reduction reaction doesn't go in the oxygen-rich diesel exhaust). More "thoroughly burning" the fuel will, if anything, reduce emissions of hydrocarbons and carbon monoxide, as they're the products of incomplete combustion.
In any case, NOx is produced by high temperatures causing a reaction between the nitrogen and oxygen in the air. More "thorough" burning has nothing to do with it - crappy old carburetted cars produced plenty of NOx, despite having a large amount of incompletely burnt fuel in the exhaust.
and of course they're going to produce less than a diesel without a DPF, which is a downright bizarre thing to qualify that with. Remove the catalytic converter and filters and see what happens in reverse.
Not bizarre at all. DPFs don't block everything. Port-injected engines can produce less particulate matter than a diesel *with* a DPF, as can direct injection with appropriate design. It's just that that wasn't designed for until now because soot wasn't part of the petrol tests until recently (as old petrol engines produced so little of it).
In continental Europe where diesel is the same price or less expensive than petrol, which is what it should be as the fuel is cheaper to produce, the maths are quite easy to work out.
Indeed it is, and I was bored enough to do it once. The untaxed price of fuel at the moment (in the UK) is about 36p/litre vs 40p/litre for diesel (the tax is the same per litre, so the basic price of diesel is higher). For 10,000 miles a year that makes about £70 per year difference in fuel cost (diesel car getting 50mpg and petrol one about 25% less, which is typical. The difference is smaller for more modern petrols.). Nowhere near enough to justify the extra purchase cost. Even double that probably wouldn't be for most people. It's only the tax system that makes it so - why do you think diesels are far less popular outside Europe?
Hybrids are not only hellishly complex but they are incredibly expensive to maintain.
The Prius is one of the most reliable cars you can buy, so I don't know where this "incredibly expensive to maintain" comes from. Hellishly complicated? You're just replacing a starter, alternator, and complicated conventional transmission with two motor-generators, a NiMh or Li-ion battery and a simpler transmission (look it up, it's really quite elegant). More expensive, certainly, as the motors have to be much more powerful, but not really more complicated.
They're certainly more expensive than a diesel engine. Electric vehicles have far fewer moving parts and simply don't need the oils and lubricants a modern combustion engine does.
True, but the capital cost of the batteries is vastly greater than the cost of a few litres of lubricant oil every year. And all the non-engine parts will need maintenance just the same.
It's a question of where the future is if people really care about emissions and want something that is efficient whilst being cheap enough to buy
But they're not cheap enough to buy yet, that's the point. Maybe they will be one day, maybe not.
and especially maintain and there really isn't any more efficiency to be hammered out of the internal combustion engine. The best you can ever hope for in terms of efficiency for a combustion engine is 40% (being very optimistic) - and that's with a turbo, energy recovery systems and every piece of expensive technology you can throw at it. It really is over.
Diesel engines can already do better than 40% - and old diesels too, without all the complicated stuff. The pretty standard engine in the Prius can do high 30s. But again, why does a modest efficiency mean "it's over"? 25% is good enough if the fuel's cheap enough that the total cost of ownership is lower than the more efficient alternatives. And so far that's still the case - despite the huge taxes on fuel in Europe.
If it's complexity you're bothered about then I don't know how you can support the diesel engine. Modern diesels are hellishly complicated - turbochargers, DPFs, urea systems (in some cases), ultra high pressure injectors machined to insane tolerances. The old ones may have been simple, but not the ones you can buy today.
Once you start using heaters and air conditioning systems in a car the comparisons get even more unfavourable when it comes to petrols
That doesn't make sense, heaters use free waste heat (of which there's more with a petrol engine due to the lower thermal efficiency) and aircon is just an extra load on the engine, and will affect petrol and diesel similarly.