They produce a flame above 1,000oC, and so produce a miniscule amount of NO and NO2 (NOx). The main source of NOx is natural lightening. NOx is washed out of the air as very low concentration nitric and nitrous acids: Leaving a static level of 4 parts per billion NOx ion the air – 0.00000004%.
A static trace gas. Lightening produces a million times more than cars. So the worst we can say, is that both fertilise plant growth. Diesels release less CO2.
Photosynthesis sucks CO2 and SO2 out of the air. Leaving a pre-industrial 2 parts per million CO2 in the air: a static trace gas affects nothing. So burning Fossil Fuels has increased active life on Earth – no possible effect on the weather.
So all people writing papers on Global Warming or man-made Climate Change should have been sacked. But academic work on Global Warming stopped 2005 – 10 years after the natural global climate started COOLING.
So diesels don't pollute – they fertilise plants, to take in CO2, and build plant biomass. That's the thing, Global Warming was devised by physics and nuclear power – biologists tried to tell them not to be such arses, but they insisted.
So diesels don't pollute – they stimulate plants to take in CO2. Biodiesel sucks CO2 from the air – so is a carbon 0 fuel oil: hence OPEC hate it.
Which is why CO2 emissions FELL by 6% last year – remember the global average level of CO2 in the air is capped at 2ppm by global photosynthesis on land and sea. 4.5% the year before.
So average CO2 is at 1890 levels – after the little ice-age ended.
Above the Poles CO2 is at 4ppm. And the temperature down to -50oC. Global Warming – embarrassing nuclear paid fiction. CO2 spiked at 4ppm globally, in the little ice-age. Less photosynthesis – CO2 levels controlled by nature. Man can't influence it.
Scientists or reporters who have written papers on diesel engines polluting should never be employed again.