Jamesp, yes! Google Mercedes elk test

SandyS, I would be very happy to buy a cheap VW Diesel. Co-incidentally, my petrol VW has had slight problems with electronic sensors etc, causing it to burn more petrol. It has cost me money to fix a problem, to save money, created by legislation, to save a perfectly healthy polar bear. The Garage recommended a good burn up on the motorway before the MOT...... also known as an Italian Tune-Up.

Stewgreen, if only all Green claims were as reliable as Volkswagen's

michael hart, agreed, what is NOx anyway? Is it just another noxious abbreviation?
Emergency generators are to be found in Government Departments and hospitals. Where would more NOx damage be noticed?

Get ready for new TV commercials, from solicitors wanting to earn fees from claiming compensation, for losses you never knew about. The millions involved, will be included as part of the toxic Green economy success story.

michael hart, chemists, anyone?

What produces NOx?

Would you get more, less or none, burning chip fat in your diesel car? Or Green bus?

A starting point for info on emission control technology:

http://www.meca.org/technology

GolfCharlie, the short answer is that NOx just means "Oxides of Nitrogen".

Their chemistry is generally complex. Depending on conditions in your body/atmosphere/car engine, you might start with one, and end up with many others and their reaction products. So it is often easier to lump them all together as a group. For the most part, when considering genuine pollution, I have no problems with this approach.

Martin A, essentially, yes.

Even more than many things in the climate system, Nitrogen (N2) chemistry is very far from equilibrium. The slowness to ever approach equilibrium in chemical reaction with Oxygen, or anything else, is actually the stand-out feature of N2 chemistry. So far from equilibrium, and so slow, that the concept of equilibrium is often essentially useless or misleading.

Petrol/diesel engines briefly change the rate and direction of reactions involving Nitrogen. The result is generally not a good thing for humans (unless you are blowing your drag-racing engine with nitrous oxide, N2O).

NOx thanks gentlemen. I have fixed a fair few yacht diesel engines, and have a reasonable understanding of diesels, but not electronic chip controls on cars, or emissions except from the blast of visible black smoke out of the blunty end, normally associated with slamming it into full astern just before the crash in a harbour/marina. The noise, plus black smoke normally gives a few seconds for everyone else to watch what happens next.....

If NOx can be produced by high temperature chip fat, are people who work in chippies at risk? Or American burger restaurants? Should we all have NOx meters in our kitchens before a fry up?

I heard a solicitor on BBC Radio 2 salivating over compensation claims for NOx. CO2 seems pretty harmless to animal life in 10x atmospheric concentrations, and plants love it. As a former scuba diver, instructor etc I have experienced nitrogen narcosis, but never the bends or burst lung. Is NOx now going to be found to be more toxic than cyanide, for the financial benefit of lawyers?

Until last week, who had suffered a financial or medical loss over VW? The potential consequential "losses" are limitless in the eyes of compensation lawyers.

GC, as with most substances deemed harmful or toxic, the devil is in the dosage.

More complexity, if you are interested:
It was only as recently as 1998 that The Nobel Prize in Physiology or Medicine was, rightfully, awarded to researchers in the US for their discoveries that Nitric Oxide (NO) is not only produced in the human body, but that it is indispensable for many important cellular biochemical signalling events. Nitric oxide was proclaimed “Molecule of the Year” in 1992. Given what was thought to be known about NO chemistry and toxicity at the time, much of this was stunning to medicine. The long used, but poorly understood, drugs of nitroglycerine and amyl nitrite are precursors to the formation of NO. Viagra also works by stimulating nitric oxide pathways.

Other dietary nitrites may have significant functions. You also have symbiotic bacteria in your salivary glands which, possibly uniquely in the human body, convert less reactive nitrates in your diet to the more reactive nitrites, and thus a source of NO which may possibly be in limited supply when needed in the digestive tract. As recently as ~2009 I was still trying to get to grips with some of this biochemistry in cardiology. Complex stuff, nitrogen oxide chemistry.

michael hart, thank you. I am interested. Chemistry was not a favourite subject at school, but the 'O' level knowledge/understanding gained, has been been very useful since.

The concept of NOx, was just too conveniently close to 'noxious', yet made no sense chemically. The way CO2 is portrayed, it should have the right to sue for malicious defamation. I have lost all faith in official GreenBlob health warnings about anything.

If invented today, the 'Snap, Crackle and Pop' of Rice Krispies would probably require a Health and Safety risk assement to make, and that is before you add milk and sugar, and try to ingest it.

Lightning plays a minor part in the fixation of atmospheric nitrogen. The extreme heat of a lightning flash causes nitrogen to combine with oxygen of the air to form nitrogen oxides. The oxides combine with moisture in the air. The fixed nitrogen is carried by rain to the earth, where, in the form of nitrates, it is used by plants. most areas probably receive no more than 20 lb nitrogen/acre per year from this source. . What, if anything, is the difference between lightening and diesel engines with regard to fertilising the soil?

France probably has as much of a problem from wood burning as diesel cars. I may be wrong but wood fires are permissible in Paris, no clean Air Act. and on still winter days here in rural Limousin there is a haze of wood smoke around all groups of dwellings. We live close to the main route from Portugal to Germany with thousands of lorries per week passing through. I have never noticed the smell of diesel fumes being stronger than wood smoke at those times.

Hi folks

When this VW story came up on an economics blog I frequent, I came over here to find the facts on NOx emissions, because this is a blog with a focus on empirical data. The fact that this discussion so far is based on anecdotes is surprising, so I thought I would try to track down some emissions data. It was surprisingly difficult.

Here is a graph for the UK:

http://akhaart.blogspot.co.uk/2015/09/the-vw-debacle.html

and here is the Pacific Southwest of the USA, which includes the heavily polluted Los Angeles mega-city:

http://www.epa.gov/region9/air/trends/no2.html

and here is the USA

http://www3.epa.gov/airtrends/nitrogen.html

All these graphs show steep declines in NOx emissions, despite the trickery of VW. It could be that consumer diesel engines account for a very small part of the total NOx emissions. Perhaps it might be worthwhile trying to find any French data, since diesel cars have been predominant there for many years. Given that France also burns much less coal than either the UK or USA, it could well be that emissions of NOx show a less pronounced downward trend.

I have heard it said that particulates in diesel exhaust are a far greater health hazard. However, in the last 10 or so years, the filtering of particulates has improved beyond measure, in consumer vehicles at least. I have no idea whether it applies to buses and trucks.

However, this fuss appears to be about NOx. And the trends appear to be declining fast, at least in USA and UK.

To build on Martin A's excellent explanations of the chemistry involved:

The higher the temperature, the more the balance of the chemical equation:

xN2 + yO2 <-> zNO + wNO2

tends toward the right hand side, producing the nitrogen oxides NO (nitric oxide) and NO2 (nitrogen dioxide), collectively NOx. (Note the nitrous oxide, N2O, is not a concern here.) At ambient temperatures, the balance is virtually entirely to the left hand side.

Any time you have combustion, you have temperatures high enough to produce significant NOx. If the gases can cool gradually, virtually all of the NOx will convert back to N2 and O2 as it cools. However, if it cools suddenly, as in the expanding piston of an internal combustion engine, this won't be the case. This is because the reaction to convert back requires a high-energy intermediate state to break the bonds, and this energy level is far less likely to be reached at ambient temperatures. So instead of a typical time to convert back of seconds, it can be days, leading to what we call "pollution".

This phenomenon is one of the chief problems with internal combustion engines, although I would wager that not one in a thousand of those calling IC engines "evil" understands this.

Diesel engines, with their higher compression ratios than Otto (a.k.a. petrol, gasoline, spark) engines, leading to higher combustion temperatures, have an inherently worse NOx problem than Otto engines. But of course, their higher temperatures also give higher thermodynamic efficiency and mileage.

Incidentally, the USA's stricter NOx standards than Europe's mean that US Otto engines run at lower compression ratios and get reduced mileage (~10% lower from what I can tell) compared to their European equivalents.

Enough for now -- hope to post more soon.

' I think it is the high compression ratio of diesels that results in their
greater efficiency (energy out, relative to fuel consumed) relative to petrol
engines.'

I thought the main difference was that diesel had about 10+ % more energy in it than petrol? or is it more efficient at burning it too on top of that?

http://www.diffen.com/difference/Diesel_vs_Petrol

Thank you to everyone on this thread. A rational exchange of views on the relative merits of diesel.

Diogenes, yes I agree about 'particulates' and their perceived threat. But rather like 'NOx', we are all guilty of using the term, without knowing the source of the perceived threat. Certainly wearing a cheap dust mask will show staining in use, and is a good propaganda tool.

If NOx levels are declining, where else is/was the NOx coming from?

A hot diesel engine works more efficiently than a cool one. Hence, I believe why diesel cars in the 80's/90's had a bit of cooking foil over the radiator grille. Electronic chip control allows an engine better control over its temperature than a simple thermostat on coolant flow, and engine fan. Is this correct or urban myth?

Interested to know more, from so many different viewpoints!

DEFRA offer the following explanations of trends since 1970:

Increases in road traffic account for the steep climb in nitrogen oxide (NOx) emissions between 1984 and 1989, and road transport still accounts for just under one third of total NOx emissions. Catalytic converters and stricter emission regulations have resulted in a strong downward trend since 1990. Emissions from
power stations have also reduced significantly. The recent decrease in NOx emissions between 2012 and 2013 was due to similar reasons to those detailed for SO2.

The recent decrease in SO2 emissions between 2012 and 2013 was due to a reduction in the market price of natural gas leading to less coal being used for power generation. Also, some coal-powered Power Stations reached the end of their working lifetime and were decommissioned, reducing the overall coalburning capacity.

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/388195/Emissions_of_air_pollutants_statistical_release_2014.pdf

I strongly suspect that consumer diesel engines are not responsible for very much NOx. Tractors and other commercial vehicles are probably greater emitters, as are coal-fired power stations, which is why I would be interested in any graphs of French data, given that diesel engine penetration there is high and there are few coal-burning power stations.

Diogenes, interesting stuff from DEFRA.

Do they still attribute the rise in global average temperatures to CO2, despite no rise in recent temperatures, to match the continuing rise in CO2?

My trust in Government approved statistics and factual evidence does show negative correlation with the amount released.

The car industry could scrap diesel tomorrow, without losing too much. Owners of cars would see more depreciation. The road transport industry, and all the shoppers it supplies would be stuffed

"However the mpg of my diesel Volvo 940 is about 50% better than my previous petrol 940 or my current petrol V90, suggesting it's not just the slightly higher energy content of the fuel"

Thanks for that Martin, I never realised diesel had 50% better MPG than petrol, though I have never learnt to drive.

Rob Burton and Martin A

Martin, how do your actual mpg figures compare with claimed mpg?

It seems that diesel claimed mpg is a reasonable reflection of actual. Petrol actual mpg is never anywhere near claimed.

Have manufacturers been rigging their claimed petrol mpg, for far more years than rigging diesel emissions?

The only petrol car I ever drove which exceeded its claimed mpg, involved hundreds of miles a week on motorways during rush hour. It could dawdle along from 20mph upto 70+ in 5th gear. I drove at less than 50mph, in 5th for much of my 40+k per annum in a 'sporty' 2l 5 dr hatch back, and got over 45mpg on average. If I did the same now in a decent diesel, I think 65+mpg would be achievable, which tallies roughly with Martin A's figures.