Why unleaded fuel will not stop air pollution

What you need to know:

It is good to reduce vehicle exhaust pollution. Catalysers and unleaded fuel can help achieve that. But cars are not the primary problem. And even among cars, unleaded fuel is not the primary solution

With very few exceptions, you can put leaded fuel in unleaded engines and unleaded fuel in leaded engines. And whether motor manufacturers continue to make both types of engine or not, and whether fuel companies offer either one fuel type or the other or both, you can still just carry on.

The fact is that both leaded and unleaded fuel have exactly the same “performance” characteristics. They behave in exactly the same way when you compress and ignite them. They have the same octane rating. They produce the same amount of energy in exactly the same way. For all intents and purposes, they are the same stuff. They even release roughly equal quantities of potentially harmful gases when they are burned.

The only difference is that one type has a bit of lead in it, and the other does not. It has got something else instead. Not less toxic. Just not lead.


The key point is that “unleaded” fuel is not about lead. It is about platinum. Platinum is what exhaust catalysers (catalytic converters) are lined with. It helps cause chemical reactions in car exhaust pipes that turn some active (live) gases into inert (dead) gases before they reach the back bumper. Live and harmful turned into dead and harmless. 

This platinum is quite expensive, but it will survive the hot and toxic storm in an exhaust system for ages and ages... so long as it does not get a whiff of lead. So, lead is taken out of petrol not so much to keep it out of your bone marrow, but to keep it out of your catalytic converter.

It is the other toxins which catalysers clobber that are important. But you have to get rid of the lead to allow them to do that job. If you expose them to gase substances zoom out into the street and up the nearest nose they can find.

So, the obvious conclusion is that we should all have cars with catalysers and run them exclusively on unleaded fuel. And in Sweden and Britain, they do.

And Uganda is also heading in that direction; not because it will solve our air pollution problems, but because the whole world of car makers and petroleum refiners is going unleaded. We will follow, even if only by default.

The pure rules are that if your car has a catalyser, you should only use unleaded fuel. If you have a car without a catalyser you can use either type of petrol. But failing to follow these simple rules does not cause an instant disaster. 

If you put leaded fuel in a catalyser it will stop “cleaning” your exhaust fumes before the end of its first week. The lamda sensor which “reads” the exhaust gases and tells the engine computer management system whether to enrich or lean the fuel mixture will go into “out of bounds” mode, and simply fix the air:fuel mixture at a sensible average. After a year or so, the catalyser will start to clog up and the vehicle will start to lose performance. You will then remove the catalyser and throw it away, putting a length of ordinary exhaust pipe in its place. Car back to normal.


If someone with a “normal” car fills up with unleaded fuel, it will make absolutely no difference to anything. The only exception is if the car was made in Japan before 1978 or elsewhere before 1986, and it still has its original engine valves, it will need to use an additive to lubricate the valve seats.

Lead in leaded fuel does this lubricating job. Ever since the prospect of unleaded fuel, engine valves have been made harder so they don’t need the lubrication. Not even the ones in leaded engines.

But whether you keep the rules or break them, it is important to realise that while unleaded car/fuel systems are potentially purer than leaded car/fuel systems, this difference is not guaranteed. If you put the purest unleaded fuel in a car with a perfect catalyser, it will still emit toxic exhaust fumes if the vehicle is old and worn or badly maintained or badly driven or sits in traffic jams. Such a vehicle could produce more toxic emissions than a well maintained car smoothly driven on leaded fuel without a catalyser.

In parallel with the fact that catalysers will not guarantee clean exhaust fumes, it is vital that we appreciate that clean exhaust fumes will not solve air pollution. 

We have got five times more air than England. They have got 40 times as many vehicles. So what comes out of their exhaust pipes is not as serious for them. It is 200 times as big a problem.


Even where vehicle densities are massively higher than ours, the first measures were to make vehicles smaller, more fuel efficient, service them properly, prosecute anyone whose exhaust actually smoked, force every car over three years old through a stringent annual check, progressively renew the national fleet and reduce its average age...and then, only then, after effectively addressing all those other and higher priorities to a standard of exceptional efficiency, did they start to change what was in the fuel they burned.

The point here is that in a country at an overall 1,000 times greater jeopardy of foul air than us, building a sky “scraper” of environmental measures, “unleaded” fuel is the coat of paint on the ceiling of the top floor.


I do not for one moment question the benefit of Ugandan cars being fitted with catalysers, and petrol being unleaded. What deserves attention is that these will not solve, or even significantly diminish our air pollution unless they are combined with other measures. If we somehow finish up with only catalyser cars running on only unleaded fuel, we might still choke to death, if the bigger pollution factors have not been attended to first.

This article was first published in Daily Nation