Why do cars smell like rotten eggs after a while? Is this down to catalytic converters?

Why do cars smell like rotten eggs after a while? Is this down to catalytic converters?

This is not exactly a myth but is something that's becoming less of an issue nowadays. The reason that that happens is that there is sulphur in fuel and when sulphur burns in oxygen it forms sulphur dioxide. This only really happens in a petrol engine, which can operate under fuel-rich or fuel-lean conditions. In fuel-lean conditions there's quite a lot of oxygen so the sulphur in the fuel gets oxidised to sulphates. This is a real pain because this clogs up the catalyst and builds up on the surface of the monolith. But when you start a car, this is the point when you have fuel-rich conditions. This is going to convert the sulphate that has built up on the catalyst into H2S, which is hydrogen sulphide. That's the kind of eggy smell that you get out. But this is also why we're getting a lot more low-sulphur fuels nowadays and to be honest it's a lot less of a problem than it used to be.

Why can you smell some gases, but not others ?

Why can you smell some gases, but not others ?

Actually, methane doesn't smell either, but you probably thought it did because it is often found with hydrogen sulphide which is very stinky and smells just like rotten eggs. Gases get into our noses to excite our olfactory (or smelling nerves) which are connected to our brains to allow us to smell. How a gas smells depends on it's size and shape, and how it can fit into our smell receptors in the nose. It also depends of course on how easily a gas evaporates. Gases which evaporate more easily smell stronger because more vapour manages to get into the nose. Gases which smell tend to be the ones which are heavier, and more than 15 times the weight of hydrogen which is the smallest atom, so methane and carbon monoxide (CO) don't smell but hydrogen sulphide (H2S), and chlorine (Cl2) do. Why does it smell when we break wind? This is because the your gut contains lots of bacteria and enzymes to digest your food and in this process gases like hydrogen sulphide (H2S) are produced. Interesting fact - we break wind on average 14 times a day. However a word of warning, if the concentration of hydrogen sulphide increases too much, your olfactory, or smelling, nerves are paralysed and you lose the ability to smell it. Other gases which don't smell are Oxygen, Nitrogen, and steam. Gases which do smell include chlorine, bromine, iodine and sulphur dioxide.