When we exhale our cloud proudly after vaping, satisfied with ourselves and the impressiveness of the white behemoth spreading across the space ahead of us, we know we're having a good day. Ever since the conception of the E-Cigarette we've called this vapour. In fact we named the term 'vaping' after it. It makes sense, the E-Liquid is being heated until it becomes vapour which is then inhaled and finally exhaled. But the big question is: is it vapour? And if not, then what do we call it? I've obviously heard it called vapour, but also aerosol and particulate matter.
In a regular definition of the term, vapour is the gas phase of a liquid. In a glass of water microscopic bits of that water are constantly evaporating into the air and that is “water vapour”. If the temperature of the liquid goes up then more of the water will begin to evaporate into the air as it gets hotter and hotter. This applies to anything that is liquid. So in turn this does mean that e-cig's “vapour” does contain some actual vapour, but it is still mostly in its liquid phase? Meaning it contains very tiny droplets of the liquid suspended in the air, not actually in a gas phase, being that they are “suspended” and are physically mixed with the air. This suspension in the air is not a vapour but an aerosol.
Definitions of what an aerosol is usually include solid particles which are suspended in the air and not just liquid droplets. In fact, smoke could be considered an aerosol since it has both solid and liquid particles in it which are suspended in the air. So, in its truest definition, the material that an e-cig gives off should actually be called liquid aerosol, as the e-liquid does not completely vapourize, rather it leaves very tiny liquid particles that mix with the air around you. In regular circumstances, the area that you are vaping in allows for the microscopic particles to evaporate quickly, this is why the “vapour” disappears very quickly. You should also know that matter being labeled an “aerosol” also means it is stable enough to be one. With normal air conditions electronic cigarette “vapour” disappears rather quickly so it is not really stable enough to be called an “aerosol”. However, scientists often call the material “aerosol” despite it not being as stable as a usual aerosol, but it's still a practical label for it.
But what about those who refer to it as 'particulate matter', in fact, what does that even mean? By the common scientific definition, it's anything that is suspended in an aerosol. Confusing right? With the definition of aerosol I've just given you this could lead someone to call the droplets themselves particles, however particles are actually objects, albeit very small ones. So you can't describe these droplets as particles at all. The problem with some reporters referring to E-cig vapour as particles is obvious as particles are solid objects that would cause damage were they to be inhaled, like the particles of tar that you inhale from tobacco cigarettes that build up in the lungs.
So what, then, do we inhale and exhale from ecigs? I suppose, scientifically, it would be a liquid aerosol. Certainly not a particulate matter, but not entirely vapour either. Though don't worry, it's still not harmful.
I think though, I'll still go on to refer to it as vapour and vaping. It just sounds better than liquid aerosoling.