4. The number of arguments they make The fine particles are mostly made from gases. There are four major origins for that gases which are responsible for these particles: rock (vaporized during combustion or casting), carbon from combustion, organic carbon, sulfates and nitrates. Take sulphur dioxide. It is created during engine combustion, but when it climbs into the atmosphere and mixes with rain it will become sulphuric acid. We all probably know very well what that will do- since it is highly corrosive and dangerous in concentration.