The impact of flying extemds further than just CO2 emissions. On top of the carbon dioxide, aircraft also emit many other hazardous gases. Some examples of gases released are various nitrous oxides, sulfur dioxide and water vapour, alongside this is also the issue of particular matter or soot. Fortunately there are effective solutions that can mitigate many of these effects, one example is the cleaning up of fuel used in planes to reduce their aromatic and sulphur content, as they are the main driver for what is emitted. This can be done thanks to a refinining process called hydrotreatment, in which hydrogen is added to refinery products at a certain temperature and pressure to change their composition.