Edited sentence: Additionally, the standard general aviation fuel for piston aircraft still includes lead, which is particularly bad for the environment.Aircraft have a particularly marked impact on the environment, compared with other commonly used vehicles.However, the most significant impact of such aircraft upon the environment is their contribution of greenhouse gases.Their contrails contribute to global dimming, and their noise is often significant.They are responsible for emitting a great deal of carbon monoxide and nitrogen dioxide, and they distribute the gases more evenly on a global level and far higher in the atmosphere than any other commonly used vehicle type