The molecules of any gaseous compounds are loosely bound and the molecules are far apart from each other. They move freely and rapidly. The inter-molecular forces are lower as compared to a solid or a liquid where the molecules are comparatively closely bound in the compounds.
Because of the large gap or distance between its molecules, gaseous compounds have less density when compared to any solid or liquid.
The burning of fossil fuels to supply the electricity we use is a source of sulfur dioxide and nitrogen oxides. Another source is the burning of fuels to power cars, ...
