1.   The climate-relevant emissions covered in the plan include, apart from carbon dioxide, methane, nitrous oxide, nitrogen oxides, volatile hydrocarbons and carbon monoxide.

2.   A huge underground salt formation, where volatile hydrocarbons are stored, is the crux of the problem.

3.   But if you are dealing with volatile hydrocarbons, it has to be cleaned.

4.   They are a mixture of volatile hydrocarbons that make a fine fuel, but are considered air pollution if they escape.