Oxygen- Is used in the metal industry for welding and cutting metal. Animals need oxygen to breath.
Nitrogen- is used to make fertiliser and explosive. It can be bad because in large amounts can be very bad to human and environmental health.if there are nitrogen clumps it to can cause the the transpsort of blood to decrease
Carbon dioxide- is used in fire extinguishers. It can be used to produced carbonated soft drinks. Also trees need the CO2 that we exhale to live and in return they give us oxygen. It can be bad as in large quantities you can suffocate