I was curious to see why Nitrogen is put into the rear shock. Does plain ole air just get contaminated? Would it be harmful to put air in the rear shock? My mountain bike stuff just uses air from my shock pump. Just curious cause i want to check the pressure, but i know it will probably lose a lot of pressure and it will probably be $$ at my local shop to refill the Nitrogen. But before i check it i just wanted to know why Nitrogen is used and if air could be substituted. Thanks for any info.