And smell the gaseous element, atomic number, atomic weight 1 1. 008; the easiest and perhaps most common chemical element in the universe. However, it is found only in trace amounts in the observable part of the atmosphere at a rate of only about 0. 00005% by volume of dry air. Hydrogen H2 has a molecular weight of 2. 0160 and specific gravity of air referred to 0. 0695 low escape velocity of hydrogen, in combination with the lack of active creation on Earth, has its concentration to negligible amounts. Its concentration increases above a height of a few hundred kilometers from diffusion separation. At one time hydrogen is widely used for pumping of weather balloon, but due to its dangerous flammability, it was replaced by helium.