The density of air such as hydrogen, helium, ammonia and methane is significantly lower than that of air (1.29 kg/m3). In fact, in theory, as long as the above-mentioned gases are filled into the balloon, the balloon can float easily, but some gases are not suitable for filling due to their own characteristics. Among them, ammonia gas has a strong pungent odor and is easily adsorbed on the skin, mucous membranes and conjunctiva, resulting in irritation and inflammation. As the source of the smell of toilet sewers, ammonia gas is filled into the balloon, which is really not a pleasing behavior. Methane, the main component of domestic natural gas, is as flammable and explosive as hydrogen, but much heavier. Therefore, the filling gas of “hydrogen balloons” that can float on the market is often hydrogen and helium. Hydrogen and helium are the two most abundant elements in the universe, but are present in very small quantities in Earth’s atmosphere. According to statistics, due to atmospheric escape, on our earth, about 95,000 tons of hydrogen and about 1,600 tons of helium escape into the universe every year. But luckily, hydrogen isn’t actually that hard to come by because the Earth is rich in water and various hydrogen-containing compounds. However, as an inert gas, helium is difficult to form compounds with other elements, so the way to obtain helium is limited.
The entire lithosphere is estimated to produce 3,000 tons of helium every year. These helium are often captured and enriched by natural gas, and humans can separate and purify helium by mining natural gas.
