Comprising about 78% of the earth's atmosphere, nitrogen (N₂) has an atomic number of seven and an atomic weight of 14. It has a much lower solubility in water than in air—there is approximately 200 times more nitrogen in the atmosphere than in the ocean. The main source of gaseous nitrogen is volcanic eruptions; the major nitrogen sinks are synthesis of nitrate in electrical storms and biological nitrogen fixation. All organisms need nitrogen. It forms part of the chlorophyll molecule in plants, it forms the nitrogen base in DNA and RNA, and it is an essential part of all amino acids, the building blocks of proteins. Nitrogen is needed in large amounts for respiration, growth, and reproduction. Nitrogen oxides (NO_x), produced mainly by motor vehicles and internal combustion engines, are one of the main contributors to acid rain. They react with water molecules in the atmosphere to form nitric acid.

See Also

Nitrates and Nitrites; Nitrogen Cycle