As gases are divided into elemental gases, multivariate gases, mixed gases and organic compound gases, the substances (or elements) that make up the gas can be called the gas components. Therefore, the meaning of gas purity can be understood as: in addition to the gas composition, the number of other substances contained. For example, the purity of nitrogen refers to the amount of O2, H2, Ar, CO2, H2O, metal, dust and other impurities in addition to N components. The purity of ammonia gas refers to the number of impurities including O2, N2, CO2, H2O and dust particles in addition to NH3. If the mixture of nitrogen and helium, in addition to N2 and He components, containing O2, CO2, H2O particles and other impurities. Gas purity and its representation

Gas purity can be referred to in various ways, such as ordinary pure gas, high pure gas, electron pure, ultra pure, etc. With the development of VLSI and ULSI, there are VLSI and ULSI grade pure ultra clean gas. These terms are not very precise, just a rough description of the purity of the gas, without really showing the size of the gas purity. There are two main ways to accurately represent the purity of a gas. That is:

1. Express it as a percentage, such as 99%, 99.5%,99.9%,99.99%,99.999%,99.9999%,99.99999%, etc.

2. Use "N" for example, 3N, 5N, 4. 8 n, 5. 5N, 6N, 7N, etc., the number of N corresponds to the number of "9" in (1), and the number after the decimal point indicates the number less than "9". Such as 4 N (99.99%), 6 N (99.9999%), 7 N (99.99999%), 4.8 N (99.998%), 5.5 N (99.9995%), etc.

According to the different purity of gas, gas purity is usually divided into four levels, that is, ordinary gas, pure gas, high purity gas and ultra high purity gas.