Mass
Mass refers to the weight of a gas, usually expressed in milligrams (mg), grams (g), kilograms (kg), or tons (t). Volume refers to the capacity of the container in which the gas resides. It is usually expressed in cubic millimeters (mm³), cubic centimeters (cm³), or cubic meters (m³). Specific volume is the volume occupied by a unit weight of a substance, represented by the symbol V. The unit for specific volume of gases is m³/kg, and for liquids it is l/kg.
Pressure, Atmospheric Pressure, Absolute Pressure, Relative Pressure
Pressure is the force exerted by gas molecules on the walls of a container during their motion. The pressure exerted per unit area of the container is called pressure intensity. The unit of pressure intensity is conventionally millimeters of mercury (mmHg) per square centimeter (cm²), but internationally accepted (legal measurement) units include Pascals (Pa), kilopascals (kPa), and megapascals (MPa). After conversion, 1 mmHg = 133.3 Pa = 0.1333 kPa, 1 MPa = 1000 kPa = 1000000 Pa, 1 ATA = 0.1 MPa.
Temperature, also known as absolute temperature, relative temperature, critical temperature, and critical pressure.
Temperature is the statistical average of the thermal motion of molecules in a substance. Gas temperature is generated by the thermal motion of gas molecules. The unit of gas temperature is commonly expressed in Celsius (°C), with 0°C being the freezing point of water. In physics, absolute temperature is commonly used, represented by "K". Absolute temperature is defined as -273°C as zero. The relationship between Celsius and absolute temperature is T = t + 273. British scientists also frequently use "Fahrenheit temperature," symbolized as °F.
Purity
Purity is an important technical parameter for gases. Taking nitrogen as an example, according to national standards, nitrogen is classified into three grades based on purity: industrial nitrogen, pure nitrogen, and high-purity nitrogen. Their purities are 99.5% (O2 ≤ 0.5%), 99.99% (O2 ≤ 0.01%), and 99.999% (O2 ≤ 0.001%), respectively.