PPM (parts per million)
Represents one part per million, that is, the number of parts of a substance contained in every million parts of a substance. Often used to express the concentration of solute in a solution or the content of a certain component in a gas. For example, 5 ppm means 5 parts per million of the substance.
%VOL (volume percent)
Refers to volume percentage, which is the percentage of the volume of a substance in the total volume. It is often used in gas mixtures. For example, the oxygen content in air is about 20.9% VOL, which means that the volume of oxygen accounts for 20.9% of the total volume of air.
LEL%（Lower Explosive Limit percent）
Refers to the percentage of the lower explosion limit. The lower explosion limit refers to the maximum concentration of flammable gas, steam or dust that can explode when exposed to a fire source when mixed with air. LEL% is a comparison of the actual measured flammable gas concentration to the lower explosive limit concentration of that gas, expressed as a percentage. For example, when the concentration of methane reaches half of its lower explosive limit (5% VOL), it can be expressed as 50% LEL.
MG/M³（milligrams per cubic meter）
Indicates the number of milligrams of a substance contained per cubic meter of volume, and is often used to express the concentration of pollutants in the air. For example, if the concentration of a pollutant in the air is 50 mg/m³, it means that every cubic meter of air contains 50 mg of the pollutant.
PPB (parts per billion)
Represents one part per billion, that is, the number of parts of a substance contained in every billion parts of a substance. Better than PPM to represent extremely low concentrations. For example, 10 ppb means 10 parts per billion of the substance.
interrelationship
· Conversion of PPM to % VOL: For an ideal gas, under standard conditions (0°C, 101.325 kPa), 1% VOL is equal to 10000 ppm. However, in actual situations, the conversion relationship may change due to different gas properties and environmental conditions.
· Conversion of PPM and MG/M³: The conversion of these two requires knowing the molecular weight of the substance and other information. For specific substances, conversions can be performed using formulas. For example, for a certain gas, at a certain temperature and pressure, if its molecular weight is M and its concentration is C ppm, its concentration in mg/m³ is:
Among them, T is the temperature (℃), and P is the pressure (kPa).
·Conversion of PPB and PPM: 1 ppm is equal to 1000 ppb.