Industry specification: The sensor output value unit of most sensor manufacturers is PPM. The TWA and STEL formulated by European and American countries are usually also PPM units. China has also begun to issue its own specifications, but the unit is mg/m3. In some cases, it is n

Industry specification: The sensor output value unit of most sensor manufacturers is PPM. The TWA and STEL formulated by European and American countries are usually also PPM units. China has also begun to issue its own specifications, but the unit is mg/m3. In some cases, it is necessary to convert PPM to mg/m3.

• Let’s roughly understand the definition of two units: Volume concentration representation: refers to the volume of pollutants contained in the air of one million volumes, which is commonly expressed in ppm, that is, 1ppm = cm³/m³ = 10-6, such as 5ppm carbon monoxide refers to the air containing 5 parts per million carbon monoxide. Mass volume concentration representation: the mass number of pollutants contained in each cubic meter of air, the commonly used representation unit is mg/m³ or g/m³. Formula for converting
• PPM to mg/m3

• Formula 1: mg/m3= PPM value.

serious error, but some instruments directly convert this way, so you need to pay attention.

• Formula 2: mg/m3= PPM value * constant coefficient. (Some coefficients are set to 4, 5, 7, etc.)

is relatively simple.

• Formula 3: mg/m3= PPM value* M gas molecular weight/22.4 * [273/(273+T gas temperature)] * (Ba pressure/101325).

requires the temperature and pressure of the environment, and it is difficult to use in practical applications.

• Formula 4: mg/m3= PPM value * M gas molecular weight/22.4.

is relatively scientific. VOC is a general term for a variety of gases, which has multiple molecular weights. Different companies have different types of gas emissions, so their molecular weights should also be different. It is somewhat inappropriate to use the same molecular weight method. However, many instruments cannot have built-in molecular weight, so the molecular weight fixed is more than 80, which becomes the use of formula 2 and 4 as the constant coefficient.

Below are the conversion values ​​between several common gas representation units ppm and mg/m³. They can be used as a reference when you don’t know how to choose the appropriate range:

Partial gas conversion parameters

In addition, in addition to commonly represented by ppm and mg/m³, gas concentration occasionally uses ppb and ppt. At this time, we just need to remember the conversion formulas of ppm and ppb and ppt to quickly calculate the results.