What Is the Relationship Between the Gas Detection Concentration Units mg/m³ and ppm?
There are two ways to represent the concentration of pollutants in the ambient atmosphere (air):
1. Mass concentration expression method: the mass of pollutants contained in each cubic meter of air, i.e. mg/m3
2. Volume concentration representation: The volume of pollutants contained in one million volumes of air, i.e. ppm. Most gas detection instruments measure gas concentration in terms of volume concentration (ppm). According to Chinese regulations, especially the environmental protection department, gas concentration is required to be expressed in units of mass concentration (such as mg/m3), and our national standards and specifications also use units of mass concentration (such as mg/m3).
What is the relationship between the concentration units of these two gases in mg/m3 and ppm? How to convert between them? The use of mass concentration units (mg/m3) as a representation of air pollutant concentration can facilitate the calculation of the true amount of pollutants. But the quality concentration is related to the temperature, pressure and environmental conditions of the detected gas, and its value will vary with changes in temperature, pressure and other environmental conditions; During actual measurement, it is necessary to simultaneously measure the temperature and atmospheric pressure of the gas. When using ppm to describe pollutant concentration, this problem does not occur due to the use of volume ratio.
The conversion between concentration units ppm and mg/m3 is calculated using the following formula:
Mass concentration mg/m3=M gas molecular weight/22.4 * ppm value * [273/(273+T gas temperature)] * (Ba pressure/101325)
M is the molecular weight of the gas, ppm is the measured volume concentration value, T is the temperature, Ba is the pressure. If the humidity is high, such as at 100% relative humidity, another item is required. Gas molecular weight [Common gas molecular weights: formaldehyde HCHO is 30.0260, benzene C6H6 is 78.1118, ammonia NH3 is 17.0306]
