What is the relationship between the gas detection concentration units of mg/m3 and ppm?

The former is a unit of specific gravity, while the latter is a unit of volume fraction; it can be converted using the molar mass of the gas

There are two ways to express the concentration of pollutants in the ambient atmosphere (air): Mass concentration: the mass of pollutants per cubic meter of air, expressed in mg/m3. Volume concentration: the volume of pollutants in one million cubic meters of air, expressed in ppm. The gas concentrations measured by most gas detection instruments are given in terms of volume concentration (ppm). According to China’s regulations, particularly those set by the environmental protection authorities, gas concentrations must be expressed in terms of mass concentration units (such as mg/m3). Our **standard specifications also use mass concentration units (such as mg/m3) for this purpose. Using the mass concentration unit (mg/m3) as a way to express air pollutant concentrations makes it easy to calculate the actual amount of pollutants. However, the mass concentration is related to the temperature and pressure of the gas being measured, and its value changes as these environmental conditions change ； During actual measurement, it is necessary to determine both the temperature of the gas and the atmospheric pressure. When ppm is used to describe pollutant concentration, this problem does not arise because a volume ratio is employed. Conversion between concentration units ppm and mg/m3: It is calculated using the following formula: mg/m3 = M/22.4 · ppm · * (Ba/101325). In this formula, M represents the molecular weight of the gas, ppm represents the measured volume concentration, T represents the temperature, and Ba represents the pressure. For example, in the measurement of H2S removal, if the operating pressure is 8 kgf/cm2 and the temperature is 30 degrees, and the H2S concentration at the outlet is measured to be 15 PPM, then the corresponding value in mg/m3 is approximately 16. In actual production, based on experience, when H2S is below 200 PPM, it can be approximated as being below 200 mg/m3. The lower the PPM value, the greater the accuracy of the approximation to mg/m3. This post was last edited by cangying on 2007-12-19 16:35]

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