When can I convert mg/m3 to ppm

discussion with shri jkp sir for quality improvements in analysis

If ppm is expressed as THE VOLUME of particles to a unit volume of water, thenppm BY VOLUME is equal to µl/l. However, if ppm is expressed as THE MASS of particles in a unit volume of water, then ppm BY MASS is equal to mg/l. To convert from ppm by volume to ppm by mass, multiply by the density of the particles.Apr 5, 2011

PPM = parts per million. PPM is a term used in chemistry to denote a very, very lowconcentration of a solution. One gram in 1000 ml is 1000 ppm and one thousandth of a gram (0.001g) in 1000 ml is one ppm. One thousanth of a gram is one milligram and 1000 ml is one liter, so that 1 ppm = 1 mg per liter = mg/Liter.  

How is ppm related to concentration

ppm vs concentration in mg/l or µl/l? [Sequoia, April 5, 2011] How is ppm related to concentration? ppm means parts-per-million. But what parts? The amount of particles in a suspension can be expressed as the total volume OR total mass of particles in a unit volume of water AND THESE TWO NUMBERS WILL ONLY BE THE SAME IF THE DENSITY OF THE PARTICLES IS 1 g/cm3. If ppm is expressed as THE VOLUME of particles to a unit volume of water, then ppm BY VOLUME is equal to µl/l. However, if ppm is expressed as THE MASS of particles in a unit volume of water, then ppm BY MASS is equal to mg/l. To convert from ppm by volume to ppm by mass, multiply by the density of the particles. For mineral grains (clay, silt and sand sizes), this will typically be 2.65 g/cm3. For example, a sample with a volume concentration of 25 µl/l will have a mass concentration of 25*2.65 = 66 mg/l. To convert from ppm by mass to ppm by volume, divide by the density of the particles. For example, a sample with a mass concentration of 100 mg/l will have a volume concentration of 38 µl/l. When ppm is used as a measure for the suspended particle concentration, it is therefore very important to specify if the concentrations are ppm BY VOLUME or ppm BY MASS, to facilitate comparisons with data where the concentrations are reported in µl/l or mg/l.

When can I convert mg/m3 to ppm

When can I convert mg/m³ to ppm?

Occupational exposure limits (OELs, TLVs, PELs, etc.) can be expressed in parts per million (ppm) only if the substance exists as a gas or vapour at normal room temperature and pressure. This is why exposure limits are usually expressed in mg/m³. However, some OELs may be expressed in units such as fibres/cc (e.g., for asbestos). OELs for metals, salts and other compounds that do not form vapours at room temperature and pressure are expressed in mg/m³ only. 

What is the usual way of converting mg/m³ to ppm?

The ACGIH booklet "Threshold Limit Values (TLVs™) for Chemical Substances and Physical Agents and Biological Exposure Indices (BEIs™)" uses the formulas: 

These formulas can be used when measurements are taken at 25°C and the air pressure is 760 torr (= 1 atmosphere or 760 mm Hg). 

What is gram molecular weight?

Gram molecular weight is the molecular weight (MW) expressed in grams. For example, the gram molecular weight for toluene is 92.13 g. since the molecular weight is 92.13. A gram molecular weight is also called a gram mole. 

How do I convert mg/m³ to ppm at different temperatures and pressures?

The number 24.45 in the equations above is the volume (liters) of a mole (gram molecular weight) of a gas or vapour when the pressure is at 1 atmosphere (760 torr or 760 mm Hg) and at 25°C. 
To convert mg/m³ to ppm at other temperatures and pressures, one must calculate the volume of 1 gram molecular weight of an airborne contaminant (e.g. 92.13 grams of toluene) by using the formula: 
V = (RT/ P) 
where R is the ideal gas constant; T, the temperature in  kelvins (273.16 + T°C); and P, the pressure in mm Hg. This information can be substituted in the formulas for converting between mg/m³ and ppm. 

where the value of R is 62.4 when the temperature (T) is in kelvins, K (=273.16 + T°C), the pressure is expressed in units of mm Hg and the volume is in liters. There are different values for the gas constant R if the temperature is expressed degrees Fahrenheit (°F) or if other units of pressure (e.g., atmospheres, kilopascals) are used.?

- January 10, 2014   

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