converting from mg/nm3 to ppm

hi there guys- i have a list of pollutants that are expressed as mg/nm3- i need to convert to ppm so that i can compare the readings to the standards. if anyone can help, thanks!!
e.g of pollutants: particulate matter; so2, nox, co coal, co biomass etc.

[Mrs X]

Originally Posted by Unregistered

hi there guys- i have a list of pollutants that are expressed as mg/nm3- i need to convert to ppm so that i can compare the readings to the standards. if anyone can help, thanks!!
e.g of pollutants: particulate matter; so2, nox, co coal, co biomass etc.

Hi, for gas systems, ppm is µL/L. If your "n" is lower case, then it might mean nano-cubic meter (????) if the "n" is upper case, then it would mean normal cubic meter, which will be at a specific temperature and pressure. - I think the second is MUCH more likely, but then again, I'm very often wrong, and it could be something completely different.

First, you need to establish what volume you are actually talking about, then convert your mg to a volume as well. To do this, work out how many moles you have.

1 mole of ideal gas at 1atm occupies 24.5L at 25°C, according to the SI chemical data book.

If this is for an assignment, is this enough information to help you on the right track? - Please post back if you need more help, or if you have more info.

yea sorry it is mg/Nm3- its not for an assignment- i deal with air quality stds- can u give me a step by step- here is 1 of the pollutants
So2- 30 mg/Nm3= ? ppm - i need to see wat it is in ppm so that i can compare to the stds[ which r in ppm]- thx a mill

Hi, been dealing with this myself lately. To convert to ppm you need to know the density of the gas you are dealing with. For example, for Nox. Nox density is 1.912 mg/mL at standard conditions. Therefore you need to bring the Nox density to the actual temp and press your dealing with. For emissions this will generally be a high temp at almost atm press. You can do this by using the combined gas law.

Here would be the example for a 25 mg/m3 of Nox at 425 k and 100 kPa.

The density Nox at those conditions would be = 1.228 mg/mL (found using the combined gas law). Now that you know the density of the Nox, you can find the ppm by the following: = 25 mg/m3 / 1.228 mg/mL = 20.3 mL/m3 which is the same as 20.3 ppmv. This does not correct for O2, so don't miss that since most standards correct to 15% O2. Hope this helps.

[Mrs X]

Originally Posted by Unregistered

yea sorry it is mg/Nm3- its not for an assignment- i deal with air quality stds- can u give me a step by step- here is 1 of the pollutants
So2- 30 mg/Nm3= ? ppm - i need to see wat it is in ppm so that i can compare to the stds[ which r in ppm]- thx a mill

Hi, the poster above has given a very useful method of working these out. NOx, usually looked for in vehicle emissions, is a bit different as it can be in the forms N2O through to NO2, so they take an average.

If you want a step by step method which will work for any gas, please can you let us know what temperature and pressure your "normal" is? It can be different for different industries, but is often 1 bar or 1atm pressure, and 20 or 25°C. Also, if your company is audited at any stage, you may need to pay a consultant to get traceable info. The auditors might not accept something you got over the internet

Originally Posted by Unregistered

yea sorry it is mg/Nm3- its not for an assignment- i deal with air quality stds- can u give me a step by step- here is 1 of the pollutants
So2- 30 mg/Nm3= ? ppm - i need to see wat it is in ppm so that i can compare to the stds[ which r in ppm]- thx a mill

For gas:
1ppm=M/22.4 mg/Nm3 (M as the mole of the gas)

Ur question's answer 30mg/m3=30*22.4/64ppm=10.5ppm 64 is mole of SO2

Originally Posted by Unregistered

hi there guys- i have a list of pollutants that are expressed as mg/nm3- i need to convert to ppm so that i can compare the readings to the standards. if anyone can help, thanks!!
e.g of pollutants: particulate matter; so2, nox, co coal, co biomass etc.

Re: converting from mg/nm3 to ppm

Originally Posted by Unregistered

Re: converting from mg/nm3 to ppm

hi! i've learnt how to convert from mg/Nm3 to ppmv for gases from the above conversation and vice versa by back calcs, but now i'd like to know how can or how does one accounts for say maybe 10% O2 in the calculated mg/Nm3 value as per the standard? (i.e the standard say mg/Nm3 at standard conditions of 273.15 K, 101.325 kPa and 10% O2)


thnx in advance.

[JohnS]

Originally Posted by Unregistered

hi! i've learnt how to convert from mg/Nm3 to ppmv for gases from the above conversation and vice versa by back calcs, but now i'd like to know how can or how does one accounts for say maybe 10% O2 in the calculated mg/Nm3 value as per the standard? (i.e the standard say mg/Nm3 at standard conditions of 273.15 K, 101.325 kPa and 10% O2)


thnx in advance.

The O2 spec is one way to specify how much excess air the combustion process is running. Usually the level of excess air will change the level of emissions and I don't know a good way to compensate for it.

A gasoline engine with emission controls is usually run at stoichiometry, where the oxygen in the air is just sufficient to combust all the fuel. There is no O2 in the exhaust. Ideally, it is all "burnt" to CO2 and H2O (with some pollution in the form of CO, NOx, and unburnt hydrocarbons, but very small percentages of total mass of intake air and fuel).

Other types of engines (diesel, turbines) run large volumes of excess air. O2 makes up 21% of intake air, but how much goes to CO2 and to H2O depends on the fuel composition. However, if there is excess air, some is not changed and passes to the exhaust.

Usually, this profoundly changes the level of pollution the engine is throwing. I think you have to load the engine up to match the spec. I'm not aware of a way to meaningfully adjust it to standard.

Stack Monitoring Emission report we can change the unit for mg/Nm3 to ppm.

Originally Posted by Unregistered

hi there guys- i have a list of pollutants that are expressed as mg/nm3- i need to convert to ppm so that i can compare the readings to the standards. if anyone can help, thanks!!
e.g of pollutants: particulate matter; so2, nox, co coal, co biomass etc.