## Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

## Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

(OP)

Hi there all,

We are doing frequent measurements of contaminants like H2S, Hg, As in our gas streams, as well as for the concentration of same in air around out plant. Unfortunately, units used to specify limits, readings from meters, etc are rarely consistent, and in many cases open to interpretation. E.g. PPM, which could be either PPM (wt) or PPM (vol), or g/m3, which does not specify whether the gas is at actual or standard condition (which makes a big difference in case of sales gas).

Originally, I was told that:

ppm (wt) x 1000x Density = mg/m3, and

ppm (vol)x1000 = mg/m3

However, this does not take into consideration the density of the gas the contaminant is measured in. I tried searching on the net for conversion factors/formulas, but without success.

Any help available?

We are doing frequent measurements of contaminants like H2S, Hg, As in our gas streams, as well as for the concentration of same in air around out plant. Unfortunately, units used to specify limits, readings from meters, etc are rarely consistent, and in many cases open to interpretation. E.g. PPM, which could be either PPM (wt) or PPM (vol), or g/m3, which does not specify whether the gas is at actual or standard condition (which makes a big difference in case of sales gas).

Originally, I was told that:

ppm (wt) x 1000x Density = mg/m3, and

ppm (vol)x1000 = mg/m3

However, this does not take into consideration the density of the gas the contaminant is measured in. I tried searching on the net for conversion factors/formulas, but without success.

Any help available?

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

it has a rather extensive concentration conversion calculator. just as an aside this is the conversion base:

1ppm=1 mg/l=1 mg/kg

1ppb=1 micro g/l =1 micro g/kg

1ppm=1000ppb

1mg/l=1g/m^3

Hope this helps.

saxon

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

Since ideal gas behavior of all constituents is also typically assumed a correction to standard temperature and pressure isn't necessary.

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

http://www.scottecatalog.com/scotttec.nsf/74923c9ec562a6fb85256825006eb87d/79ab7a1827b36ff6852569a7005270c3?OpenDocument. On questions like this the industrial gas manufacturers sites may be helpful. Matheson (at wwww.trigas.com and www.BOC.com (British Oxygen).

HAZOP at www.curryhydrocarbons.ca

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

I've been having difficulty sending an E-mail to you. You will be able to get the downloads at www.process-notes.co.uk. Go to the "Our Products" page, then the "FREE ... downloads" page, and you'll find links there. Leave it a day before you try - I'll upload the modified pages tonight, ISP and hosts willing! (GMT here, presently 8am.)

Stuart

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

=>From ppm

_{v}to g/L one needs to know the density of the solute.=>From ppm

_{w}to g/L one needs the density of the solution, which, if very dilute, can be replaced (with little error) by the density of the solvent.## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

Nm3 stands for "normal" or "standard" cubic meter from the perfect gas equation. You therefore have to correct both parameters to obtain an accurate value.

Temperature and pressure: use pv=RT equation to calculate the volume of the compound under the actual and standard conditions.

O2%: use O2 actual = 21/(21- O2 measured)

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

the correction formula is

O2 corrected figure= non corrected figure*(21-O2reference)/(21-actualO2) ; O2 reference can be 11%, sometimes 7% or other values).

pollutants like dust SO2 HCl are often mg/Nm3, dry, O2 corrected

pollutants like NOx can ne either

It is important to understand the dramatic effect of O2 correction, if you have actual O2 figures exceeding 17-18%.

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

[mg/m3] = (MW x PPM) / vol

where; MW = molecular weight, PPM = parts per million, vol = volume in liters of one mole of gas.

You can then correct the volume to actual process conditions and as such carry through the correction to your concentration conversion.

Take example:

H2S = 120 PPM, gas consituents are 70% N2, 5% H2O as vapour, 15% CO2 and 10 % O2, therefore density at NTP is approx 1.352 kg/Nm3.

Lets say P = 110 kPa and temp is 50 degrees C

Therefore density (actual) = 1.242 kg/Am3

Now calculate actual volume:

Vol of air at actual conditions = 24.43 L, density air (acutal) with 5% moisture = 1.163 kg/Am3.

Therefore actual vol = (1.163/1.242)*24.43 = 22.876 L

As such [mg/m3] H2S = 34.0818 x 120 / 22.876 = 178.78

Cheers.

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

If the gas is considered "ideal", 120 ppm v/v of H2S at

actual conditionswould still be 120 ppm v/v at NTP = 120 mL/m^{3}.To convert 120 mL H2S into mg at NTP (0 deg C, 1 atm abs.):

120 mL/m

^{3}x 1.5392 mg/mL = 184.7 mg/m^{3}at NTP.However, the same 1 m[sup]3[/sub] of gas at NTP would expand under "actual" conditions (50 deg C, 110 kPa) to:

1 x [(273+50)/273] x 101.3/110 = 1.09 m

^{3}.Thus since its mass doesn't change, the adjusted H2S concentration would be:

^{3}under actual conditions.

Please correct me if I'm wrong.

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

You have asked for too many different conversions and that has led to the confusing array of responses.

This response of mine applies only to converting ppmv of a gaseous pollutant in the ambient air to mg of the gaseous pollutant per cubic meter of ambient air at a pressure of 1 atmosphere and any temperature:

ppmv = (mg/m

^{3})(273.15 + °C) / (12.187) (MW)where:

ppmv = volume of gaseous pollutant per 10

^{6}volumes of ambient airmg/m

^{3}= milligrams of gaseous pollutant per cubic meter of ambient airMW = molecular weight of the gaseous pollutant

°C = ambient air temperature in degrees Celsius

{Also, note that the ambient air pressure has been incorporated into the above equation as being 1 atmosphere)

For a more detailed discussion of this and related conversions involved in air pollution, visit www.air-dispersion.com/formulas.html

Milt Beychok

## RE: Conversion PPM(wt), PPM(vol), g/m3 (gas phase)

^{3}/kg-mol.