Dear Anand Dev Gupta,

use following calculator: http://www.lenntech.com/calculators/ppm/converter-parts-per-million.htm

Br

Marek Maasikmets

Hi. The formula is the following:

(µ𝑔)⁄𝑚^3 =concentration (𝒑𝒑𝒃)×(molecular weight of the gas(𝑔⁄𝑚𝑜𝑙))/(standard molar volume of ideal gas (𝐿))

𝑚𝑔⁄𝑚^3 =concentration (𝒑𝒑𝒎)×(molecular weight of the gas(𝑔⁄𝑚𝑜𝑙))/(standard molar volume of ideal gas (𝐿))

The standard molar volume of ideal gas at 1 atm. pressure:

You can use the equation below

ppm = mg/L =mg/kg = 103 mg/m3

In Testo 350 XL manuel, unit conversion equations are included.

https://static-int.testo.com/media/42/e7/f95897396990/testo-300-Instruction-manual.pdf

You can see the equations in Page 37

Please consider this formula:

mg/Nm3 = PPM * MW/22.4

for example for 350 mg/Nm3 convert to PPM its done as below: MW of NO2= 46

350 mg/Nm3 / (46/22.4) = 170 ppm