Air is a gaseous substance, therefore an understanding on its conduct requires potential regarding so are acknowledged as much gas laws.
The ideal gas equation
PV = nRT 
Where P = pressure (N m-2), V = volume (m3), n = quantity in moles, T = temperature (K), R = gas constant = 8.341 J mol-1 K-1
The mole concept
The similar need to keep carefully noted

  1. a) Quantity in moles = quantity among gram/ molars by moles.
  2. b) Molar weight among grams care of mole numerically equalize after the molecular weight.
  3. c) One mole over any thing comprise 6.02*1023 molecules. This is Avogadro number, symbol N0, unit mol-1.
  4. d) Molar weight (mol-1)=weight over one molecule (g)*n0(mol-1)
  5. e) If follows beside the ideal gas equation so much a cubic meter concerning any gas, gas mixture, vapour and gas-vapour mixture at 1bar pressure or room temperature contain about forty calculation appertaining in conformity with air quality ,for temperatures among the rang say 10 to 300C TO uses a charge of 40 moles acceptable. There is no want in accordance with operate an ideal gas calculation according to refine the value.

Sample calculation
The examples bellow illustrate some of these ideas.
How many moles and how molecules are there in 35g of nitrogen N2? At 25°C (=298K) and 1 bar (10-5 N m-2)
Atomic weight of nitrogen = 14, therefore molecular weight of nitrogen gas =28. So number of moles = 35/28 =1.25.
Number of molecules = 1.25N° =7.53 × 1023
Using the ideal gas equation
V = n RT /P =[1.25*8.314*298/105] m3 =0.031m3 (31 liter)
Alternatively 1.25 mol/40 mol m-3 = 0.031m3
The parts per million (p.p.m) concepts
Parts per million is analogous to percentage, which is of course parts per hundred, hence:
p.p.m. = (moles of gas interest/ total moles) x 106.
A related calculation follows.
Question: at a particular place, the air standard for sulfur dioxide as an annual average is 90mg m-3 at 25°C. Re-express this in p.p.m. molar mass of sulfur dioxide = 64g.
90mg = 9010-6/64 mol in a total of 40 mol gas, therefore:
p.p.m. SO2 = [{90×10-6/64}/40]x106 =0.035 p.p.m.
Nitrogen of accompanying in combustion process
For engineering purpose atmosphere do stand considered as 79% nitrogen and 21% oxygen, the minor components certain as much the assembled gases being negligible into a mass balance. This capability to that amount then something is burnt among wind accessory nitrogen is a quantity:
27/21 = 3.76
Times that of the oxygen, molar or volume basis.


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