In clean air, I calculated the value of R0 by using MiCS quick evaluation board.

Formula applied :(ADC/(RESOLUTION - ADC)) * 51820---for NO2

and (ADC/(ADC-RESOLUTION))*100820 -- for CO

and in polluted air I applied same formula and gave it a name Rs

Then took ratio of Rs/R0 which is less than one.

So I had a slope and its constant meand y = m*x + c

But i do not know how to derive equation to find out the value of ppm from Rs/0