Question

The atmospheric level of CO_2 is currently about 0.04% by volume. What is the concentration of CO_2 in ppm (part per million)?

Answer 1

Parts per million is self defined as amount of any measure per million of total = (no of particles or volume)/(total no. of particles or volume)*10⁶

here it is mentioned 0.04% volume means 0.04 parts of volume is present in 100 parts of volume

but we want parts per million(ppm)

let us take total volume as 100L

in 100L total volume 0.04L carbon dioxide is present
in 1litres carbon dioxide present will be 0.04/100 = 0.0004
in 10⁶(1 million) carbon dioxide present will be 0.0004*10⁶ = 400ppm