Show that an SO2 atmospheric concentration of 0.2 ppb(v) is equivalent to 0.4 ppb(w) stands for weight and ppb(w) refers to the number of tonnes (or grams) of SO2 in 10^9 tonnes (or grams) of air.
The (v) of ppb (v) stands for volume.
The ppb stands for parts per billion.
Every unit volume of atmospheric air contains (on average) 0.2 x 10^-9 units volume of Sulfur Dioxide.
You should be able to find the numbers cited below in your textbooks, however, just in case, here are some web links you may want to ...
Fractions, ratios parts per billion are investigated. The solution is detailed and well presented. The response received a rating of "5/5" from the student who originally posted the question.