Actually, it turns out there are 20. Nicotine, formaldehyde, and 18 others.
Smoke contains 4,000 chemicals, but 3,950 of them are measurable only in nanograms and picograms.
Know how big a picogram is?
A single grain of salt weighs 100 MILLION picograms.
A lot of those smoke "chemicals" are present as only a few SINGLE picograms or less.
Our diet subjected to the same level of analysis yields TEN thousand chemicals!
Secondhand smoke IS worse than firsthand smoke, but ONLY if you snort it through a straw right from the burning end of a cigarette.
A non-smoker in a decently ventilated area with smokers will usually inhale far less than 1/100th or even 1/1000th of a cigarette per hour.
The Class A carcinogen alcohol as evaporated vapor from drinks is over 500 times as concentrated in an average bar as Class A smoke carcinogens.
A standard paperclip (NOT the big ones) weighs about 1 gram.
Straighten that paperclip into a line, for better image.
A milligram would be if you take that straightened paperclip and divided it into 1000 pieces. Each of those pieces is a single milligram.
For a nanogram, take that straightened paperclip and divide it into 1,000,000,000 (one BILLION) pieces.
For a picogram, divide the paperclip into 1,000,000,000,000 (one TRILLION) pieces.